Monographs Details: Riccia atromarginata Levier
Authority: Bischler, Hélène, et al. 2005. Marchantiidae. Fl. Neotrop. Monogr. 97: 1--262. (Published by NYBG Press)
Description:Species Description - Thalli in partial rosettes or in crowded mats; lobes 2-3 times forked, 3-6 mm long, 1-1.8 mm wide, rounded apically, margins obtuse; dorsal side bright green or bluish green, sometimes with violaceous spots, margins dark violet; flanks black-violet, completely inflexed when dry. Median groove shallow, often wide. Epidermal cells disintegrating except in groove, rounded or pyriform. Papillae numerous, smooth, hyaline, fingerlike, rounded apically, 60-210 µm long, always present on margins, often on flanks, and on dorsal side everywhere or near apex of lobes only. Ventral scales small, violet, margins entire. Cross section of lobes 0.6-0.7 mm high, as wide as high near apex of lobes, 1.5 times as wide as high below; dorsal edge rounded laterally; flanks erect, rounded apically. Dioecious. Archegonial necks protruding, dark violet. Spores tetrahedral, (75-)80-122 µm diam., dark red-brown or nearly black, wingless; distal face with 12-18 areoles of irregular shape across diam., with thick, nearly black ridges and large, black, sometimes anastomosed tubercles on corners; proximal face with similar ornamentation, triradiate scar weak. Gametophytic chromosome number n = 8 or 16.

Discussion:The Mexican collection belongs to var. atromarginata. The species can be distinguished from the other neotropical Riccia species by its fingerlike papillae, 60-210 µm long. Number, size, and distribution of papillae vary. The species is closely related to R. violacea and R. iodocheila, from which it differs by its numerous, long and smooth papillae.

Schuster (1992b) treated R. iodocheila as a subsp. of R. atromarginata and R. violacea as a synonym of subsp. atromarginata. In our opinion, Riccia atromarginata, R. iodocheila, and R. violacea are 3 distinct species.
Distribution:Nuevo León Mexico North America|