essay on xerophytes

Essay on Xerophytes

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100 Words Essay on Xerophytes

Introduction to xerophytes.

Xerophytes are special types of plants that have adapted to survive in harsh dry areas with little water, like deserts.

Adaptations of Xerophytes

These plants have unique features like thick, waxy leaves and deep roots to store and conserve water.

Examples of Xerophytes

Cacti and succulents are common examples of xerophytes. They can survive long periods without water.

Importance of Xerophytes

Xerophytes are crucial for maintaining biodiversity in dry habitats and help to prevent desertification.

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250 Words Essay on Xerophytes

Introduction.

Xerophytes are specialized plant species that have adapted to survive in extremely dry environments, such as deserts. These plants have evolved unique physiological and morphological characteristics that enable them to withstand harsh conditions where water is scarce.

Xerophytes have developed several adaptive strategies to conserve water. They possess thick cuticles and a reduced leaf surface area to minimize water loss through transpiration. Some xerophytes, like cacti, have their leaves modified into spines, and photosynthesis occurs in the stem. Succulent xerophytes store water in their thick, fleshy tissues, providing reserves during prolonged droughts.

Root System

The root systems of xerophytes also exhibit adaptations. Many have extensive and deep root systems to tap into underground water sources. Some species have shallow but widespread roots to absorb surface water quickly after rare rainfalls.

Reproductive Strategies

Xerophytes have evolved reproductive strategies to ensure their survival. Many produce seeds that can remain dormant in the soil for years until conditions are favorable for germination. Some also reproduce asexually through stem cuttings, which require less energy and resources.

Ecological Significance

In conclusion, xerophytes are remarkable examples of plant adaptation and survival. Their unique characteristics not only allow them to inhabit some of the world’s most inhospitable environments, but also contribute to the biodiversity and resilience of these ecosystems.

500 Words Essay on Xerophytes

Xerophytes are remarkable organisms that have adapted to survive in harsh, arid environments, such as deserts, where water is scarce. These plants have evolved unique physiological and morphological characteristics that help them thrive in conditions that would be inhospitable to most other plant species.

Many xerophytes also have stomata, pores through which gas exchange occurs, located in deep pits or covered by hair-like structures. These adaptations further reduce transpiration by trapping a layer of humid air around the stomata. Some species even have the ability to close their stomata during the day when evaporation rates are high, opening them only at night when conditions are cooler and more humid.

Another characteristic feature of xerophytes is their ability to store water in their tissues. Succulent xerophytes, like cacti, have thick, fleshy stems and leaves that can store large amounts of water during periods of rainfall, providing a reservoir for the plant to draw upon during dry periods.

Root Systems of Xerophytes

Reproductive strategies of xerophytes.

The reproductive strategies of xerophytes are equally adaptive. Many produce seeds that can remain dormant in the soil for years until conditions are favorable for germination. Others reproduce vegetatively, through the growth of new plants from existing plant parts, a strategy that requires less water than seed production.

Ecological Role and Importance of Xerophytes

Despite their harsh environments, xerophytes play vital roles in their ecosystems. They provide food and shelter for a variety of animals and help to stabilize soils, preventing erosion. Additionally, they are important in human economies, with many species used for food, medicine, and ornamental purposes.

Xerophytes are a testament to the power of adaptation. Their specialized structures and behaviors allow them to survive and even thrive in some of the harshest environments on earth. These plants not only underscore the diversity of life but also remind us of the importance of conserving and protecting all forms of life, no matter how seemingly inhospitable their habitats.

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Water is a common denominator for all life on earth. Regardless of size or complexity, all life requires water to survive. However, water is not always readily available. An organism’s ability to obtain and keep water determines whether it will survive, particularly in a dry environment. Xerophytes are plants that have structural adaptations that help them survive in dry habitats. Small, thick leaves reduce the amount of surface area through which evaporation takes place. Other xerophytic adaptations that act to reduce water loss include waxy or hairy leaf coverings, multiple layers of epidermal cells, water storage in air spaces within the leaf, changing leaf position to reduce sunlight absorption, and dropping leaves during dry periods.

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Ecological Adaptations of Xerophytes (with PPT)

What are xerophytes.

Ø   Xerophytes (xerophytic plants) are plants growing in dry habitats (xeric conditions) where the availability of water is very less. Xeric habitat are the places where water is NOT present in adequate quantity.  Xerophytes are the characteristic plants of deserts or semi-deserts areas. Xerophytes can also grow in mesophytic conditions. The present post discusses the Morphological, Anatomical and Physiological Adaptations of Xerophytes.

Ø   Xerophytes can tolerate:

$.  Extreme dry condition

$.  Low humidity

$.  High temperature

$.  High wind-flow

Ø   Three types of xeric habitats occurs on the earth:

(1). Physically dry habitat: the water retaining capacity of the soil very low and climate is dry (Example: a desert).

(2). Physiologically dry: water is present in excess, but not in the absorbable conditions or the plants cannot absorb it (Example: high salt water, high acidic water and high cold water, water as snow).

(3). Physically and physiologically dry: water present as mist, plants cannot absorb water from the atmosphere directly. (Example: mountain slopes)

Examples of Xerophytes:

(1). Ephemeral Xerophytes: – Short lived xerophytes

Examples: Tribulus terrestris, Trianthema monogyna, Carthamus oxyacantha

(2). Succulent Xerophytes: plants with fleshy and succulent parts, two types:

(a). Succulents with fleshy stem: Opuntia, Echinocactus, Euphorbia royleana

(b). Succulents with fleshy leaves: They are also called as Malacophyllous xerophytes: Example: Aloe, Agave, Peperomia,  Haworthia , Bryophyllum, Kalanchoe

(3). Non-succulent xerophytes: Nerium, Cassuarina, Pinus, Calotropis, Ephedra, Equisetum

Adaptations strategies of xerophytes:

o    To absorb as much of water as they can get from the surroundings.

o    To retain water in their organ for very long time.

o    To reduce the water loss by transpiration to minimum.

o    To prevent high consumption of water.

Classification of Xerophytes:

Ø   Xerophytes are classified on the basis of their drought resisting power.

Ø   They are classified as:

(1).  Drought escaping plants

(2).  Drought enduring plants

(3).  Drought resistant plants

(1). Drought Escaping Plants:

Ø   They are short lived plants (ephemerals) and they complete their life cycle within few weeks.

