Montana Field Guide

Taxonomists have often differentiated the aquatic species of Rhynchostegium (Family Brachytheciaceae) as the distinct genus, Platyhypnidium (Family Amblystegiaceae). The FNA (Volume 28) treatment includes these aquatic species in (the broad sense of) Rhynchostegium as they have been shown phylogenetically to have originated several times. Additionally, the American-Asian-Australian populations of Rhynchostegium ripariodes have different origins than the European-African populations. The widespread population in North America is regarded by FNA as R. aquaticum.

Plant: Mats. Dark-green becoming brown when old. Stems are 4-10 cm tall, usually with a few branches, but occasionally simple.

Leaf: Leaves imbricate to somewhat spreading, 1.4-2.4 x 0.8-2.0 mm, broadly ovate to suborbicular, usually concave, not plicate, and not decurrent. Leaves widest at about the middle. The apex is acute to broad and almost rounded or occasionally apiculate. Margins plane, distinctly serrate to the base or nearly so. Costa is variable, ½ or ¾ the length of leaf and usually ends with a spine; sometimes the costa reaches the apex and rarely it is forked.

Leaf Cells: Median cells long and narrow, 40-75 x 4-5 µm. Cells shorter at the base and apex. Alar cells are a little differentiated, often hyaline and sometimes somewhat inflated.

Aquatic, attached to stones in or at the edges of streams and springs with running water (Elliott 2016). Widespread, but never abundant in the Pacific Northwest.

Autoicous. Seta 1.0-1.5 cm long, smooth. Capsules shrunken under the mouth when dry and 1.6-2.0 mm long.