Bryophytes: alternation of generation, morphology, anatomy and reproductive characters of Riccia

Bryophytes: alternation of generation, morphology, anatomy and reproductive characters of Riccia

1. Bryophytes – Alternation of generation, Morphological, anatomical and reproductive characters of Riccia Sankrita Gaonkar Assistant Professor in Botany [email protected]

2. Contents Alternation of generation Riccia – morphological, anatomical and reproductive characters References

3. Alternation of generation Gametophyte: Sexual generation – haploid phase (n) Bears reproductive organs – antherozoids and eggs Gamete fusion – zygote formation – develops into sporophyte Sporophyte: Diploid phase (2n) Produce spores – germinate to form gametophyte Formation of spores – meiotic division – produce haploid spores Involvement of fertilization (syngamy) and meiosis (reduction division) in gametophytic and sporophytic phases Alternation in life cycle in two distinct individuals with different function – Diplohaplontic life cycle Morphologically different generations – Heteromorphic type of alternation of generation Gametophyte  sporophyte  gametophyte

4. Riccia Classification: Class: Hepaticopsida Order: Marchantiales Family: Ricciaceae Genus: Riccia

5. Morphology Gametophyte: Plant body – thallus Small, green, flat and fleshy Grows prostrate and branches dichotomously – Rosette form Thallus branches called as thallus lobes Lobe thickest in middle (midrib) and thins towards margins Upper surface of lobe – median groove or furrow – dorsal groove Rhizoids – simple, unicellular – smooth-walled and tuberculate

6. Anatomy 2 regions: i ) photosynthetic region ii) storage region Photosynthetic region: Loose, green tissue – parenchymatous cell with chloroplast - vertical rows – function as pseudomesophyll Narrow, deep vertical slits between columns of green cells – air canals or air channels Uppermost, pear-shaped cell – pseudoepidermis – have air pores

7. Storage region: Ventral portion of thallus Closely packed parenchymatous cells without intercellular spaces Contain starch but no chloroplast Serve for water and food storage Lowermost cells – lower epidermis – rhizoids arise

8. Reproduction: Vegetative and sexual reproduction Vegetative reproduction: i ) Fragmentation Depends on ageing of vegetative cells Older cells die – young lobes separate and grow into new thallus ii) Adventitious branches Arise from ventral surface of thallus in midrib region iii) Persistence apices Occurs in species growing in regions with long dry periods iv) Tuber formation Apices of thallus lobes become thickened

9. Sexual reproduction Sex organs develop on thallus lobes Lie in dorsal furrow or groove – sunk deeply Younger ones at tip and older ones away Antheridia and archegonia - same thallus ( Monoecious ), different thalli ( Dioecious )

10. Structure of sex organs A) Antheridium Stands in deep pit – antheridial chamber – attached to multicellular stalk Narrow pore at tip – ostiole Outer sterile jacket layer – antheridial wall – protection Mass of cells - androcyte mother cells – divides to form 2 sperm cells – spermatids or androcytes Sperm – minute, slender, curved – pair of whiplash flagella Dehiscence – presence of moisture Water enters ostiole and antheridial chamber

11. B) Archegonium Flask-shaped 2 parts – i ) basal swollen portion – venter , ii) long, slender – neck Vertical row of 4 cells – neck canal cells – surrounded by sterile protective jacket ( neck cells ) Neck cells – six rows Neck tip – 4 large cap or cover cells Venter jacket – venter wall – enclose venter cavity having 2 cells ( egg cell and ventral canal cell ) Ventral canal cell – function as plug holding egg cell Dehiscence – at maturity, neck cells and ventral canal cells degenerate – form mucilage when hydrated

12. Fertilization Takes place in presence of water Antheridium burst and release sperms Simultaneously, neck canal cells degenerate – form mucilage Cover cells separate from each other Sperms enter through archegonial neck One sperm penetrate egg Fusion of sperm and egg nucleus takes place

13. Sporophyte ( sporogonium ): Simplest among liverworts Lack foot and seta Have a spore sac – single layered wall Spore mother cells in spore sac 2 layered calyptra Mature spores lie free in sac after break down of sporogonium wall and inner calyptra layer Elaters absent

14. References Vashishta BR. 2010. Botany for degree students: Bryophytes. S. Chand & company ltd. Pandey B.P. (2009). Botany for degree students: B.Sc. First Year. S. Chand & Company Ltd. New Delhi.