Ø   They survive in the critical dry periods as seeds or propagules.

Ø   They have hard and resistant fruit walls and seed coats for protecting the embryo from extreme dry conditions.

Ø   These plants germinate suddenly in the favourable conditions.

Ø   They are usually short sized plants in which the flowering and fruiting occur before the next unfavourable season.

Ø   Example: Astragalus, Artemesia, Tribulus and most of the grasses.

(2). Drought Enduring Plants:

Ø   They are small sized plants that have the capacity to endure or tolerate drought conditions.

Ø   These plants usually do not show any xerophytic adaptations.

Ø   Most of the individuals in the population will die in the unfavourable season; the surviving ones contribute the next generation.

(3). Drought Resistant Plants

Ø   They are the true xerophytic plants that can resist the drought conditions.

Ø   They develop adaptations to resist the extreme temperature and drought.

Ø   On the basis of water storing capacity, xerophytes are classified into two groups:

(1). Succulent xerophytes: they can store water in their plant body.

(2). Non-succulent xerophytes : also called true xerophytes.

Xeromorphic vs Xeroplastic Characters

      Plants show TWO types of xerophytic characters (adaptations), they are:

(1). Xeromorphic characters:

Ø   Xeromorphic characters are fixed xerophytic characters.

Ø   These characters appear in the xerophytes irrespective of the environmental conditions.

Ø   Example: Sunken stomata in Cycas; Some cactoid Euphorbias.

(2). Xeroplastic characters:

Ø   Xeroplastic characters are induced by droughts conditions in the plants.

Ø   These characters only appear in plants when they are challenged by xeric conditions.

Ø   These characters are not genetically fixed and thus they are not inherited to the next generation.

Xerophytic Adaptations of Plants

Ø   Xerophytic characters shown by plants can be grouped into the following THREE categories:

(1). Morphological adaptations: external adaptations

(2). Anatomical adaptations: internal adaptations

(2). Physiological and Reproductive adaptations

Morphological Adaptations of Xerophytes:

(a). Roots of xerophytes

Ø   Root system is well developed in true xerophytes.

Ø   They are adapted to reach the area where water is available and to absorb water as much as possible”.

Ø   Roots will be profusely branched and more elaborate than their stem.

Ø   Most of the roots in xerophytes are perennial and they survive for many years.

Ø   Roots grow deep into the soil and they can reach a very high depth in the soil.

Ø   Root surface is provided with dense root hairs for water and mineral absorption.

(b). Stem of xerophytes

Ø   Stem woody and hard in some xerophytic plants.

Ø   Stem usually green and photosynthetic.

Ø   Stem is covered with thick cuticle, wax and silica (Example: Equisetum).

Ø   In many plants, the stem is covered with dense hairs (Example: Calotropis).

Ø   Stem modified into thorns in Ulex.

Ø   Succulent and bulbous xerophytes can store water in their stem. Example: Cactus and some species of Euphorbia.

Ø   Stem may be modified into phylloclades, cladophylls or cladodes.

Ø   Phylloclades : Stem modified into flattened leaf-like organs (Muehlenbeckia).

Ø   Cladode : Many axillary branches become modified into small needle like green structures which look exactly like leaves (Asparagus).

Ø   Cladophyll : branches developed in the axil of scale leaves, become metamorphosed to leaf-like structures (Ruscus).

(c). Leaves of xerophytes

Ø   Leaves usually absent in xerophytes.

Ø   If leaves are present, usually they are caducous (fall off easily).

Ø   Most of the cases the leaves are modified into spines or scales (Casuarina).

Ø   Leaf may modify into phyllode in some plants.

Ø   Phyllode : leaf petiole or rachis modified (flattened) into leaf like organ Example: Acacia.

Anatomical Adaptations of Xerophytes:

Ø   Root hairs are well developed in xerophytes.

Ø   Roots with well-developed root cap.

Ø   In Asparagus, the roots become fleshy and store plenty of water.

Ø   In Calotropis, root cells are with very rigid cell wall.

  (b). Stem

Ø   In succulent xerophytes, the stem possesses water storing regions.

Ø   Epidermis is well developed and with thick walled compactly packed cells.

Ø   Cuticle is very thick and well developed over the epidermis.

Ø   Hypodermis is several layered; often hypodermis will be sclerenchymatous (Casuarina).

Ø   Stomata are present on the stem for gaseous exchange and transpiration.

Ø   Stomata are sunken type and usually situated in pits provided with hairs (Casuarina).

Ø   Vascular tissue is well developed with prominent xylem and phloem components.

Ø   In most of the xerophytes, the bark will be well developed and thick.

Ø  Many oil and resin canals are present in bark.

Ø   Most of the cases, the stem will be photosynthetic and contains chlorenchymatous cells in the outer cortex.

Ø   In the stem of Casuarina, the chlorenchymatous cells are radially elongated and palisade like tissue in appearance.

Ø   Epidermis of the leaf is thick and may be multilayered.

Ø   Thick cuticle present over the outer tangential wall of the epidermal cells.

Ø   In some plants, the epidermal cells can store water.

Ø   In some monocots, some epidermal cells are larger than rest of the cells.

Ø   These cells are called bulliform cells.

Ø   Bulliform cells are motor cells and they assist in leaf rolling to reduce transpiration.

Ø   Hypodermis usually present.

Ø   In Pinus, the hypodermis sclerenchymatous.

Ø   Mesophyll is well developed in xerophytic leaves.

Ø   Many layered palisade tissue present.

Ø   Spongy tissue is less developed in xerophytes with less intercellular spaces.

Ø   Leaves of Aloe have water storing region in the mesophyll.

Ø   Stomata are reduced in numbers and are situated only on the lower sides of the leaves (hypostomatic leaves).

Ø   Stomata are sunken type and usually situated in pits with hairs (Nerium).

Ø   Vascular tissue is well developed with plenty of xylem elements.

Ø   Mechanical tissue well developed in the leaves of xerophytes.

Ø   Transfusion tissue, if present, will be well developed for the lateral conduction.

(3). Physiological adaptations of xerophytes:

Ø   Structural or morphological adaptations of xerophytes are well suited to survive in drought conditions.

Ø   Xerophytic plants are reported to contain pentosan polysaccharides which are reported to offer resistance against drought conditions.

Ø   Many xerophytes show CAM (Crassulacean Acid Metabolism) cycle.

Ø   In CAM plants, the stomata will be closed at day time.

