3. Amaranthus blitoides S. Watson (tumbleweed, prostrate amaranth, spreading pigweed)
Pl. 198 f; Map
812
Plants
monoecious. Stems 10–70 cm long, spreading to less commonly loosely ascending,
often forming dense mats, glabrous or sparsely pubescent with inconspicuous,
mostly multicellular hairs, unarmed. Leaves short- to long-petiolate. Leaf
blades 0.5–2.0(4.0) cm long, oblong-elliptic to obovate, rounded or shallowly
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 rarely also present. Bracts 1.0–2.5 mm long, those of the
pistillate flowers about as long as 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 sometimes extending beyond the main body as a minute awn,
somewhat spinelike at maturity. Staminate flowers with 4 or 5 more or less
similar sepals, these 1.3–2.0 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
4 or 5 sepals (the inner sepals somewhat shorter and narrower than the outer
ones), these 1.2–2.7 mm long, erect or somewhat outward-curved, lanceolate to
ovate or narrowly oblong-elliptic, narrowed or tapered to a blunt or sharp
point. Stigmas 3, spreading. Fruits 1.5–2.1 mm long, with circumscissile
dehiscence, the surface smooth or nearly so when dry. Seeds 1.3–1.7 mm in
diameter, rounded along the rim, the surface black. 2n=32. July–October.
Scattered nearly
throughout Missouri, but uncommon to absent in the southeastern quarter of the
state (western U.S. [including Alaska] east to North Dakota and Texas; Canada;
introduced eastward to Maine and Florida, as well as to Mexico, Caribbean
Islands, Europe, and Asia). Banks of streams and rivers, bases of bluffs, and
talus slopes; also roadsides, railroads, pastures, and open, disturbed areas.
Steyermark
(1963) and many earlier authors called this species A. graecizans L.,
but that name has been shown to apply to a species native to the Mediterranean
region with only two North American records (from New Jersey), apparently from
plants introduced in ship’s ballast during the nineteenth century (Sauer and
Davidson, 1961; Costea et al., 2001b).