21. Juncus tenuis Willd. (path rush, poverty rush)

Pl. 96 k, l; Map 378

Aerial stems 7–80 cm tall, caespitose, lacking noticeable rhizomes. Leaves 3–5, all basal, 1 or 2 of them sometimes lacking leaf blades, the auricles at the top of the sheaths 1.0–3.5 mm long, loose, white, and papery, usually pointed, the leaf blades 10–30 cm long, 0.5–1.5 mm wide, flat, folded longitudinally, or with the edges rolled toward the middle, lacking cross-partitions. Inflorescences condensed or diffuse panicles, the branches mostly flexuous and ascending, the longest leaflike bract at the base longer than the inflorescence. Flowers mostly occurring singly or in loose clusters of 2–6 near the branch tips, 20–70 per inflorescence, each with a pair of small, ovate to triangular, closely subtending bracts. Perianth 2.5–5.5 mm long, the sepals as long as or slightly longer than the petals, lanceolate, the tips attenuate. Stamens 6 per flower. Fruits 2.5–4.5 mm long, slightly shorter to shorter than the perianth, ovate to obovate in outline, the tip usually rounded, 1-locular with 3 incomplete cross-walls protruding about halfway to the middle of the fruit. Seeds 0.3–0.5 mm long, both ends abruptly tapered to darkened points and usually also with short tail-like appendages. 2n=30, 32, 40, 42, 80, 84. May–September.

Common throughout Missouri (native to North America, but naturalized nearly worldwide). Openings of mesic upland forests, stream banks, and margins of ponds and lakes; also paths, and roadsides, fields, pastures, and open, disturbed areas.

This is one of the commonest species of Juncus in Missouri, and it is also one of the most successful rushes to colonize disturbed habitats. It belongs to a taxonomically difficult complex that includes J. brachyphyllus, J. dudleyi, and J. interior, which may be distinguished by the characters presented in the key to Juncus species. Rangewide, a number of variants have been segregated as varieties or formae. Only two of these are recognized in the present treatment.