Juncus subg. Ensifolii
Bot. Not. 131: 187. 1978.
Herbs, perennial, rhizomatous rhizomatous, orsometimes cespitose. Culms flattened, 2-edged, smooth. Leaves basal and cauline; blade ensiform (flattened with 1 edge facing culm), imperfectly septate. Inflorescences terminal panicles of 2–many heads, sympodial; bracteoles absent proximal to perianth. Flowers in multiflowered heads. Capsules 1-locular, apex separating at dehiscence. Seeds not tailed or occasionally tailed, tegmen reticulate and usually lined. 2n = 20.
w North America, Mexico, e Asia (s to Japan).
Juncus subg. Ensifolii may be polyphyletic. Juncus polycephalus shows affinities with J. scirpoides, J. megacephalus, and J. validus; the remaining members show affinities with J. nevadensis, J. megacephalus, and J. dubius.
Species ca. 7 (6 in the flora).
|1||Capsules cylindric to ovoid, acute to obtuse proximal to beak, 2.7–3.8 mm (including beak): style usually less than 1 mm.||> 2|
|1||Capsules lanceolate to subulate, tapering to beak, 3.3–5.6 mm (including beak); style usually more than 1 mm.||> 3|
|2||Plants robust, usually more than 6 dm; leaves 7–12 mm wide (rarely to 3 mm wide): capsules acuminate, without beak; stamens 6||Juncus xiphioides|
|2||Plants not robust, 2–5 dm; leaves 1.5–6 mm wide; capsules obtuse proximal to beak; stamens 3 or 6||Juncus ensifolius|
|3||Body of capsule included, beak may be slightly exserted.||> 4|
|3||Body of capsule exserted.||> 5|
|4||Capsules rounded proximal to beak; tepals 3–4 mm; inflorescences with 10 or more 6–12-flowered heads||Juncus macrandrus|
|4||Capsules acute proximal to beak; tepals 3.3–4.8 mm; inflorescences variable||Juncus phaeocephalus|
|5||Heads spheric, 20–30-flowered; capsules narrowly lanceolate, apex remaining united after dehiscence||Juncus polycephalus|
|5||Heads hemispheric or narrower, 3–11-flowered; capsules broadly lanceolate, apex usually separating at dehiscence||Juncus oxymeris|