Northern Prairie Wildlife Research Center
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).
Ammannia robusta, with enlargement of an axillary fruit cluster.
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