A N F Keys
Amaranthus L.
AMARANTH, PIGWEED
1 Inflorescence of axillary flower clusters throughout the canopy
2 Plants mostly conic with regular 3-dimensional branching, aging spinescent and eventually abscising (tumbleweed); utricle irregularly broken when grasped containing lenticular seed 1−1.1 mm having an encircling rim .. Amaranthus albus [pics]
2' Plants horizontal to ground, not spinescent; utricle dehiscent around circumference (circumscissile)
3 Stems prostrate on ground (freshwater shoreline), cylindric; blades elliptic to ovate or obovate, typically 2−20 × 1.3−12 mm, the smaller leaves on axillary shoots, not folded upward along midrib, light green; tepals 2(−3), on pistillate flower distinctively unequal and 0.4−0.8 mm long; stamens 3, filaments 1−1.2 mm long; utricle tardily dehiscent with cap; seeds lenticular, 0.7−0.9 mm and 0.25 mm thick .. Amaranthus californicus [pics]
3' Shoots procumbent to decumbent forming dense mats, stems with irregular ridges; blades elliptic or obovate to oblong or ovate, 5−40 mm long, relatively small and folded upward on axillary shoots, bluish green; tepals 3−5 and equal, ca. 2 mm long; filaments 1.2−1.6 mm long; utricle easily dehiscent with cap; seeds lenticular, 1.3−1.7 mm and ca. 1 mm thick .. Amaranthus blitoides [pics]
1' Inflorescence terminal in dense, compound clusters of flowers (also some axillary inflorescences)
4 Shoots procumbent to decumbent, typically < 30 cm tall; bractlets subtending flowers 1.2 mm long; tepals 2(−3), unequal, 1−1.5 mm long; utricle indehiscent and somewhat inflated with seed at base; shoots sparsely or densely tomentose on young growth becoming mostly sparsely pubescent with kinky-crisped hairs .. Amaranthus deflexus [pics]
4' Shoots ascending to erect, typically 30−80+ cm tall; tepals 4−5, 1.8−3.5 mm long; utricle dehiscent around circumference (circumscissile)
5 Plants mostly glabrous with some hairs in inflorescence; blades to 65 mm long; bractlets subtending flowers 2−4 mm long; tepals ovate; stamens 4 .. Amaranthus powellii subsp. powellii [pics]
5' Plants conspicuously pubescent throughout; blades often 70−180 mm long; bractlets subtending flowers 1.3−1.8 mm long; tepals obovate; stamens 5 .. Amaranthus retroflexus [pics]
The text of the above keys used with permission from
A Naturalist's Flora of the Santa Monica Mountains and Simi Hills, California
© Copyright
Barry A. Prigge and Arthur C. Gibson
2013