4. DIDIPLIS Rafinesque, Atlantic J. 1: 177. 1833.
Water purslane or starwort [Derivation uncertain; Greek dis, twice, and diploos, double, possibly alluding to 2 stamens in 4-merous floral tube, or to 2-stamened Didiplis, segregated from 6-stamened Peplis]
Shirley A. Graham
Herbs, annual or short-lived perennial, aquatic or amphibious, 0.5–4 dm, glabrous throughout. Stems erect, creeping, floating, or submerged, irregularly branched, frequently rooting at nodes when submerged. Leaves usually opposite, sometimes subalternate or whorled, dimorphic; sessile or subsessile; blade linear when submerged, narrowly elliptic to lanceolate when aerial, base truncate when submerged, tapered when aerial. Inflorescences indeterminate, flowers solitary, axillary, opposite. Flowers sessile, actinomorphic, monostylous; floral tube perigynous, broadly campanulate; epicalyx segments absent; sepals 4, broadly deltate, 1/2 floral tube length; petals 0; nectariferous tissue present at ovary-floral tube junction; stamens 2–4; ovary 2-locular; placenta globose; style sturdy, relatively short; stigma capitate. Fruits capsules, walls thin and dry, indehiscent, splitting irregularly. Seeds ca. 25, narrowly obovoid to fusiform, slightly convex-concave; cotyledons ± complanate.
Species 1: c, e United States.
Didiplis is easily overlooked due to its undistinguished aspect. In the past it has been included in Ammannia, Lythrum, and Peplis. Molecular evidence now strongly supports the sister relationship of Didiplis to Rotala (J. A. Morris et al. 2007).