T: Juncus acutus L., fide N.L.Britton & S.Brown, Ill. Fl. N. U.S., ed. 2, 1: 465 (1913).
Perennial or rarely annual herbs, caespitose to rhizomatous, seldom mat-forming, totally glabrous, smooth or papillose. Stem erect, procumbent or ascending, terete to compressed. The most basal leaves usually lacking blade or blade much reduced (cataphylls); fully developed leaves alternate, basal and/or cauline, flat (flat side facing stem), not septate, or flat with raised margins and enlarged cells on adaxial surface, or terete either solid or hollow and with or without septa, or laterally flattened (arranged perpendicular to stem) and imperfectly septate; sheaths open, rarely closed and later split, often with distinct auricles at the junction to blade. Bracts leaf-like or reduced. Inflorescence compound, often decompound, cymose or racemose, often anthelate, sometimes congested, or flowers borne singly in drepania with or without a pair of bracteoles below each flower. Flowers bisexual, rarely unisexual; usually trimerous, rarely dimerous. Tepals usually 6, entire, equal or unequal, persistent, green, stramineous, castaneous to blackish, smooth or scabrid, narrowly ovoid to linear lanceolate. Stamens (2–) 3–6, exserted or not so; filaments filiform or flattened; anthers linear to oblong; connective indistinct or slightly apiculate. Ovary sessile; style almost absent to very long; stigmas (2–) 3, filiform, twining, papillose, of variable length and colour. Capsule unilocular, triseptate or perfectly trilocular; seeds many, usually ellipsoid to ovoid; outer seed-coat tight and hyaline to loose, scarious, smooth to reticulate, forming one apical and one basal whitish appendages or not so; inner seed-coat brown, castaneous or yellowish, ±smooth to reticulate. x = 10 (many additional secondary basic numbers exist, ranging from x = 9 to x = 25 at least, the role of agmatoploidy being unknown).