Selaginella ppt
- 1. Selaginella NARESH KUMAR PRASAD B.SC. (H) BOTANY SEMESTER -2
- 2. SYSTEMIC POSITION Division : pteridophyta Class: lucopsida Order: Selaginellales Family: Selaginellaceae Genus: Selaginella
- 3. Distribution and habitat It has world wide distribution Abundant in tropics and grows in ground and shedy places.
- 4. morphology The plant body is sporophyte and is differentiated into : 1.Root 2.Stem 3.Leaves
- 5. Root The root of young sporophyte is of primary root while others are adventitious. The adventitious roots are at the tips of rhizophore.
- 6. Stem Stem is green, dorsiventral and prostrate with short erect branches. The branches are arranged dichotomously. The shoot apex consists of a single apical cell in most cases.
- 7. Rhizophore In some species , leafless and colorless branches arise from the prostrate stem near point of branching. These grow downwards and have group of adventitious roots They are called as rhizophores Some scientist consider them branches and some consider them as roots and still other consider it as an organ for protection or other function. But recently they are known as adventitious roots that have dichotomous branches at tip.
- 8. Leaves Microphylls are present. ( leaves are small and single veined. They are of 2 types 1. Isophyllous 2. Anisophyllous. The anisophyllous leaves are in pairs. They may be Small: these are inserted on the dorsal side of stem Larger: these leaves are inserted on the ventral side of stem
- 9. Ligules Ligule: there is small outgrowth on adaxial side ( upper side) of the leaf near base. It is vestigial organ and provide water .
- 10. Anatomy Stem anatomy Leaf anatomy Root anatomy
- 11. Stem anatomy Epidermis : thick epidermis , thin walled, rectangular cells, covered with cuticle cortex : many layered , outer 2-4 are thick walled called as hypodermis endodermis :the cortex and central tissue is connected by radially elongated cells called trabeculae
- 12. Leaf anatomy The upper and lower epidermis are present They are one celled thick and contain chloroplast Stomata are present on upper and lower epidermis ( but majority have in lower side) Below the epidermis there is mesophyll tissue having thin walled parenchyma cells, these contain chloroplast and have small and large air spaces Vascular tissue is present in center
- 13. Ligule
- 14. Strobilus The strobilus is the spore-bearing structure, with both male and female spores being produced. The male spores are contained within the sac at lower right. The much larger female spores are in the sac at lower left.
- 15. Asexual reproduction These are hetrosporous 1. Microspore of smaller size produced in microsporangia 2. Macrospores of larger size produced in macrosporangia .
- 16. Structure of sporangia Microsporangia : they are small, stalked, oval and varying in shapes, Mega sporangia : they are stalked and 4 lobes, larger in size and present at base of strobilus , spores are of larger size. 1. Both consist of 2 layered sporangial wall surrounding the tapetum and sporogenous tissue. 2. Tapetum is developed from innermost layer of sporangial wall. 3. Both differ in their size, location, and number of spores.
- 17. Sexual reproduction ( gametophyte ) Microspores and macrospores develop into male and female gametophyte Germination is precocoious ( within the walls of sporangia) Male gametophyte is released at 13 celled stage while female gametophyte comes at various stages , depending upon the species.
- 18. Microspore The microspores are very minute in size. The spore wall is two- layered. The outer exine is very thick . The inner inline (endospore) is thin and delicate. The spore consists of reserve food material in the form of oil globules and nitrogenous material.
- 19. Megaspores The megaspores are much bigger in size than the microspores . The wall of the megaspore is very thick and consists of a exine, a middle mesospore and a thin intine.
- 20. Life cycle Life cycle in selaginella is characterized by alternation of generation. Both spore producing and gamete producing generation are independent.
- 21. References Vashistha, P.C., Sinha, A.K., Kumar, A. (2010). Pteridophyta. S. Chand. Delhi, India. Images- www.shutterstock.com
- 22. Thank you