Weeds Identification Gallery

Redstems

  • Ammannia spp.
  • Loosestrife Family Lythraceae
Updated: 01/2026

Redstems, which include purple ammania, Ammania robusta, and other Ammania species are aquatic, broadleaf annuals that reproduce by seed and emerge through the water’s surface. In rice, they thrive where the stand is thin and do especially well during warm years.

Seedling

Cotyledons (seed leaves) are triangular and dark green. The first pair of true leaves is oval or triangular. Leaves are opposite to one another along the stem.

Seedling showing dark green, triangular leaves; . Credit: Jack Kelly Clark, UC IPM
Seedling. Credit: Jack Kelly Clark, UC IPM

Mature Plant

Plants range from 5 to 30 inches (12.5–75 cm) tall. Stems are square in cross-section and branch extensively. Leaves are long, narrow, stalkless, and are opposite to one another along the stem.

Mature plant showing long, narrow leaves opposite each other on stem; . Credit: Jack Kelly Clark, UC IPM
Mature plant. Credit: Jack Kelly Clark, UC IPM

Flowers

Flowers are small, four petaled, bright rosy red, and grow in groups of three to four where the leaf stalks meet the stem.

Flower clusters at leaf axils showing rose petals, 1X; . Credit: Jack Kelly Clark, UC IPM
Flowers. Credit: Jack Kelly Clark, UC IPM
Purple ammannia (Ammannia coccinea) flowering stem. Credit: Joseph M. DiTomaso, UC Agriculture and Natural Resources
Flowering stem. Credit: Joseph M. DiTomaso, UC Agriculture and Natural Resources
Fruit clusters on stem, 1X; . Credit: Jack Kelly Clark, UC IPM
Fruit. Credit: Jack Kelly Clark, UC IPM
Purple ammannia (Ammannia coccinea) seeds. Credit: Jack Kelly Clark, UC IPM
Seeds. Credit: Jack Kelly Clark, UC IPM

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