Ø   Stomata open during the night and they absorb enough carbon dioxide for the photosynthesis.

Ø   Absorbed carbon dioxide is converted into malic acid and store in the vacuoles of the cells.

Ø   The malic acid increases the osmotic concentration of cell sap and this enables the closure of stomata in the day time.

Ø   Some enzymes such as catalase and peroxidase are more active in xerophytes.

Ø   Amylase enzyme in xerophytes is more efficient in the hydrolysis of starch than mesophytes.

Ø   Xerophytes can regulate the rate of transpiration.

Ø   They ensure the reduced rate of transpirational loss of water by thick cuticle, distribution of stomata in the lower side of the leaf, sunken type of stomata, and positioning of stomata in pits with many hairs. 

Ø   Xerophytes possess high osmotic concentration of cell sap.

Ø   Thus cells have high osmotic pressure.

Ø   High osmotic pressure increases the turgidity of the cells.

Ø  Turgidity exerts tension force (turgor pressure) on cell wall.

Ø   Due to this high turgor pressure, the wilting of cells is prevented by the extreme heat.

Ø   High osmotic concentration also ensures the rapid and effective absorption of water.

Ø   Tissue of succulents possesses mucilage to hold large amount of water.

Ø   Loss of high proportion of body mass with rapid recovery when water is available.

Ø   Produce brightly coloured, large and showy flowers for attracting pollination agents.

Ø   Cactoid plants produce large amounts of minute seeds.

Ø   Seeds are with thick seed coat for protection.

Ø   Seed surface also possesses mucilage substances to absorb and hold water when it is available.

Ø   Some plants quickly complete their life cycle before the unfavourable conditions.

Ø   Efficient pollination mechanism by moths, bats and birds.

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Essay on Xerophytes | Plants

The below mentioned article provides an essay on xerophytes.

Xeric habitat characterizes xerophytes (xero = dry, phytes = plants). Xerophytes evolved to survive in an ecosystem where there is deficiency in available water. This includes the areas that are subjected to drought like deserts where low rainfall is the norm.

The areas may also include physiologically dry soil (not physically dry) where uptake of water becomes difficult due to salinity in soil water. Therefore xerophytes have evolved a wide variety of adaptations. These adaptations primarily aim to limit water loss, conserve water and obtain water as much as possible from the environment.

Xerophytes have developed the following three main adaptive strategies to survive drought avoidance, drought tolerance and succulence. Each of the adaptations is different but effective against extremely low water availability, desiccating winds, and high and fluctuating temperatures. Different types of plant have these adaptive strategies and among them there exist little morphological, physiological and taxonomical relationship.

The drought avoiding xerophytes are ephemeral-annuals. They live only for a short time period. Germination, growth, flowering, fruiting and dying occur after a heavy rain. These plants tide over drought by the dormant seeds. The seeds germinate only after a heavy rain. Growth occurs and leaves are formed. The leaves remain alive so long water is available.

They wither away after the soil dries out. So these plants remain leafless most of the time. These plants have large and brightly coloured flowers to attract pollinating insects. After fruiting the seeds enter into deep dormancy and thus these plants avoid drought. The drought avoiding plants do not need any xeromorphic adaptations because they have adequate water during their short period of activity.

Mention may be made of the following ephemeral-annuals:

Dithyrea californica, Atriplex pseudocampanulata (completes its life cycle within 70 days), Wahlenbergia communis (completes its life cycle within 36 days), Abronia villosa, Castilleja chromosa (Schrophulariaceae), C. exserta etc. The ephemeral-annuals, more accurately, are to be referred to as simply ‘ephemerals’ because most of them complete the entire life cycle within few months, some in just weeks.

The drought tolerant xerophytes are perennials. They have structural modifications that help them to adapt to the environment.

The roots are very well developed and spread out over a large area to collect maximum water. They may be laterally extensive and shallow. They may be radially elongated. The roots may also be long, vertically deep, e.g. Acacia. Most of the shallow and radial roots are within three feet of the surfaces, e.g. Cactus.

These roots allow quick acquisition, of large quantities of superficial water when it rains. Cacti store water both in root and stem. These plants have adaptations by means of which they can survive years of drought on the water collected from a single rainfall. Prosopis, a drought tolerant plant, develops long vertical deep root systems.

The vertical roots may be as long as 80 feet. These roots draw water from deep underground reservoirs. Some cacti develop special roots after rain to absorb more water. Many xerophytes have both shallow and deep taproots and respectively allow collecting surface water and absorbing water from water table or directly above or below it.

Many xerophytes have root hairs extended to the tip to increase water uptake. The root hairs of many xeric grasses, e.g. Andropogon foveolatus, Panicum turgidum etc. have rhizosheaths. Rhizosheaths are also known as sand grain root sheaths.

The root hairs secrete mucilage where the moving sand grains become attached. The attached sand grains form a sheath around the root hairs. With the increase in number of root hairs the sheath covers the whole root.

The following functions are attributed to rhizosheath:

(1) It is equivalent to cork layer that is formed in dicotyledonous root and prevents the loss of water from inner tissues.

(2) It accelerates water absorption as it contains mucilage that has high absorptive power for water.

(3) It is associated with nitrogen fixation The cortex is usually thin (Fig. 29.1) and therefore there exists small distance between xylem and soil water. The endodermis has wider caspanan bands. So endodermis is more efficient in its function of radial diffusion of water from stele to the cortex.

The xylem is well developed and as a result rapid transport of water occurs following absorption. Xerophytes have evolved methods by means of which they maintain a high osmotic pressure in root tissues. This enables them to increase water absorption. Many cacti accumulate hydrophilic colloids in their root cortex. This reduces the water potential of the root-tissues and thus accelerates the absorption of water by osmosis.

Some members of Juncaceae and many of the Restionaceae show hydromorphic features in the roots and xeromorphic features like abundant sclerenchyma in stems. The roots show air cavities in the cortex like hydrophytes.

This remarkable combination of dual adaptations of hydromorphic roots and xeromorphic stems is probably beneficial to the plant because the stems are sometimes exposed to strong drying winds when the roots become too cold to deliver enough water to meet evaporation losses.

One of the adaptations among the xerophytes is surface reduction. The leaves are very much reduced and absent in many xerophytes. The functions like transpiration and photosynthesis of leaf are surrendered to stem. Such stems grow by marginal growth like leaves and acquire the structure of leaves (ex. Rhipsalis, Ruscus etc.). Such stems are called phylloclades.

