1. Amaranthus albus L. (tumbleweed)

A. albus var. pubescens (Uline & W.L. Bray) Fernald

Pl. 198 a, b; Map 810

Plants monoecious. Stems 30–100 cm long, loosely to strongly ascending, often forming dense, irregularly globose masses, glabrous or sparsely to moderately pubescent with inconspicuous, mostly multicellular hairs, unarmed. Leaves short- to long-petiolate. Leaf blades 0.5–4.0(–8.0) cm long, elliptic to obovate, rounded or shallowly and minutely notched at the tip (the midvein sometimes extending as a minute, sharp point), tapered at the base, glabrous. Inflorescences grayish green to green, all or nearly all axillary; mostly dense, small, globose clusters, with a short, terminal spike occasionally also present. Bracts 2.0–2.6 mm long, at least those of the pistillate flowers conspicuously longer than the sepals, lanceolate to oblong-lanceolate, narrowed or tapered to a sharply pointed tip, with a somewhat thickened midrib, green or sometimes with narrow, thin, papery margins, the midrib extending beyond the main body as a short awn, somewhat spinelike at maturity. Staminate flowers with 3 more or less similar sepals, these 1.2–2.3 mm long, erect or very slightly outward-curved, lanceolate to narrowly oblong-elliptic, narrowed or tapered to a minute, awnlike extension of the midrib at the tip. Stamens 3. Pistillate flowers with 3 more or less similar sepals (the third sepal occasionally slightly longer than the other 2), these 0.8–1.2 mm long, erect or very slightly outward-curved, lanceolate to narrowly oblong-elliptic, narrowed or tapered to a blunt or sharp point. Stigmas 3, more or less erect from a thickened base. Fruits 0.9–1.5 mm long, with circumscissile dehiscence, the surface often finely wrinkled when dry. Seeds 0.7–1.0 mm in diameter, rounded along the rim, the surface reddish brown to black. 2n=32. July–October.

Scattered and sporadic, mostly in the western and southern halves of the state (native of North America; introduced widely in Central America, South America, Europe, Asia, and Africa). Banks of streams and rivers, exposed bases of bluffs, and open-soil areas of upland prairies; also roadsides, railroads, margins of crop fields, fallow fields, and open, disturbed areas.

The original distributional limits of this species are poorly understood, but it is generally considered native in Missouri. Hairy plants are encountered occasionally nearly throughout the North American range of the species. These have been called var. pubescens by some authors (Steyermark, 1963) but are unworthy of formal taxonomic recognition.