2. Amaranthus arenicola I.M. Johnst. (sandhills pigweed, sandhills amaranth)
Pl. 197 e, f;
Map 811
Plants
dioecious. Stems 50–200 cm long, erect or ascending, glabrous or nearly so,
unarmed. Leaves mostly long-petiolate. Leaf blades 1–8 cm long, narrowly
oblong-lanceolate to oblong-elliptic, narrowed or tapered to a bluntly or sharply
pointed tip, narrowed or tapered at the base, glabrous. Inflorescences dull or
grayish green, occasionally dull reddish-tinged, mostly terminal, the axillary
inflorescences mostly elongate spikes, the terminal inflorescence a panicle
with few to numerous ascending branches, the flowers often grouped into
discontinuous clusters or regions along the basal portions of the spikes, the
tip usually straight or nearly so at maturity, the main axis and branches
glabrous or nearly so. Bracts 1.5–2.5 mm long, shorter than (in staminate
plants) to about as long as (in pistillate plants) the sepals, lanceolate to
narrowly ovate, narrowed or tapered to a sharply pointed tip, with a somewhat
thickened green midrib and relatively broad, thin, papery margins, the midrib
not or only slightly extending beyond the main body as a minute, sharp point.
Staminate flowers with 5 more or less similar sepals, these 3–5 mm long, erect
or very slightly outward-curved, lanceolate to oblong-elliptic, narrowed to a
minute, sharp point at the tip, the inner ones otherwise bluntly pointed to
shallowly and minutely notched, the outer ones bluntly to sharply pointed.
Stamens 5. Pistillate flowers with 5 sepals, these outward-curved at the tip,
oblanceolate to spatulate, rounded or bluntly pointed at the tip, the midrib
not or only slightly extending beyond the main body as a minute, sharp point,
the inner ones 1.5–2.0 mm long, the outer ones 2.0–2.5 mm long, bluntly pointed
at the tip. Stigmas 2(3), spreading. Fruits 1.4–1.7 mm long, circumscissilely
dehiscent at about the midpoint, the surface smooth when dry. Seeds 1.0–1.3 mm
in diameter, rounded along the rim, the surface reddish brown to black. 2n=32.
June–October.
Introduced,
known only from the St. Louis and Kansas City metropolitan areas (native of Iowa to Wyoming south to
Texas and New Mexico;
introduced eastward to Virginia and New Jersey and westward to California). Railroads and open, sandy,
disturbed areas.
The name A.
torreyi (A. Gray) Benth. ex S. Watson, used for this species by most
earlier authors (Steyermark, 1963), was originally described based on a mixture
of specimens now referred to several western Amaranthus species and long
misapplied to A. arenicola (Sauer, 1955).