13. Juncus gerardii Loisel. (black grass)

Pl. 96 e, f; Map 370

Aerial stems 10–70 cm tall, closely spaced along branched rhizomes. Leaves with the auricles at the top of the sheaths less than 0.5 mm long, papery, rounded, the leaf blades 3–20 cm long, 0.5–1.0 mm wide, folded longitudinally, or with the edges rolled toward the middle, lacking cross-partitions. Basal leaves few, 1 or 2 of them sometimes lacking leaf blades. Leaves of the aerial stems 1–3 in the lower half of the stems. Inflorescences condensed or less commonly diffuse panicles, the branches mostly flexuous and ascending, the longest leaflike bract at the base shorter than to about as long as the inflorescence. Flowers mostly occurring singly or in loose clusters of 2–3 near the branch tips, 10–80 per inflorescence, each with a pair of small, ovate to broadly ovate, closely subtending bracts. Perianth 2.0–3.5 mm long, the sepals slightly longer than the petals, lanceolate to elliptic, the sepal tips bluntly pointed and often incurved, the petal tips rounded. Stamens 6 per flower. Fruits 2.0–3.4 mm long, about as long as or slightly longer than the perianth, ovate to broadly elliptic in outline, the tip rounded, 3-locular. Seeds 0.5–0.6 mm long, both ends blunt to rounded and darkened. 2n=80, 84. May–August.

Introduced in St. Louis County (native to the northeastern and northwestern coastal U.S., Canada, Europe, Asia; widely established as an escape elsewhere in the U.S.). Railroads.

Stuckey (1980) chronicled the spread of this circumboreal species in the interior of the United States. According to him, this rush is often associated with railroad tracks and moist, saline areas. It was first reported for Missouri by Mühlenbach (1969), based upon collections from a railway yard. However, it may eventually become more common in the state as a result of winter salt deposition along roads and highways, which has created abundant potential habitats for it.