Amorpha canescens Pursh (lead plant)

A. canescens f. glabrata (A. Gray) Fassett

A. brachycarpa E.J. Palmer

Pl. 388 g–i; Map 1708

Plants small shrubs or subshrubs, from a knotty rootstock with a deep thick taproot. Stems 30–70(–90) cm tall, unbranched or sparsely branched, usually densely pubescent with short whitish to gray woolly hairs, rarely nearly glabrous, also sparsely and obscurely glandular. Leaves with 29–41 leaflets, subsessile, the petiole 0.5–1.0 mm long, much shorter than the width of the lowest leaflet, the rachis 8–13 cm long, the petiole and rachis densely pubescent with short whitish to gray woolly hairs. Leaflets 9–17 mm long, 4–8 mm wide, ovate-oblong to elliptic, rounded to cordate at the base and with a stalk 0.5–1.0 mm long, rounded or abruptly short-tapered to a minute sharp point at the tip, the margins entire, both surfaces sparsely to more commonly densely pubescent with short whitish to gray woolly hairs, also inconspicuously gland-dotted. Inflorescences 8–17 cm long, mostly in the upper leaf axils, commonly in clusters of 7–9, the flower stalks 0.8–1.2 mm long. Calyces with the tube 1.5–2.0 mm long, the lobes 1.5–2.0 mm long, all similar in size and shape. Corollas with the banner 4–5 mm long, 2.0–2.5 mm wide, obovate, folded around stamens and pistil, bluish purple to purple. Stamens with the free portion of the filaments 4–5 mm long, the anthers 0.3–0.5 mm long, yellow. Ovary 1.0–1.5 mm long, densely hairy, the style 2–3 mm long, glabrous or densely hairy. Fruits 3–4 mm long, 1.2–1.5 mm wide, exserted beyond the persistent calyx tube, hairy and gland-dotted. Seeds 2.0–2.4 mm long, 1.0–1.4 mm wide, olive to reddish brown. 2n=20. May–August.

Scattered nearly throughout the state (Montana to New Mexico east to Michigan and Louisiana; Canada). Upland prairies, loess hill prairies, glades, tops of bluffs, savannas, and openings of dry upland forests; also pastures, railroads, and roadsides.

This showy species is a characteristic element of high-quality prairies in Missouri. In the typical form, the whitish gray plants with their contrasting purple inflorescences are striking and easily recognized. However, occasional plants with much sparser pubescence may be encountered nearly throughout the range. One such nearly glabrous variant in southwestern Missouri that also had slightly broader fruits and somewhat broader leaflets was described as a separate species, A. brachycarpa (Palmer, 1931), but too many intermediates with typical A. canescens exist to allow formal taxonomic recognition of this form (Wilbur, 1964, 1975; Isely, 1998). For a discussion of a putative hybrid with A. fruticosa, see the treatment of that species.

Amorpha canescens was once considered an indicator of lead ore in Wisconsin and Illinois. The flowers are protogynous, that is, the style matures in the flowers before the stamens. This beautiful species is well-adapted to sunny sites in the garden and is available commercially through many wildflower nurseries.