Coleanthus subtilis is a small-growing, clump-forming
annual grass that often grows on the ground. The
culms are thin, prostrate, or ascending, have two to three nodes, and a little groove. They grow to a length of 30 to 80 mm. The leaf sheaths are glabrous and closed in the lower half, especially the uppermost leaf sheath, which is strongly inflated. The ligules form a membranous fringe and scale between 0.5 and 0.8 mm. The glabrous
leaf blades measure 10 to 20 mm in length and 1 to 2 mm in width. They are weakly grooved, folded, and often shaped like a sickle. A
panicle can vary in size from 10 to 30 mm. It is composed of several more or less dense groups of spikes arranged in tufts. The
spikelets are uniflorous and grow 0.8 to 1.2 mm long. They stay on the panicle even after the ripening stage. The
glumes are missing. The tender-skinned lemmas are single-nerved and grow 0.8 to 1.2 mm in length. The remaining nerves are hairless, except for the median nerve, which is short and protruding hairy. They have an oval lower portion, an extended top portion, and a narrowly rounded or awn-pointed at the upper end. The two-nerved, glabrous, and tender-skinned bracteoles reach 0.4 to 0.6 mm long. They have wide, depressed sides and are four-pointed at the top. The two nerves each run out in a short tip. It develops into a pair of
stamens. The filaments are attached to the base of the
anthers, which have a length of approximately 0.3 mm. The
stigmas of the
ovaries are filiform and protrude from the flowers at the upper end. The
fruits lengthen from 0.6 to 0.8 mm. They are wrinkly, stick out between the top and the front husk, and fall off without external action.
Coleanthus subtilis typically blossoms from June through September, with very few occurrences in early May or late November. It is
diploid, with a
chromosome number of 2n = 14. == Distribution ==