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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. retroflexus L.

Plant erect, 3–30 dm, monoecious
Leaf: petiole 7–70 mm; blade 20–150 mm, lower diamond-shaped to widely ovate, upper ± lanceolate
Inflorescence: generally panicle of spike-like clusters; axillary clusters generally many, 1–5 cm, ± 1–2.5 cm wide; terminal spike < or = 20 cm, 5 cm wide; bracts 2.5–4.5 mm, spined, midrib wide, green, margins scarious in lower 3/4
Staminate flower: sepals 4–5, 2–3 mm, subequal; stamens (3)4–5
Pistillate flower: sepals 5, 2–3.2 mm, subequal, oblong to spoon-shaped, becoming reflexed, tip rounded to slightly notched, often abruptly pointed
Fruit ± 1.5 mm, circumscissile; lid smooth or wrinkled near base
Seed 1–1.3 mm, black
Chromosomes: n=16
Ecology: Common. Wet fields, roadside ditches, waste places
Elevation: < 2400 m.
Bioregional distribution: Great Central Valley, Central Western California, Southwestern California
Distribution outside California: to se Canada, n Mexico, also Eurasia; native to tropical America

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