Pigweeds  (Amaranthus spp.)

Pigweeds are erect summer annual plants that germinate from seeds during late winter through summer. Several species occur, but the most common is redroot pigweed.

Seedling

Seedlings of all common pigweeds are similar. Cotyledons (seed leaves) are long and narrow and are often red underneath.

Mature plant

Prostrate pigweed (bottom, right in photo) forms dense mats, has dark glossy green leaves with distinctive light colored edges, and often pink or red tinged stems. Tumble pigweed is bushy with light green leaves.

Flowers

Tumble pigweed (top, left) flower clusters only grow between the stem and leaf stalks, rather than in spikes as found in other pigweeds such as palmer amaranth (top, right).

Fruits

The single-seeded fruits are tiny capsules, roughly less than 1/17 of an inch (1.5 mm) long and open around the middle by a caplike lid to release the seed.

Seeds

Seeds are round, roughly 1/25 to 1/17 inches (1–1.5 mm) in diameter, glossy, and dark reddish brown to black.

Reproduction

In general, pigweeds reproduce by seed. In low amaranth, new shoots can grow from upper portions of a taproot and crown that remain in the soil after cultivation.

Related or similar plants

• Redroot pigweed, Amaranthus retroflexus
• Prostrate pigweed, Amaranthus blitoides

More information

• Broadleaf ID illustration
• Calflora distribution map
  • Palmer amaranth, Amaranthus palmeri
  • Smooth pigweed, Amaranthus hybridus
  • Low amaranth, Amaranthus deflexus
  • Redroot pigweed, Amaranthus retroflexus
  • Tumble pigweed, Amaranthus albus
• For agriculture: UC IPM Pest Management Guidelines