Describe the salient features of Anthoceros. Mention the biological significance of the sporophyte of the same.

(i) Thalli grow in dense patches on the moist soil and wet rocks in all hilly places including Himalayas.

(ii) Dorsiventral greenish thallus without any definite symmetry may be prostrate, ascending or erect; margin smooth or sinuate.

(iii) The dorsal surface may be smooth, rough or velvety and without midrib while the ventral one with slime pore and smooth walled rhizoids.

(iv) The growth is due to a pyramidal apical cell or marginal meristem.

(v) There is no internal zonation. All the chlorophyllous cells have a single chloroplast each. Each chloroplast has either a large pyrenoid or 200-300 tiny pyrenoid bodies. There are a few mucilage cavities containing the colonies of an endophytic Nostoc.

(vi) The thallus propagates vegetatively by means of tuber, gemma, persistent growing apices and isolation of younger branches or lobes.

(vii) The sexuality is oogamous. The thallus may be dioecious or monoecious-protandrous.

(viii) Dorsal surface of male thallus bears androecial spots in uniseriate acropetal order, each spot being the locus of an antheridial chamber.

(ix) The roof of antheridial chamber and group of 1-25 antheridia develop from the same superficial cell, yet the ontogeny of antheridium is endogenous.

(x) Secondary antheridia develop either by budding of the stalk cell or the basal cell seated below the stalk (of primary antheridia) having 4 vertical tiers of cells.

(xi) The antheridial spot on maturity develops a distinct slit. Antheridia dehisce apically in contact with water.

(xii) The body of biflagellate antherozoid may either be linear or with a broader head. The length of flagella is equal to the body. Blepharoplast may or may not appear.

(xiii) Sessile sunken archegonium is devoid of its own jacket. The axial row in the neck contains 4-6 NCC.

A rosette of 4 cover cells, being barely projected of the thallus, is encircled by a funnel-shaped mound of mucilage.

(xiv) Non-papillate structure of archegonial initial and absence of transverse division are attributed to the sunken nature of archegonium.

(xv) The 1st and 2nd divisions of zygote are normally vertical and transverse respectively. Both the transverse tiers at quadrant stage may either be equal or the epibasal tier bigger. The derivatives of epibasal tier form capsule and intercalary meristem.

(xvi) Massive bulbous foot sunken in the gametophytic tissue bears palisade layer-like peripheral cells being of haustorial nature.

(xvii) Presence of l-more massive cylindrical sporogonia (length = 2∙15 cm) in erect posture on the thallus justifies the term hornwort.

(xviii) Calyptra absent. Involucre of gametophytic origin forms a collar-like sheath at the capsular base.

(xix) Continuous addition of new cells by intercalary meristem makes the sporogonium indeterminate.

(xx) True stomate-bearing epidermis and chlorophyllous wall layers of jacket make the sporophyte nutritionally self-sufficient.

(xxi) The squarish columella with 4 vertical tiers of 4 cells each extends up from the meristematic zone. It transports water and provides mechanical strength.

(xxii) Columella and archesporium originate from the endothecium and amphithecium respectively.

(xxiii) Tissue differentiation, sporogenesis and spore dispersal from base upwards are progressive continuous process.

(xxiv) The capsular dehiscence is bivalvular from tip downward through distinct dehiscent lines as per hygroscopic movement of jacket and pseudoelaters, the latter help in spore dispersal.

(xxv) Tetrahedral meiospore germinates to produce a germinal tube. The tip of this tube is utilized for the formation of multicellular thallus. As the growth proceeds there develop rhizoids and mucilage slits, the latter pave way for the entry of Nostoc,

Anthoceros occupies a valuable place as regards to its biological significance. On one hand it has most simplified gametophyte thallus while on the other a highly elaborated and advanced sporophyte is found. Its Or sporophyte shows following evolutionary tendencies in the line of biological evolution process.

(a) Physiological independence : The sporogonium of Anthoceros has complex photosynthetic system with functional stomata which evidently suggests the beginning of the physiological independence of it. It has been noted that in some cases of A. fusiformis, growing near water supply, the a sporophyte established direct contact with the soil and became practically independent from the gametophyte. These abnormal sporophytes exhibited the complete suppression of sporogenous tissue in younger part but in all cases, columella was very well developed. The amount of chlorophyllose cells also increased. Such a sporophyte, therefore, resembles with the primitive pteridophytes.

(b) Continuous intercalary growth: The presence of intercalary meristematic zone carrying out long and continuous growth of the sporophyte suggests the beginning of such characters in sporophyte.

(c) Conducting region: The presence of well developed columella (a central sterile portion) developed from the central endothecium suggests the beginning of the formation of conducting region.

(d) Increased amount of sterile tissue: A major portion of Anthoceros sporogonium consists of sterile tissue such as foot, capsule wall, columella and pseudoelaters. The increased amount of sterile tissue, therefore, suggests the beginning information of sporophytic plant body as in higher plants.

(e) Outward shifting of sporogenous tissue : In Anthoceros, the entire endothecium is converted into sterile columella while in members of Hepaticae, endothecium gives rise to sporogenous cells. In former, the spores are formed from amphithecium which represent the initial stage of formation of superficial sporangia.

(f) Reduction in sporogenous tissue : Reduction in amount and percentage of sporogenous tissue in a sporogonium is considered as an advanced character which is clearly evident from higher plants. Thus, reduction in the sporogenous tissue in Anthoceros, suggests the initial stage to produce limited number of spores.

(g) Tendency towards formation of sporangia : The alternate arrangement the spore mother cells and the sterile cells in the sporogonium suggests the beginning of the formation of sporangia.

(h) Indeterminate ripening of spores: All different stages of ripening of spores are found in a sporogonium of Anthoceros. The upper part of the capsule has well developed spores while the lower part has different stages of their development. This condition suggests the beginning of indeterminate ripening of spores in a sporophyte.

The earliest known vascular plant fossils (members of Rhyniaceae) from the Devonian rock of Scotland show certain remarkable resemblances with this group. The tips of some branches of Rhynia produce spores and sections of these sporangia show the presence of columella overarched by spores much the same as in Anthocerotopsida. These primitive plants accept Anthocerotopsida as their ancestral place of origin. Mehra (1957) stated that both Anthocerotopsida and Psilopsida arose from the common Anthorhyniaceae stock.

Follow on Facebook page – Click Here

Google News join in – Click Here

Read More Asia News – Click Here

Read More Sports News – Click Here

Read More Crypto News – Click Here