Anatomical features of xerophytic plants

Xerophytes are plants which grow in xeric environment. They have adapted morphological, physiological and anatomical changes in order to survive in xeric conditions. Various anatomical adaptations in xerophytic plants which helps to absorb as much as water as possible, to store for long time and to reduce the rate of transpiration which enables them to survive in xeric condition are included in the presentation.

1. Anatomical features of xerophytic plants Presented by: Megha Varshini Gowda B R

2. Contents Introduction Anatomical features in Xerophytic root. Xerophytic stem. Xerophytic leaves. Conclusion References

3. Introduction Eugenius Warming (1909) classified plant communities as hydrophytes, mesophytes and xerophytes. Xerophytes are plants which grow in xeric environment. Xerophytes are generally classified as: Plants growing under xeric condition become adapted structurally and physiologically to habitats. Morphological adaptations includes well developed root system, modification of stem into cladode and phylloclades , leaves are sclerophyllous , microphyllous , trichophyllous or sometimes caducous .

4. Anatomical features seen in xerophytic roots Presence of suberised exodermis - regulates the inverse flux of water. Water storage parenchyma cells in cortical region. Fig.1: Suberised exodermis in Primula palinuri petagna . Fig.2: Water storage parenchyma in Asparagus acutifolius .

5. Presence of additional layers of cells with thickened walls around the stele and lignified pith in Asparagus acutifolius . Endodermis with thickened cell walls and additional layers of thick walled cells around stele in Lygeum spp. Fig.3: Additional thick walled layer of cells and lignified pith in Asparagus acutifolius . Fig.4: Endodermis with thickened cell walls in Lygeum spp.

6. Adaptation Function Example Suberised exodermis Regulates reverse flux of water. Primula palinuri Parenchyma in cortex Stores water Asparagus acutifolius Additional layer of thick walled cells around stele Prevents desiccation Asparagus acutifolius Thick walled endodermis Regulates reverse flux of water. Lygeum spp Table.1: Summary of xerophytic adaptations in roots.

7. Anatomical features seen in Xerophytic stems Epidermis It is well developed with thick walled cells. Thick cuticle gets deposited on the outer surface of the cells. Deposition is multilayered in Capparis stem. The thickness of deposition is directly proportional to the xeric conditions. Fig.5: Cuticle layer.

8. Epidermal hairs Multicellular epidermal hairs made up of rectangular cells, apical cell is rounded and slightly bulbous are present in Bougainvillea stem. Epidermal hairs in case of Casuarina stem arises from base of furrow and each trichome is sickle shaped consisting of 2 basal cells and a long thick walled terminal cell. Fig.6: Multicellular trichomes in Bougainvillea stem Fig.7: Trichomes arising from furrows in Casuarina stem.

9. Hypodermis It is well developed and is made up of several layers of thick walled cells It is composed of collenchyma cells or sclerenchyma cells. In Casuarina , T-shaped sclerenchymatous hypodermis is found below the ridges. Stomata are sunken, if present. Xylem and phloem are well developed. Fig.8: Sclerenchymatous hypodermis below ridges of Casuarina stem.

10. In succulent xerophytes, the ground tissue of stem is made up of thin walled parenchyma cells. These cells preserve excess of water and mucilage in them and therefore the stem is fleshy. Fig.9: T.S of stem of Euphorbia tirucalli .

11. Modification of stem Phylloclade Stem becomes flattened, grean and leaf-like and performs photosynthesis. Shows nodes and internodes. Sunken stomata present on both sides. Thick sclerenchymatous patches –uniformly distributed above each vascular bundle. Scelenchymatous patches are present at the two corners. Well developed layers of palisade on both sides. Fig.10: Phylloclade of Muehlenbeckia platyclada . Fig.11: V.S of phylloclade of Muehlenbeckia platyclada .

12. Cladode Modification of stem in which a branch of single internode is flattened and becomes leaf-like. The proper leaf is reduced to a scale in the axil of which develops a group of linear, narrow structure called cladode. The epidermis is covered externally by a thick cuticle. The palisade and spongy cells contain abundant chloroplasts. Stomata are few in number as a check against transpiration. Fig.12: A part of a cladode of Asparagus asparagoides . Fig.13: Internal structure of cladode.

13. Adaptation Function Example Thick cuticle Protection against desiccation Capparis spp. ( multilayerd cuticle) Trichomes Maintains humid air around stomata Bougainvillea Casuarina (sickle shaped) Sclerenchymatous hypodermis Protects internal tissue from high light intensity. Casuarina spp. Thin walled parenchyma Preserve excess of water and mucilage Euphorbia tirucalli Modifications: 1.Phylloclade Sunken stomata Sclerenchyma surrounds vb Reduces transpiration Muehlenbeckia platyclada . 2. Cladode Well developed palisade cells Increase in photosynthetic activity Asparagus asparagoides Table.2: Summary of xerophytic adaptations in stem.