The bulbous habit is often associated with xerophytes. In many plants like Narcissus, Scilla, Tulipa, Haemanthus etc. leaves and flowers develop for a limited period in each year. The plants survive through underground stems. Swollen underground stems occur in many species of Asclepiadaceae.

Rhizomes occur in the species of Iris. Corms occur in Crocus, Watsonia etc. The above plants grow actively when water is available. The aerial organ like leaf remains alive so long water is available and withers away when the water is used up. So the aerial organs show little adaptations to xeric condition.

Internal adaptations in xerophytes include – mechanisms to provide for the storage of water and to develop mechanical tissues to resist collapse and tearing on drying.

The plants that are adapted to store water are described as being succulent (ex. many species of Crassulaceae, Aloe etc.). The plants that develop mechanical cells to resist tearing and disruption of tissues as a result of excessive desiccation are usually described as sclerotic (ex. Hakea, Leptocarpus, Ulex etc.).

Stems of woody xerophytes are efficiently insulated by periderm to limit water loss. The tissues of periderm may be lignified and often impregnated with resins. Spines may be present on the surfaces of stem. Many xerophytes have hypodermis, the cells of which are composed of chlorenchyma cells.

These cells, when enclosed in rigid and lined channels, add structural rigidity, e.g. Leptocarpus stem. Hypodermis may also be composed of thick walled cells like fibres and sclereids. These cells may be present as a continuous sheet or in patches. Hypodermal fibres may develop on the peripheral side of thin-walled chlorenchyma, e.g. Ecdeiocolea stem.

Hypodermal sclerenchyma protects the inner tissues from high intensity of light and thus limits the loss of water. It also provides mechanical support. Leafless xerophytes and xerophytes with reduced leaves have palisade like cells in the outer cortex. These cells are compactly arranged and compose the photosynthetic tissues, e.g. Casuarina (Fig. 29.2).

Xerophytes have well-developed vascular tissues with long xylem vessels. The tracheids have relatively thicker walls than those present in mesophytes. Annual rings are well developed. Wood of many xerophytes is ring porous. The conduction through this wood is ten times more than diffuse porous wood. In Pinus, oils and resins are produced. Latex develops in Euphorbia.

Leaf polymorphism is observed in many xerophytes. After heavy rain broad leaves are formed and narrow leaves follow when the soil dries out. Xerophytes have evolved mechanisms to limit water losses. Loss of water is due to transpiration from exposed aerial parts. The size of the transpiring surface determines the amount of water loss.

The smaller is the surface usually the lower is the transpiration. The reduction of transpiring surface can be accomplished in the following ways. The twigs, branches and mature leaves may be shed during drought. The plant-core remains alive. Immature leaves are more resistant to drought than mature leaves. So the former is seldom shed.

The leaves may be long, slender, dissected or greatly reduced to spines. The scale or needle-like leaves are common in Coniferae and Ericaceae. Leaves with reduced surface are noted in Calluna, Thuja and Asparagus. Such leaves are called microphylly. Leaves are entirely absent in some Cactaceae, Asclepiadaceae and Euphorbiaceae.

Most Restionaceae have non-functional leaves. During midday sun small and narrow leaves heat up less rapidly than larger ones. As a result transpiration decreases. The long, slender leaves are usually vertically oriented to reduce the amount of heat absorbed. Plants reduce the exposed surface to sun or drying winds by rolling or folding of leaves.

Plants also achieve this by rotating and orienting leaves away from maximum exposure to wind or sun. The leaves of xeromorphic species of Stipa and Ammophila remain folded constantly thus hiding the stomata. Ammophila arenaria (Fig. 29.3) leaf entirely rolls up towards the upper surface where stomata are located thus reducing the surface of moist tissue that is exposed to air and enclosing the stomata when dry condition prevails.

In many xeromorphic species dead hairs or hair-like projections cover the leaf surface and they form an insulating layer, e.g. Artemisia, Kleinia, Elaeagnaceae etc. Such structures are called trichophyllous. Such leaves are gray or white owing to the hair covers. The white colour aids in deflecting heat from leaves.

Moreover leaf hairs provide shade to leaves. It is interpreted that hairs create pockets on the leaf surface where water vapour accumulates. As a result the diffusion of water from the leaf is reduced. Most xerophytes have hairs that have thickened walls and some also have thick cuticle.

These hairs, e.g. Gahnia, Ammophila and Erica reduce water losses in contrast to thin-walled hairs that increase water loss under some conditions. Moreover hairs are good deterrents against insect feeding and egg laying. Hairs also give protection against predator when plants become the only source of moisture for animals during drought.

Transpiration may be cuticular or stomatal. The magnitude of cuticular transpiration is governed by the formation of cuticle and cuticular layers. Many xerophytes such as Cactaceae have a heavy cuticle and thick cuticular layers.

These cuticular layers almost entirely arrest the cuticular transpiration. Leaves are also covered with lipids to reduce moisture evaporation (ex. Ricinus, Calotropis etc.). Due to the presence of cutin and lipids the two epidermises of a leaf become impervious to water loss.

The thickness of cuticle is related to xeric conditions. In a study it is observed that Prosopis velutina, when grown in natural xeric condition, have cuticle ten times thicker in comparison to that grown in indoors.

Transpiration is a vital process in all plants. When the water potential inside a leaf is higher than the environment, the water vapour will diffuse out of the leaf. If a plant loses too much water, wilting will result. In case of permanent wilting plants will die. So the xeromorphic leaves have adaptations that decrease the water potential in order to reduce water loss.

The functioning and position of stomata govern the magnitude of stomatal transpiration. In many xeromorphs stomata open for a brief period only. In others stomata remain closed in the day. They open at night (ex. Camellia thea) when the relative humidity is high and temperature is low. As a result there is less transpiration.

Usually xeromorphs have well developed and often numerous stomata. It is interpreted that carbon dioxide enters rapidly through these stomata during rare wet periods. Xeromorphic leaves may be epi- or hypostomatic. The stomata are often protected to restrict water loss. An individual stoma may be sunken (ex. Aloe).

In Nerium oleander groups of stoma occur in a groove or depression on the abaxial surface of leaf (Fig. 29.4). The surface of groove is lined with hairs. In the groove the relative

humidity always remains high thus reducing the diffusion gradient within the chamber. This reduces evaporation of moisture.

