Anthoceros
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.A. adscendens Lehmann & Lindenberg 1832A. agrestis Paton 1979A. alpinus Stephani 1923A. angustifolius Gottsche, Lindenberg & Nees 1846A. angustus Stephani 1916A. assamicus Kachroo 1954A. bharadwajii Udar & Asthana 1985A. buettneri Stephani 1916A. capricornii Cargill & Scott 1997A. caucasicus Stephani 1923A. cavernosus Stephani 1916 non Nees 1838A. chambensis Kashyap 1917A. chungii Khanna 1938A. crispatus Griffith 1849A. cristatus Stephani 1916A. dimorphus Sim 1926A. dissectus Montagne 1846A. erectus Kashyap 1915 non Stephani 1916A. expansus Villarreal & Cargill 2015A. ferdinandi-muelleri Stephani 1916A. fragilis Stephani 1916A. fusiformis Austin 1875A. gasongorii Gola 1914A. granulatus Gottsche 1863 non Colenso 1886A. harrisanus Parihar 1962A. helmsii Stephani 1893A. jamesonii Taylor ex Mitten 1855A. javanicoides Miller 1981A. jungermannioides Schweinitz 1821A. kajumas Proskauer 1951A. khandalensis Proskauer 1951A. koshii Khanna 1936A. lamellatus Stephani 1916A. laminiferus Stephani 1893A. macounii Howe 1898A. macrosporus Stephani 1916A. major Griffith 1849 non Micheli 1729 ex Schmidel 1766 non Smith 1806A. maritimus Stephani 1916bA. megasporus Meijer 1957A. muscoides Colenso 1884A. myriandroecius Stephani 1911A. natalensis Stephani 1913A. neesii Proskauer 1958A. niger Stephani 1916A. orizabensis Hässel 1990A. pandei Udar & Asthana 1985aA. patagonicus Hässel 1990A. peruvianus Stephani 1916A. pinnatus Stephani 1886A. punctatus von Linné 1753A. pusillus Colenso 1886b non Stephani 1916A. rosulans Hasegawa 1986A. sahaydrensis Sane 1942A. sambesianus Stephani 1916A. sampalocensis Proskauer 1948A. scariosus Austin 1869A. schroederi Stephani 1912A. serratus Stephani 1911bA. simulans Howe 1934A. spongiosus Stephani 1916A. stephanianus Beauverd ex Stephani 1924A. subtilis Stephani 1916A. telaganus Stephani 1916A. tristanianus Villarreal, Engel & Váňa 2013A. tuberculatus Lehmann & Lindenberg 1832A. venosus Lindenberg & Gottsche 1846 non Spruce 1885