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Aquatic and Wetland Vascular Plants of the Northern Great Plains

Amaranthus L. -- Pigweed


Dioecious (in those treated here) and monoecious annual herbs with taproots, usually branched, erect to spreading, often weedy. Leaves simple, alternate, entire or sinuate-margined, petiolate, exstipulate. Inflorescence of dense terminal and often axillary spikes (actually spikelike thyrses) or clusters. Flowers individually small, subtended by a few bracts, the flowers and bracts greenish or sometimes strongly purple; sepals 1-5 (none in female flowers of A. tuberculatus), scarious or membranous, often resembling the subtending bracts, usually aristate or mucronate; stamens 5, free; stigmas (2)3 or 4, style short or obsolete, ovary superior, 1-celled, short and broad. Fruit a utricle, circumscissile or irregularly splitting; seed round, lenticular, smooth and shiny.

The best known members of the genus are common weeds of fields and disturbed areas, e.g., Amaranthus retroflexus L., rough or redroot pigweed, and A. albus L., tumbleweed. Unlike the water hemps treated here, these pigweeds are monoecious. They are sometimes encountered on shores or drawdown zones. Hybrids in Amaranthus, even between monoecious and dioecious species, are apparently frequent.

Lead Characteristic Go To
1 Plants pistillate. Lead 2
1 Plants staminate. Lead 3
2 Sepals 1 or 2, when 2 then one rudimentary; utricle circumscissile, with a distinct line of dehiscence around the middle. A. rudis
2 Sepals none or rarely 1 or 2 rudimentary ones; utricle splitting irregularly, without a distinct line of dehiscence. A. tuberculatus
3 Outer sepals with midveins excurrent into a mucronate or aristate tip. A. rudis
3 Outer sepals with midveins not excurrent, acuminate to the tip. A. tuberculatus


13. Amaranthaceae, the Pigweed Family
1. Amaranthus L. -- Pigweed
1. Amaranthus rudis Sauer -- Water hemp
2. Amaranthus tuberculatus (Moq.) Sauer -- Tall water hemp


Return to Family -- Amaranthaceae - The Pigweed Family
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