In Ficus, Nerium etc. the stomata are restricted to well-protected crypts to reduce water loss. In Agave (Fig. 29.5), Dasylirion etc. cuticle forms ridges inside the pore of a stoma. Thus the canals that communicate between open air and intercellular space become narrower. As a result water loss is reduced.

Multiseriate epidermis occurs in Ficus elastica and Nerium. In mature leaves sometimes it is difficult to distinguish a multiple epidermis and a hypodermis. This structure reduces evaporation of water through epidermis and diminishes the intensity of light that reaches the photosynthetic tissue.

Xeromorphic leaves, like many mesophytes, have mesophyll differentiated into adaxial palisade and abaxial spongy tissue. But the palisade mesophyll is well developed and it is often correlated with high light intensity. Though the palisade mesophyll is typically adaxial, they may occur on abaxial side also, e.g. Nerium, Ficus, Atriplex portulacoides, Artemisia, Myoporum, Sonneratia Alba etc.

In these leaves spongy tissue occurs in between the adaxial and abaxial palisade tissue. In many xeromorphs the mesophyll palisade replaces spongy tissue where the leaves have palisade mesophyll only, namely Greggia camportum, Sphaeralcea incana etc. Due to the loss of spongy mesophyll, the palisade parenchyma becomes smaller and packed together.

As a result the volume and surface area of leaf apoplast diminish. So each cell loses less water to the apoplast. The mesophyll cells of Pinus have peg-like ingrowths (plicate) to increase the surface of photosynthesis. Xeromorphic leaves have larger bundles of vascular tissues as compared to mesophytes.

Drought-resistant leaves are hard and rigid. This structure is called sclerophylly. Sclerophylly prevents leaf tissues from mechanical deformation during shrinkage. Thick cuticle occurs on the epidermises. As a result the leaves become leathery with a hard and glossy surface. The tissues of scleromorphic leaves are small-celled and dense.

The palisade mesophyll may be multiseriate. The spongy tissues have little intercellular spaces. Development of sclerenchyma is very common. The hypodermis of Pinus needle is composed of sclerenchyma. In many leaves lignification occurs in mesophyll. In Stipa, the major part of the leaf tissue is composed of sclerenchyma.

The abaxial epidermis of Ammophila arenaria is without stomata and lignified as the major portion of mesophyll. The collenchyma cells are restricted to small strands. Sclerenchyma provides mechanical support to the leaves and protects the inner tissues from high intensity of light. Thus loss of water is reduced. The thickening of cell wall is caused by the conversion of polysaccharides into celluloses and other materials.

Succulence in stems and leaves is common within xerophytes. The succulent organs thicken due to water storage. The succulent stem may attain a spherical shape, e.g. Mamillaria. A sphere has the smallest surface area in relation to tissue volume. So by increasing the thickness of an organ the relative surface is reduced. The surface reduction is favourable for the water balance.

Succulent stems have little differentiation of ground tissue. Parenchymatous spherical cells compose the ground tissue. Stem succulence occurs as a result of proliferation of xylem parenchyma and by primary thickening growth, e.g. Cactaceae. The mechanical tissue and vascular tissue are poorly developed.

The cell walls are often mucilaginous. The succulent leaves, also referred to as malacophyllous xerophytes, are similar on all sides. The epidermis of such leaves is multilayered, large-celled and occupies the major portion to the leaf volume e.g. Begonia, Zebrina (Fig. 29.6), and other members of Commelinaceae Piperaceae etc.

It is interpreted that the water present in these layers protects the central mesophyll against water losses during dry periods. The succulent leaves of Aloe and Haworthia have epidermis with thick outer walls. The epidermis has cuticle and cuticular waxes. The stomata are sunken. In Aloe, the stoma (Fig. 29.7) is variously protected thus regulating and minimizing water loss during dry periods.

Above each stoma there is raised rim that forms a suprastomatal cavity. The cavity has a constricted opening to the atmosphere. It is interpreted that during favorable conditions of growth the cavity has a role in enhancing evaporation. Due to the presence of narrow opening in the cavity the structure has a venturi effect that lowers pressure above the stoma and assists transpiration.

Some leaves, e.g. Haworthia and Lithops have characteristic features. The leaves have chlorenchyma and water storing mesophyll. The leaf tips are translucent. The leaves remain underground, the tips being above the ground level only. The photosynthetic tissues perceive the light stimulus through the cells present on the leaf tips. These are often referred to as ‘window plants’.

In succulent leaves the vascular tissues are poorly developed. The mechanical cells are also scanty. Most of the succulent species fix carbon dioxide in the dark. The stomata of such plants remain closed during day. The stomata open at night. During high temperature the stomata may also remain closed at night when carbon dioxide exchange becomes nil.

Such plants survive by fixing carbon dioxide made available internally through respiration. These plants have adapted a specialized photosynthetic process, called Crassulacean Acid Metabolism (CAM). Plant having Crassulacean Acid Metabolism is referred to as CAM plant. In this plant carbon dioxide is fixed through phosphoenolpyruvate in the dark.

Phosphoenolpyruvate carboxylase catalyzes the carboxylation. As a result oxaloacetic acid is formed. It is then reduced to malate. During daytime malate is decarboxylated. The released carbon dioxide is fixed in ribulose-1, 5-bisphosphate and enters the Calvin cycle. Ribulose-1, 5-bisphosphate carboxylase catalyzes the reaction.

These plants have sufficient ribulose-1, 5-bisphosphate carboxylase activity. CAM plants can exist for long periods without any carbon dioxide uptake in light. CAM plants are adapted to store carbon dioxide in malate during night. Carbon dioxide is made available during day when malate is decarboxylated.

Plants belonging to the family Crassulaceae have CAM. The term CAM derives from the family name. Certain members of other families like Bromeliaceae, Euphorbiaceae, Aizoaceae, Liliaceae etc. also exhibit CAM.

Many xerophytes have an alternative pathway of photosynthetic carbon fixation in contrast to Calvin cycle that operates in mesophyte. This alternate pathway is known as Hatch-Slack pathway or C 4 -dicarboxylic acid pathway or simply C 4 -pathway. Plants having this pathway are referred to as C 4 -plants. This pathway is characterized by the formation of dicarboxylic acids of 4-carbon compounds as primary products of photosynthesis in contrast to 3-carbon compounds of the Calvin cycle.

