Palmer amaranth is a fast-growing, erect, summer annual. It is one of several weedy Amaranthus species found in California. The plant can be found in the San Joaquin Valley, and desert regions of California up to 4000 feet (1200 m). In the Southern United States palmer amaranth is a serious problem due to the development of resistance to multiple herbicides, its rapid growth and competitiveness, and the large number of seeds that each plant produces.
Habitat
Crop fields, orchards, vineyards, and roadsides.
Seedling
Cotyledons (seed leaves) are long, narrow, lance shaped, and often have reddish undersides. It is difficult to distinguish Amaranthus species from each other at the seedling stage.
Mature Plant
Plants are fast growing and can be up to 6.5 feet (2 m) tall. Stems are hairless and coarse. Leaves alternate on the stem, are 0.6 to 6.5 inches (1.5 to 7 cm) long, and are ovate to diamond shaped. Petioles are longer than the leaf blade. Leaves may have a single leaf tip hair or v-shaped white watermark.
Flowers
Flowering occurs from July to November. Spikelike panicles are present at the top of the plant that are unbranched, flexible, 4 to 20 inches (10 to 50 cm) long, and consist only of male flowers or only of female flowers. Large (0.25 inch or 6 mm) bracts are present. The bracts of female flowers harden and become sharp as they mature while male flowers remain soft through maturity.
Seeds
Seeds are small, oval shaped, dark reddish brown to black, smooth, and shiny.
Reproduction
Reproduces by seed.
