Gametophyte Rhynchostegium are small to large mosses that form either loose tuft or extensive mats on the substrate, with irregular or regular branching. The younger plants are generally deep green or light green; aging plants could become whitish, brownish, or paler green. Stems are creeping and lack hyaloderm, with acute to acuminate pseudoparaphyllia. Stem leaves are
erectopatent or
erect. Branch leaves are similar in morphology to stem leaves but smaller and sometimes narrower. Leaves are commonly straightly to homomallously arranged; subimbricate, subcomplanate, or complanate arrangement are sometimes seen, especially in branch leaves. Leaf base, decurrent or not, varies from
ovate to ovate-cordate, occasionally
lanceolate, and the narrowing from gradual to abrupt, towards a short- or long-
acuminate apex, where sometimes a differentiated long acumen or apiculus is present. The leaves have a single costa that generally smoothly ends 35-75% up the leaf, and more often in branch leaves in an
abaxial spine. Leaf surfaces vary from flat to slightly concave and not to strongly longitudinally plicate, with little to some pores and linear laminal cells. Leaf margins are serrate to
serrulate. Axillary hairs constitute of 3-7 cells, with 1-3 upper cells. Alar cells are slightly enlarged, and either undifferentiated or quadrate to elongate-rectangular.
Sporophyte Rhynchostegium are
autoicous. Covered by a naked calyptra is a rostrate to long-rostrate operculum attached to a red-brown to brown, oblong-cylindric, weakly curved capsule, which is inclined or horizontal to a red-brown, smooth seta that has abruptly contracted perichaetial leaves at the base, with acumen straight to reflexed. An annulus separates the operculum. The peristome is xerochastic and perfect, which the red to orange-red exostomes have reduced trabeculae and cross-striolae at the base of the teeth; in rare cases the exostomes are narrow and yellow. The broadly or narrowly perforated endostomes and developed to vestigial cilia are supported by a low or high basal membrane. Spore diameters range between 9-16 μm. == Biochemistry ==