The chloridoid—eragrostoid and panicoid taxonomic divisions of the Gramineae, Centrospermae, Compositae, Euphorbiaceae etc. carry out photosynthesis by using Hatch-Slack pathway. These plants have specific type of anatomy, referred to as ‘Kranz’ anatomy. Kranz is a German word—meaning garland or wreath.

In this type specialized bundle-sheath cells surround the vascular bundles of leaf. Chlorenchyma cells encircle the bundle-sheath. These radially aligned chlorophyllous mesophyll cells were given the German name ‘Kranz’. The cells of bundle-sheath contain large chloroplasts and starch.

The essence of Hatch-Slack pathway is that C 4 -compounds carry carbon dioxide from mesophyll cells to bundle-sheath cells where photosynthesis occurs. The C 4 -pathway starts (Fig. 29.8) in the mesophyll cells for the transport of carbon dioxide. Carboxylation occurs in the mesophyll cells where carbon dioxide and its receptor phosphoenolpyruvate condense to transient 4-carbon compound—oxaloacetate.

The enzyme phosphoenolpyruvate carboxylase catalyzes the condensation. Oxaloacetate is rapidly reduced to malate or aminated to aspartate depending upon species. C 4 -compounds, formed in the mesophyll, enter into bundle-sheath cells where they are decarboxylated. The released carbon dioxide enters the Calvin cycle.

Pyruvate formed during decarboxylation returns to the mesophyll cell for another round of carboxylation. It is to note that the decarboxylation of the C 4 -compounds in the bundle-sheath cells maintains a high concentration of carbon dioxide at the site of photosynthesis.

In Calvin cycle carboxylation occurs by the condensation of carbon dioxide and ribulose-1, 5-bisphosphate to form a transient 6-carbon compound, which rapidly hydrolyzes to two molecules of 3-phosphoglycerate. Ribulose-1, 5- bisphosphate carboxylase catalyzes the condensation.

RibuIose-1, 5-bisphosphate carboxylase is also an oxygenase when it catalyzes the addition of oxygen to ribulose-1, 5-bisphosphate to form phosphoglycolate and 3-phosphoglycerate. The oxygenase and carboxylase reactions occur at the same site and compete with each other. Under normal atmospheric conditions at 25°C the rate of carboxylase activity is four times greater than oxygenase.

In higher temperature and when there is high oxygen and low carbon dioxide the Ribulose-1, 5-bisphosphate carboxylase switches to oxygenase activity. This enzyme catalyzes the oxygenation of Ribulose-1, 5-bisphosphate thus forming phosphoglycolate and 3-phosphoglycerate.

The recycling of phosphoglycolate leads to the release of carbon dioxide and consumption of oxygen in a process called photorespiration. It is interpreted that photorespiration is seemingly a wasteful process because the organic carbon is converted to carbon dioxide without the production of adenosine triphosphate (ATP).

Xerophytes have evolved method to minimize the wasteful reaction of photorespiration. They have adapted C 4 -pathway. This pathway maintains a high concentration of carbon dioxide in the bundle-sheath cells at the site of Calvin cycle.

This accelerates the carboxylase reaction of Ribulose-1, 5-bisphosphate carboxylase in relation to oxygenase reaction. Thus the C 4 -plants take advantage of high temperature and minimize the oxygenation of Ribulose-1, 5-bisphosphate.

Plants growing on the mountainous parts have xeromorphic adaptation, e.g. Pycnophyllum molle and P. micronatum etc. belonging to the family Caryophyllaceae. They have cylindrical stems and very much reduced leaves. Stomata are present only on the adaxial surface and they are sunken and protected amongst papillae.

But the species like Oxalis exidua show little xeromorphic adaptation. In O. exidua the stomata are superficial; hairs and papillae occur on the epidermal surface. The chlorenchymatous mesophyll cells are not compact. The leaves have all the characteristics similar to those of the mesic members of the genus.

But the anatomy of stem have characteristic of a liana. The vascular bundles are separate. During secondary growth the interfascicular cambium produces parenchyma only instead of secondary xylem and phloem. By this device the stem can twist and deform without compressing the vascular bundles when the stem penetrates the cracks between rocks.

Azorella compacta, another plant growing on mountainous environment, has very shiny leaves. The shiny leaves reflect ultraviolet light. The plant possesses contractile roots, which help the plant to be firmly anchored in the frost heave. Many plants growing in mountainous environment have sap that is mucilaginous nature. This acts as a kind of antifreeze.

Halophyte often shows xeromorphic adaptations. They grow on locations with a high content of salts that make the soils entirely sterile. Many halophytes exhibit succulence that is normally associated with drought. The leaf area is strongly reduced, e.g. Salsola, Glaux, Mesembryanthemum etc. In some plants leaves are absent, e.g. Salicornia.

The succulent leaves have salt glands through which excretion of salt occurs. Salt gland regulates the salt content of plants and prevents salts accumulating in the protoplasm. Moreover salt glands protect the leaves against strong sunlight and insect feeding.

Succulence and hard-leaf characters are combined in the tree and shrubby species of halophytes. The leaves have thick cuticle and the palisade tissue is many layered. The mesophyll tissue is weakly differentiated.

Related Articles:

• Xerophytes: Categories and Physiological Adaptation of Xerophytes | Plant Adaptation
• Differences between Photophilous and Sciophilous Plants | Plants
• Occurrence and Position of Stomata in Epidermis | Plants
• Xerophyte: Meaning and Characteristics | Plants | Botany

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Xerophytes, xeromorphs and sclerophylls: the history of some concepts in ecology

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G. SEDDON, Xerophytes, xeromorphs and sclerophylls: the history of some concepts in ecology, Biological Journal of the Linnean Society , Volume 6, Issue 1, March 1974, Pages 65–87, https://doi.org/10.1111/j.1095-8312.1974.tb00714.x

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Research on xeromorphic and sclerophyllous (the literal meanings of which are “dry-form” and “hard-leaved”) plants offers a case-history illustrating the nature of “progress” in one branch of science. The story runs from about 1890–1970, beginning with the birth of ecological concepts, including Warming's 1895 classification of plants into hydrophytes, xerophytes and meso-phytes, Schimper's pioneer work on the sclerophylls, and with the conceptions that lay behind this work; and so on through the main lines of research, concluding with an account of work on the “anomalous” distribution of the sclerophylls in Australia. This case-history shows how the problems of classification and categorization may be linked to conceptual and empirical problems of substance, and hence are not “merely” classificatory. Indeed, the hypotheses under test are not formulated explicitly, but are encapsulated in the terminology, as is so often the case in the biological sciences.

