Trifolium striatum L. (knotted clover)

Pl. 409 d, e; Map 1821

Plants annual, taprooted. Stems (5–)10–50 cm long, erect or ascending, sometimes from a spreading base, unbranched to much-branched, with long, spreading, shiny hairs. Leaves long-petiolate toward the stem base to nearly sessile toward the tip, the longest petioles to 10 cm, mostly longer then the leaflets. Stipules longer than to often shorter than (near the stem tip) the associated petiole, ovate to narrowly ovate, fused to about the midpoint, the free portions abruptly long-tapered toward the tip, mostly membranous with green or red veins, the margins mostly entire. Leaflets 5–20 mm long, 3–17 mm wide, narrowly obovate, oblong, or oblong-lanceolate, angled at the base, bluntly pointed to more or less truncate or shallowly notched, usually with a small broad tooth at the very tip, the margins finely toothed, the surfaces silky-hairy. Inflorescences 8–20 mm long, 6–15 mm wide, ovoid or oblong-ovoid, becoming elongate and more or less cylindric with age, the stalk absent or inconspicuous (1 or 2 heads closely subtended by a bractlike leaf). Flowers 50–120, sessile or nearly so, ascending at fruiting. Calyces 4–7 mm long, tube 2–4 mm, appressed-hairy, the teeth shorter than to about as long as the tube, unequal (the lowermost tooth usually noticeably longer than the others), narrowly triangular to nearly linear, tapered, with 10 prominent longitudinal nerves but lacking noticeable coss-nerves, becoming inflated (globose to urn-shaped) at fruiting. Corollas 4–7 mm, shorter than to about as long as the calyx lobes, pink, the banner outcurved, oblong, rounded to shallowly notched at the tip, inconspicuously nerved. Fruits 3.0–4.5 mm long, obovoid, sessile or nearly so, the outer wall membranous to papery, 1-seeded. Seeds 1.2–1.5 mm long, oblong-ovoid to nearly globose, reddish brown, shiny. 2n=14. May–August.

Introduced, uncommon, known thus far only from Scott County (native of Europe, Asia; introduced in North America mostly along the eastern and western seaboards). Lawns and open disturbed areas.

Knotted clover is known from relatively few collections in North America. The first Missouri record was collected by Bill Summers in 1992. In nature, T. striatum is a morphologically variable species, and numerous varieties have been described. However, Zohary and Heller (1984) concluded that none of these is worthy of taxonomic recognition.