Genus of hornworts
Anthoceros is a genus of hornworts in the family Anthocerotaceae. It is distributed globally. Species of "Anthoceros" are characterized by having a small to medium-sized, green thallus that is more or less lobed along the margins.
Etymology.
The name "Anthoceros" means 'flower horn', referring to the characteristic horn-shaped sporophytes that all hornworts produce.
Description.
The spores are dark gray, dark brown or black. This distinguishes it from the related genus "Phaeoceros", which produces yellow spores. The thallus lacks air chambers and scales, and has no well defined mid rib. It has unicellular smooth rhizoids in the ventral region. It is irregularly lobed, and exhibits rare dichotomous branching. The thallus has little to no tissue differentiation, being composed of thin, compactly arranged uniform parenchymatous cells.
"Anthoceros" species are host to species of "Nostoc", a symbiotic relationship in which "Nostoc" provides nitrogen to its host through cells known as heterocysts, and which are able to carry out photosynthesis. The "Nostoc" colonies are present on the lower ventral surface. They often grow in slime pores, mucilaginous groups of decomposed cells within the plant which open outward through a pore guarded by 2 cells. "Nostoc" colonies are visible as blue-green patches on the plant body.
The plants grow in moist clay soils on hills, in ditches, and in damp hollows among rocks.
Reproduction.
"Anthoceros" species exhibit many forms of asexual reproduction. Besides fragmentation, a nearly ubiquitous form, these hornworts exhibit tubers, persistent apices, and apospory. Tubers and persistent apices can remain dormant and survive harsh conditions to form new thalli. Apospory, a form of apomixis, involves the formation of diploid gametophyte spores directly from the tissue of the plant's sporophyte.
Species.
List of species.
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References.
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