Northern Prairie Wildlife Research Center
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.
||Sepals 1 or 2, when 2 then one rudimentary; utricle
circumscissile, with a distinct line of dehiscence around the middle.
||Sepals none or rarely 1 or 2 rudimentary ones; utricle
splitting irregularly, without a distinct line of dehiscence.
||Outer sepals with midveins excurrent into a mucronate
or aristate tip.
||Outer sepals with midveins not excurrent, acuminate
to the tip.
13. Amaranthaceae, the Pigweed Family
1. Amaranthus L. -- Pigweed
- 1. Amaranthus rudis Sauer -- Water
- 2. Amaranthus tuberculatus (Moq.)
Sauer -- Tall water hemp
Return to Family -- Amaranthaceae - The Pigweed
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