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Genus Amaranthus Family Amaranthaceae

Description: Erect or prostrate, annual or perennial, mostly monoecious herbs. Stems rounded or angular, glabrous or hairy.

Leaves alternate, entire, mostly petiolate.

Inflorescence paniculate or spike-like and either terminal with some branches in upper leaf axils, or axillary with the larger clusters in the lower axils. Bracts usually 3 (1 bract and 2 bracteoles) subtending each flower, others subtend inflorescence branches. Flowers mostly unisexual, usually mixed on the inflorescence. Perianth segments 3–5, mostly scarious with a coloured midrib. Stamens 3–5, not necessarily equal to the number of perianth segments. Ovary sessile, circumsciss or indehiscent, sometimes inflated and spongy; styles mostly not developed; stigmas 3, mostly sessile; ovule 1.

Fruit membranous; seed mostly smooth and glossy.

Distribution and occurrence: World: c. 60 species, mostly tropical regions. Australia: c. 20 species (5 species native to mainland), all States.

Text by S. W. L. Jacobs & L. Lapinpuro
Taxon concept:

 Key to the species 
1Perianth segments 32
Perianth segments 57
2Inflorescence axillary, larger clusters in lower axils3
Inflorescence mostly terminal with smaller branches in upper axils only
                       Back to 1
3Bracts with long spines, longer than perianthAmaranthus albus
Bracts with short spines, shorter than perianth
                       Back to 2
Amaranthus macrocarpus
4Fruit much longer (1.3–2 times) than perianth5
Fruit equal to or slightly longer (less than 1.2 times) than perianth
                       Back to 2
5Stems and young leaves with scattered hairsAmaranthus deflexus
Stems and leaves glabrous
                       Back to 4
Amaranthus blitum
6Bracts and perianth segments sharply pointed; bracts longer than perianthAmaranthus powellii
Bracts and perianth segments not sharply pointed; bracts shorter than or equal to perianth
                       Back to 4
Amaranthus viridis
7Inflorescence axillary, larger clusters in lower axils8
Inflorescence mainly terminal with smaller branches in upper axils only
                       Back to 1
8Perianth segments 2–3 mm long19
Perianth segments 5–7 mm long, broad-spathulate
                       Back to 7
Amaranthus grandiflorus
9Inflorescence to 30 cm long, dark red to maroonAmaranthus caudatus
Inflorescence not as above
                       Back to 7
10Two spinescent bracts, 10–15 mm long, present at the base of each short inflorescence branchAmaranthus spinosus
Spinescent bracts absent
                       Back to 9
11Fruit indehiscent or rupturing irregularly12
Fruit circumsciss
                       Back to 10
12Perianth segments oblongAmaranthus muricatus
Perianth segments spathulate
                       Back to 11
13Perianth segments 2–3 mm longAmaranthus mitchellii
Perianth segments 5–7 mm long
                       Back to 12
Amaranthus grandiflorus
14Stems and leaves hairy, especially when young15
Stems and leaves glabrous
                       Back to 11
15Bracts 5–6 mm longAmaranthus retroflexus
Bracts 2–5 mm long
                       Back to 14
16Bracts 3–4 mm longAmaranthus hybridus
Bracts 2–3 mm long
                       Back to 15
Amaranthus cruentus
17Outer perianth segments recurved at the apicesAmaranthus quitensis
Apices of perianth segments straight
                       Back to 14
18Bracts 5–6 mm long; perianth segments 2.5–3 mm longAmaranthus powellii
Bracts 3–4 mm long; perianth segments 1.5–2 mm long
                       Back to 17
Amaranthus hybridus
19Fruit wrinkled, with prominent wavy ribs; confined to river floodplains with grey, brown or blackAmaranthus mitchellii
Fruit wrinkled, without wavy ribs; grows on red sand and rocky areas
                       Back to 8
Amaranthus cuspidifolius

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