Abstract
Achlya fuegiana sp. nov., occurring on litter (floating dead leaves and twigs) in Laguna Verde stream, in Tierra del Fuego Province (Argentina) is described, illustrated and compared with similar species. The species produces principally papillate oogonia and androgynous antheridial branches. Immature oospheres, oogonial wall and oospores are distinctly yellowish. This Argentine species differs from other known ones with centric-subcentric oospores in having monoclinous, exiginous, and diclinous branches, a great number of secondary hyphae near the tips and non-functional antheridial branches. The oospores are centric-subcentric and 1–3(7) in number, and borne inside the oogonia.
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