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AMARANTHACEAE

AMARANTH FAMILY

James Henrickson

Annual to tree
Stem prostrate to erect
Leaves alternate or opposite, simple, generally entire, bract-like upward; stipules 0
Inflorescence: cymes, often arrayed ± in spikes or panicles; bracts 1–3 per flower, generally membranous-scarious, tip often short-pointed or spine-like
Flower generally small, uni- or bisexual, radial; sepals 0–5, fused at base or free, often ± scarious; petals 0; stamens 0–5, opposite sepals (staminodes sometimes alternating), filaments sometimes fused at base; ovary superior, 1-chambered, ovules 1–several, erect or pendent on ± basal stalks, styles 0–3, stigma head-like or 2–3-lobed
Fruit: utricle to circumscissile capsule
Seed lenticular to spheric, hard
Genera in family: ± 65 genera, ± 900 species: tropical, subtropical
Reference: [Robertson 1981 J Arnold Arbor 62:267–313]

AMARANTHUS

PIGWEED, AMARANTH

Annual, monoecious or dioecious
Leaves alternate; blade linear to ovate
Inflorescence: cymes in dense, spike-like clusters; bract 1, tip generally short-pointed or -spined, generally scarious; bractlets 0–2
Staminate flower: sepals 3–5, ± equal, ± as bracts; stamens (1)3–5, filaments free; staminodia 0
Pistillate flower: sepals (3–)5, ± equal, scarious except midvein, fused at base, falling with fruit; ovary compressed-ovoid, styles (2)3, stigmas slender, papillate, ovule 1, erect
Fruit circumscissile or indehiscent, smooth or inflated-wrinkled; walls membranous to spongy-hardened
Seed 1, lenticular, smooth, reddish to black
Species in genus: ± 60 species: worldwide; some potherbs, some cultivated for seed
Etymology: (Greek: unfading, from persistent bracts and sepals)
Some species (especially A. cruentus, A. powellii, A. retroflexus) hybridize complexly
Reference: [Tucker & Sauer Madroño 1958 14:252–261]

Introduced

A. spinosus L.

Plant erect, 2–10 dm, ± spheric, monoecious; spines at lower nodes generally 2, 8–20 mm, slender
Leaf: petiole 12–70 mm; blade 14–80 mm, ± ovate
Inflorescence dense; axillary clusters below middle ± spheric, each with 2 bracts elongated, stiff, spiny; terminal clusters spike-like, 3–17 cm, 4–13 mm wide, cylindric; upper bracts 1.5–6 mm, spine-tipped, midrib thick, green, margin scarious below
Staminate flower: sepals 5, 1.5–2 mm; anthers 5
Pistillate flower: sepals 5, 1.5–2 mm, oblanceolate to spoon-shaped, tip obtuse to spined
Fruit 1.5–2 mm, irregularly dehiscent; lid smooth throughout or base rough
Seed ± 1 mm wide, reddish black
Chromosomes: 2n=34
Ecology: Very uncommon as waif. Roadsides, waste places
Elevation: < 700 m.
Bioregional distribution: South Coast, w Mojave Desert
Distribution outside California: to e US, Mexico; native to tropical America

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