Reboulia: features, anatomy, morphology etc.

Reboulia

1. REBOULIA

2. SYSTEMATIC POSITION KINGDOM : PLANTAE DIVISION : MARCHANTIOPHYTA CLASS : MARCHANTIOPSIDA ORDER : MARCHANTIALES FAMILY : AYTONIACEAE GENUS : REBOULIA SPECIES : R.hemisphaerica

3. OCCURREANCE AND DISTRIBUTION Plants are found in dense patches of overlapping thalli which are green with purple margins . This is a perennial liverworts consisting of a low mat of dichotomously branched thalli. Reboulia has one species, R. Hemisphaerica earlier very widely distributed in himalayas, south india and central india, but is now becoming depleted in these areas. It is widely distributed throughout the world ,occurring on all continents except antartica. The native purple-fringed liverwort(R.hemisphearica)is widely scattered throughout Illinois,where it is uncommon overall. In Illinois ,habitats include the rock walls of cave entrance, sandstone walls of rocky hollows,ledges and crevices along north facing sandstone and limestone cliffs,moist shaded areas of sandstone outcrops in woodlands,shaded muddy banks of creeks, rocky wooded hillsides,etc…. Reboulia comprises of only a single polymorphic species, Reboulia hemisphaerica,

4. EXTERNAL MORPHOLOGY Plant body is gametophyte,It is pale green, dichotomously branched thallus with slightly undulate margins and a distinct midrib. An individual thallus has a relatively flat ribbon- like appearance, becoming slightly wider towards it’s growing tip. ;the latter is often deeply notched. Thallus differentiate into dorsal and ventral region. The upper surface of the thallus is light green, yellowish green and relatively smooth ,indistinct white air pores are visible near upper surface. The lower surface of the thallus is primarily purple. Midrib is thick Rhizoids and scales are arise from the ventral surface. The thallus bears smooth and pegged rhizoids and 2-ranked ventral scales without appendages . Scales are one cell thick ,purplish and are arranged in two rows one on each side of midribs. The body of thallus is differentiated into a lower colorless region of compact elongated cells and an upper region of loose chlorophyllose tissue containing large air chamber.

5. Air chambers are abundantly formed and developed by centripetal splittings and are arranged in several rows. Pores are somewhat elevated with 3 to 5 (rarely upto 8)concentric rings of 6 to 8 cells each No chlorophyllose filaments are formed. The formation of a definite oil cells from an ordinary vegetative cell is a common features of the genus. No gemmae are produced.

6. T.S OF THALLUS Dorsal epidermal layer containing cells which are 4- 6 angled and pores(a little elevated). Dorsal air chamber present Parenchymatous cell zone Ventral surface layer with purple scales in one on each side of the midrib and rhizoids

7. REPRODUCTION Reproduction by means of vegetative and sexual methods. Vegetative reproduction by progressive death and decay of the thallus Specialized asexual reproduction is absent. Sexual reproduction is oogamous type. Gametes are produced in the sex organs(antheridia and archegonia) It may be dioecious or monoecious(autocious). Antheridia(male sex organ) and archegonia(female sex organ)

8. ARCHEGONIUM The archegonia are borne on receptacles which arise as dome like areas at the growing point of thallus . Archegonial receptacles become lifted up on a stalk only after sporophyte are approaching maturity. Their stalk remain surrounded at the base and the apex by narrow scales with a singles rhizoid furrow. Receptacles are conical or hemispherical divided to the middle into 4 to 9 obtuse lobes. The species(R.hemisphaerica) is presumably named after the hemispherical shape of its female reproductive organ(archegonium). Air chambers with compound pores are found on them. Involucre arise on the underside of the lobes from the margins. These are bivalve. Each involucre encloses a single sporogonium .Perianth is not found.

9. Archegonium has a swollen portion ,the venter and elongated part,the neck . Mature archegonium contains 18- 20 neck canal cells,but only 4 are present at the time of division of the ventral cell. The neck in all cases shows 6 cells in cross section , as among other marchantiales, in reboulia the neck canal cell is 4.

10. ANTHERIDIUM Antheridia occur in sessile lunate receptacles which are sometimes irregular in outline and broken up into several pieces. Receptacles is cushion- shaped and slightly raised above the general level of the thallus. The male receptacles are usually located only 1- 10 mm behind each female receptacle on the thallus. The number of antheridia in a receptacles varies from 16 to 100. Usually 2 or rarely 3 groups of antheridia are produced successively on the thallus before the appearance of the archegonial receptacle.

11. Water is essential for fertilization. Anthrozoids from antheridia are liberated to the surrounding water. During fertilization the ventre canal cells and neck canal cells of archegonia disintegrate. The sperm or the anthrozoids enters through the neck canal cell and reaches the egg cell. Undergoes fertilization, results in diploid zygote. The first cell of sporophytic generation

12. SPOROGONIUM Sporogonium consists of relatively large foot ,short stalk(seta) and a globulose capsule. The wall of the capsule is unistratose.Capsule dehisces irregularly at the apex. A single capsule of R.hemisphaerica produces around 3,000 spores ,which are viable for atleast five month. Spores are brown,spherical,reticulate- lamellate with broad wing.Unicellular Elaters have two to three spiral thickenings and are coiled,long and rarely branched.

13. After fertilization male receptacle become somewhat shrivelled,while female receptacle become elevated on a stalk (seta) about 1-3 cm high. Depending on the environmental condition and maturity ,the stalk can be white,light green,yellow etc.. The dome shaped head of the female receptacle (carpocepalum)become more lobed as it matures.These lobes partially separated from each other by downward- sloping indentations. 4-7 ovoid spore cases are present the undersise of female receptacles ,which is having white memberanous covering. Mature spore cases become dark purple or black in colour,where as the immature ones are light green or yellowish green.

14. LIFE CYCLE

15. THANK YOU