Guide to Liverworts of Oregon: Riccia frostii Aust.
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Riccia 1b terrestrial > Riccia 2b marginal projections lacking > Riccia 5a surface spongiose > Riccia 6b surface obscurely lacunose or smooth > 6.1a surface distinctly lacunose > Riccia frostii
Synonym: None.
Special Status: None, but probably should have.
Recognition: Small thalli with a dull sheen caused by the spongiose surface barely visible to the naked eye. It is not as well developed as in R. cavernosa where the spongiosity is prominent. Dioicous. Vermiculate ornamentation on distal surface of spore.
Distribution: Grows on bare soil; an annual ephemeral. Distibution in Oregon is not clear; definitely known from California and to be expected in Oregon.
Comments: As with most species of Riccia, this is to be looked for in the brief period when plants develop on damp soil that dries out later in the season.
A recent report of this from British Columbia has nice pictures. SEM images of spores below were prepared by W.T. Doyle, used by permission.
West end of Rooster Rock State Park, Multnomah Co., Oregon. N. Otting field photo, 16 October 2017. Note both red (male) and green (female) phenotype. Also: Equisetum gametophyte (E. hyemale?) with young sporophytes.
Distal aspect. San Gabriel Mts., Los Angeles Co., California. Wheeler 6344 (UC), W. Doyle SEM.
Proximal aspect. San Gabriel Mts., Los Angeles Co., California. Wheeler 6344 (UC), W. Doyle SEM.
Side view. San Gabriel Mts., Los Angeles Co., California. Wheeler 6344 (UC), W. Doyle SEM.