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Aquatic and Wetland Vascular Plants of the Northern Great Plains

30. Lythraceae, the Loosestrife Family

1. Ammannia L. -- Toothcup

3. Ammannia robusta Heer & Regel


Simple to widely branching annual 0.5-5(10) dm tall, the lower branches, when developed, usually decumbent, often as long as the erect main stem. Leaves linear-lanceolate to linear-oblanceolate, rarely elliptic to spatulate, 1.5-8 cm long, 2-15 mm wide, mostly auriculate-clasping at the base, sometimes cuneate on lowermost leaves. Inflorescences compact, sessile or essentially so, with 1-3(5) flowers per axil. Calyx tube ca. 3.5 mm long in flower, the lobes alternating with thickened appendages of about the same length; petals 4(-8), pale lavender, sometimes with a deep rose midvein at the base, ca. 2.5 mm long; stamens 4(-12), anthers pale yellow to yellow. Capsules 4-6 mm in diameter at maturity, enclosed by or equaling the calyx. Jul--Oct. Same habitats as the preceding; frequent, se and sc ND, most of SD and NE, rare in e MT and e WY; (OH to s IA and se ND, s to LA and TX, also CA and NM, otherwise scattered in w states; also Mex.)

The great majority of plants in our region formerly identified as A. coccinea are actually A. robusta. Graham (op. cit.) has demonstrated that true A. coccinea (n = 33) is likely an amphidiploid derived from hybridization between A. robusta (n = 17) and A. auriculata (n = 15, 16).

GIF- Species Photo/Drawing
Ammannia robusta, with enlargement of an axillary fruit cluster.
GIF- Distribution Map

Map key


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