Riccia fluitans
This species is recognized by the broadly, conspicuous air chambers in thallus cross section; spores 50-70 µm diameter, and each with small reticulate areolate on the upper hemisphere, the lower hemisphere with larger areolations and with incompletely secondary partitions.
Thalli yellowish-green; branching irregularly pinnate branched; rhizoids mostly smooth with some of tuberculae; air-pores simple, composed of 4-ringed cells; thalli cross section 6-10 cells thick, with 1-3 layers of reticulate air-chambers; epidermal cells quadrate to hexagonal, thin-walled, smooth; ?Autoicous. Male inflorescences not seen; female inflorescences embedded on the ventral side of thallus midrib; sporophytes cleistocarpous; spores with triradiate ridges, 50-70 µm diameter, and each with small reticulate areolae in the upper hemisphere, lower hemisphere with larger areolations with incomplete secondary partitions.
Widely distributed in North America, Europe, Asia, Africa, and Thailand (Conard, 1956; Meijer, 1958; Wigginton, 2002; Lai et al., 2008, Gradstein, 2011). Specimens examined—Printarakul 19, 113, 3831, 5382, 5393, 5865, 5998 (all CMU).
On soil in primary, evergreen seasonal, hardwood forest, granite bedrock, Pu Ping Palace, c. 1,400 m elevation; on soil in mixed evergreen+deciduous, seasonal, hardwood forest, granite bedrock, Montahtahn Falls, c. 889 m elevation; on soil in deciduous-dipterocarp-oak, seasonal hardwood forest, granite bedrock, Daht Mawk Falls, c. 544 m elevation.