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Introduction to Xerophytes (A-level Biology)

Introduction to xerophytes, xerophytic plants.

• Xerophytic plants are adapted to living in hot, dry environments . Xerophytes live in very hot and dry conditions, so need to be adapted to minimise water loss. An example of xerophytes are cacti .
• Xerophytes need to minimise transpiration . Due to the heat of the environment, and low water vapour in the air, the risk for losing water through transpiration is very high in xerophytes.
• Xerophytes have developed several adaptations to survive :

Xerophytes are plants that have adapted to living in dry and arid environments. These plants have developed special structures and adaptations that allow them to survive in areas where water is scarce.

Table of Contents

Xerophytes have several adaptations that help them survive in dry environments. These include: Deep roots: Xerophytes have deep roots that can reach underground water sources. Reduced leaves: Xerophytes often have small, reduced leaves that minimize water loss through transpiration. Waxy or hairy surfaces: Some Xerophytes have waxy or hairy surfaces that reduce water loss by limiting the amount of air that comes into contact with the plant’s surface. Storing water: Some Xerophytes store water in their stems, leaves, or roots to use during dry periods. Adaptive leaf structures: Some Xerophytes have adaptive leaf structures, such as spines, that reduce water loss and help protect the plant from herbivores.

Xerophytes are found in a variety of dry and arid environments, including deserts, semi-deserts, and Mediterranean climates. They are also found in areas where water is scarce, such as rocky outcrops, dry river beds, and coastal dunes.

Some examples of Xerophytes include cacti, succulents, aloes, and agave plants. These plants are well adapted to dry environments and have evolved a range of strategies to survive in these conditions.

The study of Xerophytes is important for A-Level Biology students as it provides a fundamental understanding of the adaptations that plants have developed to survive in dry environments. Understanding the adaptations of Xerophytes can help students to understand how plants are able to survive in extreme environments, and this knowledge can be applied to other areas of biology, such as the study of plant physiology and ecology. The study of Xerophytes also provides students with an opportunity to develop their scientific observation skills, as they can observe and study the unique structures and adaptations of these plants in detail.

Xerophytes play an important role in the ecosystems in which they live. They help to stabilize the soil and provide habitat for a range of other species, such as birds, reptiles, and insects. Xerophytes are also an important source of food and water for many species, and they play a crucial role in maintaining the balance of these ecosystems.

Yes, Xerophytes have a range of commercial uses, including as ornamental plants, for food and medicine, and for the production of oils, dyes, and other products. Many Xerophytes are also used for landscaping and horticulture, as they are well adapted to dry conditions and can be grown in areas where water is scarce.

The study of Xerophytes can contribute to conservation efforts by providing a better understanding of the adaptations that plants have developed to survive in dry environments. This knowledge can be used to develop strategies for preserving these plants and their habitats, and to prevent the loss of these important species.

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Xerophyte: Meaning and Characteristics | Plants | Botany

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In this article we will discuss about:- 1. Meaning of Xerophyte 2. Types of Xerophytic Plants 3. Characteristics of Xerophytes 4. Ecological Adoptation 5. Anatomical features.

• Anatomical features of Xerophyte

1. Meaning of Xerophyte:

A xerophyte (xero meaning dry, phyte meaning plant) is a plant which is able to survive in an environment with little availability of water or moisture. Plants like the cacti and other succulents are typically found in deserts where low rainfall is the normal phenomen, but few xerophytes can also be found in moist habitats such as tropical forests, exploiting niches where water supplies are limited or too intermittent for mesophytic plants.

Plants that live under arctic conditions may also have a need for xerophytic adaptations, as water is unavailable for uptake when the ground is frozen. Their leaves are covered with silvery hairs.

Adaptations of xerophytes include reduced permeability of the epidermal layer, stomata and cuticle to maintain optimal amounts of water in the tissues by reducing transpiration, adaptations of the root system to acquire water from deep underground sources or directly from humid atmospheres and succulence, or storage of water in swollen stems, leaves or root tissues. The typical morphological consequences of these adaptations are collectively called xeromorphisms.

2. Types of Xerophytic Plants :

These are plants adapted to grow in dry habitats.

They are classified into four categories on the basis of their morphology and life cycle pattern:

a. Ephemeral Annuals:

These plants are also called as drought evaders or drought escapers. They are annuals and complete their life cycle within a very short period. They do not withstand dry seasons but actually avoid them. Argemone mexicana, Solatium xanthocarpum.

b. Succulent:

These plants grow in habitats with less or no water. They store water whenever it is available. They have succulent and fleshy organs like stems, leaves and roots which serve as water storage organs and accumulate large amounts of water during the brief rainy seasons. Euphorbia and Opuntia.

c. Non-Succulent Perennials:

These are drought resistant and called as true xerophytes. They possess a number of morphological, anatomical and physiological characteristics which enable them to withstand critical dry conditions. Calotropis, Acacia, Casuarina and Nerium

d. Succulent Plants:

Succulent plants typically store water in stems or leaves. They include the Cactaceae families which typically have stems that are round and store a lot of water. Often, as in cacti where the leaves are reduced to spines, their leaves are vestigial, or they do not have leaves.

3. Characteristics of Xerophytes:

(i) Reduction in Air Flow:

Some xerophytes have tiny hairs on their surface to provide a wind break and reduce air flow, thereby reducing the rate of evaporation. When a plant surface is covered with tiny hairs, it is called tomentose. In a still environment, the areas under the leaves/spines where transpiration is taking place form a small localized environment that is more saturated than normal with water vapour.

If this is not blown away by wind, the water vapour potential gradient is reduced and so is transpiration. Thus, in a windier situation, this localization is not held and so the gradient remains high, which aids the loss of water vapour. Spines trap a layer of moisture and also slow air movement over tissues.

(ii) Reflectivity :

The color of a plant, or of the waxes or hairs on its surface, may serve to reflect sunlight and reduce evaporation. An example is the white chalky wax (epicuticular wax) coating of Dudleya brittonii, which has the highest ultraviolet light (UV) reflectivity of any known naturally occurring biological substance.

