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AMARANTHACEAE AMARANTH FAMILY

Mihai Costea, except as noted

Annual to subshrub; monoecious and/or dioecious; occasionally spiny; hairs simple (branched). Leaf: blade simple, alternate or opposite, margins entire or serrate; veins pinnate; stipules 0. Inflorescence: axillary or terminal; 3-flowered cymes in dense spikes, heads or panicles; bracts 0 or 1–5, persistent; bractlets 0–2. Flower: bisexual or unisexual, small, green (± white), yellow or purple; perianth parts 0 or (1)3–5, free or fused basally, scarious or hardened, persistent; stamens 1–5, opposite perianth parts, free or basally fused as a tube, generally unequal, occasionally alternate with appendages on stamen tubes (pseudostaminodes), anthers 2- or 4-chambered; ovary superior, chamber 1; ovule 1 (2–many); style (0)1–3, stigmas 1–3(5). Fruit: utricle; generally with persistent perianth or bracts. Seed: 1 [2+], small, lenticular to spheric, smooth or dotted to striate or tubercled.
± 75 genera, 900 species: cosmopolitan, especially disturbed, arid, saline or alkaline soils; some cultivated for food, ornamental; many naturalized, ruderal or agricultural weeds. [Müller & Borsch 2005 Ann Missouri Bot Gard 92:66–102] Amaranthaceae including Chenopodiaceae by some. Polycnemoideae, represented in California by Nitrophila, formerly considered subfamily of Chenopodiaceae, but needs further research. Guilleminea densa (Willd.) Moq. var. aggregata Uline & W.L. Bray is a waif. Froelichia gracilis (Hook.) Moq. is an historical waif. —Scientific Editors: Douglas H. Goldman, Bruce G. Baldwin.
Unabridged references: [Kadereit et al. 2003 Int J Plant Sci 164:959–986; Robertson 1981 J Arnold Arbor 62:267–313]

Key to Amaranthaceae

AMARANTHUS AMARANTH, PIGWEED
Annual (short-lived perennial herb); monoecious or dioecious. Stem: prostrate to erect, branched or not. Leaf: alternate, petioled, ovate to linear, tip often ± notched (2-lobed), midvein ending in sharp point, margin entire, flat or wavy. Inflorescence: 3-flowered cymes, in dense axillary clusters, or large, terminal, panicle- or spike-like inflorescence; bract 1, bractlets 0–2, alike, persistent, spine-like to ± leaf-like or ± membranous, at least margins scarious-membranous. Flower: unisexual. Staminate flower: perianth parts (2)3–5, scarious; stamens (1)2–5, filaments free; pseudostaminodes 0; anthers 4-chambered. Pistillate flower: perianth parts (1)3–5, membranous or scarious, free, persistent; ovary ovoid, style 0, stigmas 2–3, persistent, slender, papillate; ovule 1, erect. Fruit: circumscissile or indehiscent, ovoid to obovoid, smooth or ± wrinkled, tip ± gradually (abruptly) narrowed to stigmas or beak; walls thin, membranous. Seed: 1, lenticular to ± spheric, round to obovate, smooth, shiny, occasionally obscure-dotted or -net-like, ± white-ivory to brown-red or black.
± 70 species: worldwide; weeds, ornamentals, food plants. (Greek: unfading, non-withering) [Costea et al. 2001 Sida 19:931–974, 975–992; Sauer 1967 Ann Missouri Bot Gard 54:103–137] Hybrids common, F1 generally with numerous, densely packed bractlets beneath generally sterile pistillate flowers, abnormal-shaped inflorescence with dense, twisted or fan-shaped branches. Unless otherwise noted, descriptions of bracts and flower parts are of pistillate flowers.
Unabridged references: [Sauer 1955 Madroño 13:5–46]
Unabridged note: F1 hybrids have been observed in natural conditions or have been experimentally obtained between any of the following species: Amaranthus hybridus, Amaranthus powellii, Amaranthus retroflexus, Amaranthus tuberculatus, Amaranthus palmeri, Amaranthus caudatus, Amaranthus hypochondriacus, Amaranthus cruentus, Amaranthus spinosus, Amaranthus blitoides, Amaranthus albus. Amaranthus caudatus L., Amaranthus cruentus L., Amaranthus hypochondriacus L. frequently cultivated as ornamentals, occasionally escaping from cultivation. Amaranthus spinosus L. probably not naturalized, uncommon waif.

Key to Amaranthus

A. spinosus L. SPINY AMARANTH, THORNY AMARANTH
WAIF
Monoecious. Stem: erect, 2–10(20) dm, simple to many-branched, glabrous or sparsely hairy distally; each node with paired, divergent spines 0.8–1.5(2.5) cm. Leaf: petiole 4–9 cm; blade 20–10(15) cm, 1.5–5 cm wide, ± ovate, base wedge-shaped, tip acute or ± obtuse, margins flat or ± wavy. Inflorescence: axillary, generally of pistillate head-like clusters, and terminal of pistillate clusters and some terminal staminate ± flexible axes, 4–8 cm, 0.4–0.8 cm wide (including flowers), green to silver-green; bracts < perianth parts, spine-like, lanceolate to lance-ovate. Flower: staminate perianth parts 5, 1.5–2 mm, stamens 5; pistillate perianth parts 5, 1.5–2 mm, oblanceolate to spoon-shaped, tip obtuse to spined; stigmas 3, erect to spreading. Fruit: irregular-dehiscent or indehiscent; 1.5–2.2 mm, ± spheric to ovoid. Seed: 0.8–1 mm, lenticular, round, dark brown to black, smooth, shiny.
2n=34. ± rare waif; roadsides, disturbed areas; < 700 m. South Coast, w Mojave Desert; to eastern United States; ± cosmopolitan; native to tropical America. Jun–Oct [Online Interchange]

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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html, accessed on Jul 28 2014
Citation for this treatment: [Author of taxon treatment] 2013. Amaranthus, in Jepson Flora Project (eds.) Jepson eFlora, http://ucjeps.berkeley.edu/cgi-bin/get_IJM.pl?tid=12945, accessed on Jul 28 2014

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Bioregions in which Amaranthus spinosus occurs Markers link to CCH specimen records. If the markers are obscured, reload the page [or change window size and reload]. Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.
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CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa.
Blue line denotes eFlora flowering time.