Selaginella for BSC Botany students.pptx

This presentation explains the morphology, anatomy, and reproduction of Selaginella, a unique pteridophyte known for its heterospory and resurrection ability. It covers structural features, internal organization, and reproductive adaptations that link lower and higher vascular plants, highlighting its evolutionary significance.

1. Pteridophytes - Selaginella

2. CONTENTS Introduction Morphology : Leaves, Ligules, Rhizophore,Roots Anatomy : Stem Reproduction: Vegetative & Asexual Resurrection, Economic Importance

3. Introduction Selaginella is the only living genus of the order Selaginellales & is commonly known as ‘spike moss’ or ‘small club moss’. It is a large genus comprising of about 700 species distributed all over the world. Abundantly it is found in tropical rain forests. Most of the species prefer moist and shady places to grow but few are also found growing in xerophytic conditions i.e. on dry sandy soil or rocks e.g : S. lepidophylla , S. rupestris etc. A very few species are epiphyte e.g : S. oregena . It is found growing on tree trunks.

4. Based on the structure of plant body Selaginella has been invited into 2 sub genera namely: Homeophyllum: The plants belonging to this sub genus have erect & dichotomously branches stem. Leaves are of same size and are spirally arranged. This genus includes 50 species. Ex: S. rupestris, S. selaginoides, etc Heterophyllum: These are usually prostrate & dorsiventral stem with erect branches. Most of the species belong to this sub genus. Foliage leaves are arranged in 4 vertical rows on the stem. The 2 dorsal rows have small leaves and the 2 lateral rows have large leaves Ex: S. kraussiana, S. Lepidophylla, etc

5. Morphology Stem : Stem is usually erect in Homeophyllum , sub erect in the Heterophyllum. The stem always shows dichotomous branching. Rhizophore : These are long cylindrical, unbranched prop - like colourless & leafless branches of the stem found in some species of selaginella. Generally they arise from the lower side of the stem at the point of dichotomy which grows vertically downwards. Under certain conditions it may develop into some typical leafy shoots.

6. Root : Primary roots are ephemerals, so adult plant has only adventitious roots. In creeping species with dorsiventral stem roots arise from the point of dichotomy. In few species it may arise from the knot like swelling present at the basal portion of stem or from the apices of the rhizophore.

7. Leaves: Stem is covered by 4 rows of dimorphic leaves in Heterophyllum, where as in Homeophyllum all leaves are alike ,which are spirally arranged. The leaves are sessile, simple, shape varies from ovate to lanceolate. Ligule: Vegetative leaves & sporophylls are ligulate i.e, each leaf has a small tongue like/ lobed membranous flap on the upper surface near the base. It has 3 portions namely glossopodium, body & terminal lamella. Glossopodium is enlarged , hemispherical basal portion. Body is the cylindrical middle portion. Terminal lamella is the pointed tip of the ligule.

8. Rhizophore : The T.S of rhizophore reveals the following details: Epidermis, single layer of outer outermost parenchymatous consisting of cutinised cells. Cortex many layered outer fewer thick walled sclerenchymatous – hypodermis, followed by inner thin walled parenchymatous cortex. Endodermis is single layered thin walled cells. Pericycle is single layered which forms the boundary of the stele. Stele is protostelic type that is Xylem is at the centre surrounded by phloem in exarch condition (metaxylem towards the centre & protoxylem towards the periphery) Anatomy

9. Stem – The T.S of the stem shows the following details: Epidermis : It is the outermost covering layer, which is made up of a single cell in thickness. The cells of the epidermis are without hairs and stomata. The epidermis is surrounded on all sides by a thick coating of cuticle. Cortex : It is a well-defined zone of cells below the epidermis. It may or may not be differentiated into inner and outer cortex. The cortex may be composed of thin-walled parenchyma cells or thick-walled sclerenchyma cells or both. Stele : It is the central part of the stem, consisting of xylem, phloem and pericycle. The stele may be protostelic (xylem in the centre and phloem around it) or siphonostelic (xylem and phloem separated by a pith). The stele remains suspended in the centre by radially elongated tubular structures called trabeculae, which are formed by the endodermal cells with casparian strips. Between the trabeculae, there are large air spaces. The number of steles may vary from one (monostelic) to many (polystelic).