14. Anatomical features seen in xerophytic leaves The organ that is most strikingly modified in xerophytes is the leaf. Epidermis Cells are small but compactly arranged. It is single layered with thick walls. Occasionally epidermis is multilayered- may be on the dorsal surface( Ficus ) or on both the surface( Nerium ). Fig.14: Additional layers of epidermis in Nerium oleander L.

15. Bulliform cells Certain grass leaves have motar cells which play major role in rolling of the leaves during the period of dryness. These cells are thin walled, greatly enlarged and sensitive to turgor changes. When these are turgid, leaf remains flattened and when flaccid, the lamina rolls and minimize the exposure of transpiring surface. Fig.15: Bulliform cells in Zea mays L.

16. Stomata Stomata are of sunken type. Reduction of transpiration is of utmost importance and it is possible only if the stomata number per unit area is reduced or if the stomata are elaborately modified in their structure. Walls of guard cells and subsidiary cells are heavily cutinised and lignified. The stomatal cavities are often provided with stomatal hairs. In certain desert plants, such as Capparis spinosa and Aristida ciliata stomata may sometimes get blocked due to deposition of resinous matter or wax. Fig.16: Sunken stomata in Yucca sp.

17. Mesophyll tissue Well developed and differentiated into compactly arranged palisade tissues and loosely arranged spongy tissue. Palisade parenchyma is usually present towards dorsal surface and are arranged in a single layer. In Nerium , Ficus and Atriplex , palisade is present on both adaxial and abaxial surfaces and spongy tissues lie in between the palisade layers. Fig.17: Palisade layer in both abaxial and adaxial surface of Nerium leaf.

18. Vascular tissues are well developed and are differentiated into xylem with lignified elements and phloem. In addition to central vascular bundle in the midrib region, there are several other vascular bundles too as seen in Nerium . Presence of cystolith , a deposition of calcium carbonate in certan cells of the upper epidermis can be seen in Ficus bengalensis leaf . Mechanical tissues are well developed, including several kinds of scelreids .

19. In certain non succulent xerophytes ( Ammophila , Agropyron ) leaves become rolled and folded in such a way that stomata occupy the hidden position, thus minimizing the rate of transpiration. Fig.18: Cross section of rolled/folded leaves of Ammophila arenaria . Fig.19: A part enlarged.

20. Modification of leaves Phyllode Petiole gets modified to form a flattened and leaf-like structure in Acacia auriculiformis . Epidermis is covered by thick cuticle, partially sunken stomata are present in lower epidermis. Palisade is well developed and present on both surface. Massive sclerenchyma surrounds the bigger central bundle and form a cap-like structure over the smaller corner bundles. Fig.21: T.S of phyllode of Acacia auriculiformis . Fig.20: Phyllode of Acacia auriculiformis .

21. Adaptation Function Example Multilayered epidermis with thick cuticle Reduces transpiration rate Ficus (dorsal surface) Nerium oleander L.(both the surface) Bulliform cells Rolling of leaves to minimize exposure of transpiring surface. Zea mays L Sunken stomata Reduction of water loss during transpiration Capparis spinosa Well developed palisade cells Minimise direct penetration of light Ficus , Atriplex Several vascular bundles Nerium oleander L. Rolled/folded leaves Maintain humid air around stomata Ammophila arenaria Modification- Phyllode Sunken stomata Reduces transpiration Maintain humid air around stomata Acacia auriculiformis Table.3: Summary of xerophytic adaptations in leaves.

22. Conclusion Plants which are adapted to grow in scarcity of water are called as xerophytes. They have adapted morphological, physiological and anatomical changes in order to survive in xeric conditions They develop certain anatomical adaptations to absorb as much as water as possible and to retain it in their organs for long time and to reduce the rate of transpiration which enables them to survive in xeric condition.

23. References Pandey , S.N and Chadha , A.1996. Plant anatomy and embryology. Vikas Publications, New Delhi. Shukla , R.S and chandel , P.S.2000. Plant ecology and soil science. S Chand Pub. Subrahmanyam , N.S and Sambumurty A.V.S.S.2006.Ecology.2 nd ed.Rastogi Pub. https://www.ncbi.nlm.gov/pmc/articles/PMC3762664/#!po=12.1875 https://journal.lib.uoguelph.ca/index.php/surg/aticle/view/1239/1801 https://www.scribd.com/mobile/doc/22240581/xerophytes-plants-with-special-characteristics-such-thst-they-can-survive https://link.springer.com/chapter/10.1007/978-3-642-32653-0_2