(iii) Physiological :

Some plants can store water in root structures, trunk structures, stems, and leaves. Water storage in swollen parts of the plant is known as succulence. A swollen trunk or root at the ground level of a plant is called a caudex and plants with swollen bases are called caudiciforms. Tiny pores on the surface of a xerophytic plant called stomata may open only at night, so as to reduce evaporation.

Plants may secrete resins and waxes (epicuticular wax) on their surfaces, which reduce evaporation. Examples are the heavily scented and flammable resins (volatile organic compounds) of some chaparral plants, such as Malosma laurina, or the chalky wax of Dudleya pulverulenta.

Plants may drop their leaves in times of dryness (drought deciduous), or modify the leaves produced so that they are smaller.

During dry times, xerophytic plants may stop growing and go dormant, change the kind of photosynthesis or change the allocation of the products of photosynthesis from growing new leaves to the roots.

ADVERTISEMENTS: (adsbygoogle = window.adsbygoogle || []).push({}); 4. Ecological Adoptation in Xerophytes:

1. Plants growing in habitats where water supply is absent or physiologically dry are called Xerophytes.

2. Xerophytes classified based on their (a) Morphology (b) Physiology (c) Life cycle pattern

3. Plants growing in dry or arid zones are called Ephimerals or Drough evaders or drought escapers. Eg; Tribulus

4. Ephemerals are Annuals and complete their life cycles in 6-8 weeks.

5. Xerophytic plants absorbing more water during rainy season and storeing them in different body parts are called Succulents or drought avoiding plants.

6. Succulents store water in the form of mucilage.

7. Leaf succulents: Bryophylum, Aloe, Agave.

8. Root succulents: Asparagus

9. Perennial plants which can withstand prolonged period of drought are called Non-succulents or true xerophytes Eg: Casurina, Nerium, Ziziphus, Calotropis etc.

10. Ecological adaptations of Xerophytes.

11. The all three major groups of xerophytes have some common adaptations to survive in very dry conditions.

1. Root system is very well developed with extensive branching and often longer than shoot system.

2. Root hairs and root caps are very well developed.

1. Mostly they are stunted, woody hard and covered with thick bark.

2. In some xerophytes stem becomes underground.

3. In some plants stem becomes fleshy, green, leaf-like phylloclades covered with spines, Eg: Opuntia.

4. Stems are usually covered by hairs and or waxy coatings.

1. Leaves are very much reduced small scale like and sometimes modified in to spines to reduce the rate of transpiration. Lamina may be long narrow needle-like or divided in to many leaflets as Eg: Acacia.

2. Foliage leaves become thick fleshy and succulent or tough and leathery in texture. Eg: Aloe.

3. Leaf surfaces are shiny glazed to reflect light and heat. Eg. Calotropis.

5. Anatomical features of Xerophyte:

1. Epidermis is covered thick cuticle to reduce the rate of transpiration.

2. Epidermal cells may have silica crystals.

3. Epidermis is multilayered Eg: Nerium.

4. Waxy coating is present on leaves and stem Eg: Calotropis.

5. Stomata are generally confined to lower epidermis of leaves called hypostomatous.

6. Stomata are present in pits called sunken stomata. They are lined with hairs Eg: Nerium.

7. Mesophyll is differentiated in to palisade and spongy parenchyma.

8. Mechanical & vascular tissues are well developed.

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Difference between Hydrophytes, Mesophytes and Xerophytes

Based on their water requirements and adaptations, plants are divided into three major groups: (1) Hydrophytes, (2) Mesophytes, (3) Xerophytes and. Let us throw some light on the three types, hydrophytes, mesophytes and xerophytes and differentiate between them.

Hydrophytes

Plants that are adapted to live in aquatic environments are called hydrophytes. They might be fully submerged, partially submerged or floating in water. These plants have special adaptations that help them to survive in water.

All the aquatic plants have a spongy tissue that creates air spaces in stems, roots as well as leaves that allows exchange of air and other gases in the plant. They have floating leaves with long, fine and dissected petioles to prevent flooding of water. Stomata is absent in completely submerged plants and xylem vessels are poorly developed.

Example: Vallisneria and Hydrilla are totally submerged hydrophytes. Eicchornia and Azolla are floating hydrophytes. Ranunculus and Alisma are partially submerged hydrophytes.

A majority of plants living on this planet are mesophytes. These are the plants that can survive in moderate environments that are neither particularly dry nor particularly wet. They thrive in soil that is not swamped in water and has moderate salt content and humidity.

They have well differentiated roots and shoots with a fully developed vascular system. They do not need any adaptations to survive. They have an exposed stomata on leaves that are flat, broad and green. They require moderate to less amounts of water. They grow fast and usually large. Their leaves have a cuticle with thin epidermis .

Example: corn, rose, clover, squash, etc.

Plants that are adapted to survive in physiologically dry conditions are called xerophytes. They have special adaptations to prevent loss of water, and also store some water. Plants that store water are called succulents, e.g, cacti, agave. They have thick and fleshy stems that are able to store water. This water can be used whenever required.

Other adaptations in xerophytes include waxy coatings on leaves, dropping leaves during dry periods, folding or repositioning of leaves for sunlight absorption and hairy coverings on leaves.

Other examples of xerophytes include pineapple, Acacia , prickly pear and alfalfa.

Hydrophytes vs Mesophytes vs Xerophytes

Explore BYJU’S Biology for more related topics.

• What is Physiological Adaptation? An Overview
• Plant & Animal Adaptations
• Animal Habitats – Everything You Need to Know

Frequently Asked Questions

What is the difference between xerophytes and halophytes.

Xerophytes are plants that can survive in physiologically dry conditions, whereas halophytes are plants that can survive in high saline environments.

What is the difference between xerophytes and epiphytes?

Xerophytes are plants that can survive in extremely dry conditions, whereas epiphytes are plants that grow on other plants for support.

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Xerophytic Plant Leaf Adaptations ( CIE A Level Biology )

Revision note.

Biology Lead

Xerophytic Plant Leaf Adaptations

• Xerophytes (from the Greek xero for ‘dry’) are plants that are adapted to dry and arid conditions
• Xerophytes have physiological and structural (xeromorphic) adaptations to maximise water conservation

Xeromorphic features table

Photomicrograph and annotated drawing showing the xeromorphic features of a leaf of Ammophilia arenaria (Marram grass)

Remember not all leaves will have every feature listed above so if you are looking at an unfamiliar image consider whether the adaptations you can see will help reduce water being lost from the leaf.

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