10. The xylem is usually exarch (protoxylem towards the periphery) and may have one (monarch), two (diarch) or more (polyarch) poles. The xylem is composed of tracheids only, vessels are absent. The phloem surrounds the xylem and consists of sieve cells and phloem parenchyma. Companion cells are absent in phloem. The pericycle is a single layer of cells around the stele.

11. Leaf : leaves are one cell thick, which possesses upper and lower epidermis. Stomata are present only on the lower epidermis along the mid rib. In few species both upper & lower epidermis bears stomata. Below the epidermis mesophyll tissue is present. Each leaf has single vascular bundle which is comprised of xylem surrounded by phloem & single layer of bundle sheath enclosing the vascular bundle.

12. Reproduction Selaginella reproduces Vegetatively & also by Asexual Reproduction Vegetative reproduction : Fragmentation: During favourable conditions prostrate branches produce roots. These branches break away from the parent plant and grow to new plants. Tubers: These appear towards the end of the growing season. The tubers maybe aerial, developing at the apical and of the aerial branches under favourable conditions tubers germinate into a new plant. Dormant buds: Aerial branches of some species bear some resting or dormant buds which germinate to new plants during favourable conditions.

13. Asexual reproduction in Selaginella: This is a sporophytic plant which is heterosporous. It produces two types of spores they are microspores and megaspores. These spores are produced in microsporangia and megasporangia respectively which in turn are produced on fertile leaves known as mega sporophylls and microsporophylls respectively. Usually both these structures are grouped together to form a compact structure known as strobilus, which is a terminal structure. Strobilus it is a reproductive structure formed by the aggregation of ligulate sporophylls at the apex of the branches of stem in some species the growth of the stem continues beyond the strobilus and such condition is called selago condition that is fertile part is alternated by vegetative parts

14. The L.S of strobilus shows that it is a very simple structure it consists of a central axis covered with spirally and densely arranged ligulate sporophylls. Each sporophyll adaxially bears a single stalked sporangium in its axis. Selaginella produces two types of spores that is megaspores and microspores in between the sporophylls and sporangium there is a small membranous structure known as ligule. The sporophylls are similar to vegetative leaves. The microsporangium produces numerous microspores whereas megasporangium produces usually 4 megaspores L.S of Strobilus

15. Fertilization The process of fertilization occurs when megaspores with female gametophytes fall on moist soil & microspore containing male gametophyte fall close to the female gametophyte & a film of water is present when the antherozoids are liberated. They swim in water and get attracted towards the chemical substance secreted by the archegonial neck cells at the time of maturity. The neck canal cell, the venter canal cells & venter cells degenerates, then antherozoids enter through the neck cell and fuses with the egg cell, thus forming diploid zygote.

16. The zygote is the 1 st cell of the sporophytic generation. It secretes a protective wall & grows into an embryo which later develops into a sporophyte of selaginella. The embryo development is endoscopic.

17. Life Cycle of Selaginella

18. Resurrection This is the ability of a plant to survive in dehydration to an air dried state for months, losing most of their cellular water, & quickly resumes to normal physiological activities after rehydration After Resurrection Before Resurrection

19. Economic Importance Medicinal value : Some species are used in traditional Chinese medicine for various ailments, such as cough, asthma, rheumatism, bleeding, etc.  For example, Selaginella tamariscina is known as “blood flower” and is used to stop bleeding and promote blood circulation . Ornamental value : Some species are cultivated as ornamentals for their attractive foliage and ability to revive after drying. For example, Selaginella kraussiana is a popular plant for terrariums and hanging baskets Ecological value : Some species are important components of the ecosystem, providing food and shelter for other organisms, stabilizing the soil, and influencing the microclimate. For example, Selaginella bryopteris is a lithophyte with remarkable resurrection capabilities that can grow on bare rocks and help in soil formation.

20. References https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8558194/#:~:text=Resurrection%20plants%20are%20a%20unique,activities%20after%20rehydration%20%5B1%5D https://youtube.com/shorts/-rCTimWAu7U?feature=share

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