Dalea multiflora (Nutt.) Shinners (round-headed prairie clover)

D. candida Michx. ex Willd. var. multiflora (Nutt.) Rydb.

Kuhnistera multiflora (Nutt.) A. Heller

Petalostemon multiflorum Nutt.

Pl. 392 a, b; Map 1731

Plants perennial herbs, with a dark brown to black caudex above a thick, branched root system. Stems 5 to numerous, 30–60(–80) cm tall, erect or ascending, well-branched often mostly toward the tip, rounded to finely ridged, glabrous, sparsely gland-dotted. Leaves 1.5–4.0 cm long, usually not appearing in fascicles. Leaf blades with the rachis 5–14 mm long, gland-dotted, with 5–11 leaflets. Stipules 0.5–2.0 mm long. Leaflets 3–7(–13) mm long, 1–2 mm wide, relatively uniform over the length of the stem, narrowly oblong to oblong-oblanceolate or oblanceolate, tapered at the base, mostly rounded to broadly angled at the tip, but often with a minute, sharp extension of the midvein at the tip, the upper surface glabrous, the undersurface gland-dotted but otherwise glabrous. Inflorescences dense spikes (the axis not visible between the flowers), 7 to more commonly numerous per stem, 0.5–1.5 cm long, headlike, broadly oblong to nearly globose, the stalk 2–6 cm long, the axis glabrous (viewing the axis requires removal of flowers or fruits), with a few inconspicuous bracts and a whorl closely subtending the spike, these persistent, 1–2 mm long, 0.8–1.2 mm wide, tapered to short-tapered above an oblong to obovate base, usually reddish-tinged, usually not gland-dotted, grading into the bracts subtending flowers, these inconspicuous in bud and shed early, 1.5–2.5 mm long (shorter than the calyces of the associated buds), 0.8–1.5 mm wide, short-tapered above an oblong-obovate to obovate base, not gland-dotted, usually strongly reddish-tinged. Calyces with the tube 2.0–2.4 mm long, glabrous, the ribs green, gland-dotted around the rim, the lobes 1.0–1.4 mm long, triangular, with a gland at the tip, the margins minutely hairy. Petals white, the banner with the expanded portion 2.0–2.5 mm long, the wing and keel petals similar, attached along the rim of the stamen tube, the expanded portion 2–3 mm long. Stamens 5, the filament tube 2.0–2.4 mm long, the free filaments 2–3 mm long, the anthers yellow. Fruits included in the persistent calyx or more commonly somewhat exserted, 2–3 mm long, firm and gland-dotted above the membranous basal portion. 2n=14. June–August.

Possibly introduced, uncommon, known thus far from Jackson and Polk Counties and the city of St. Louis (Colorado and Nebraska south to Texas; Mexico). Upland prairies; also railroads.

Dalea multiflora is distinguished from D. candida by the many branches, small globose spikes, smaller leaves and leaflets, and smaller bracts. The two species have overlapping ranges and possibly form hybrids (Wemple, 1970). Their flowers are very similar.

Round-headed prairie clover is quite rare in Missouri, known mostly from along railroads. The single Polk County specimen (Timme 540 at the Missouri State University herbarium) originated from La Petite Gemme Prairie Natural Area, where it has not been rediscovered since the original collection in 1980 despite numerous searches by several botanists. The plant may have been a chance, nonpersisting migrant into this high-quality upland prairie from a railroad track that crosses the western portion of the property.