baby’s tears, Nuttall's mud-flower, pearl grass
North and Central America, Caribbean
Species commonly cultivated
Hemianthus callitrichoides Griseb. (Micranthemum umbrosum (J.F. Gmel.) Blake (southeastern North America, South America)
H. micranthemoides Nutt. (eastern North America) (Micranthemum micranthemoides)
Annual or perennial. Amphibious. Stem creeping or ascending, rooted at nodes. Leaves opposite, decussate or in whorls of 3-4, sessile; leaf blade orbicular, obovate to ovate, venation indistinct; margin entire. Flowers minute, solitary, zygomorphic, short-pedicellate; sepals fused, lobes 4; corolla tube 1-lipped, abaxial lip 3-lobed; stamens 2-4. Dispersal by stem fragments or seed.
bright sunlight, lakes, rivers, and streams; shallow water and muddy littoral zone
Hemianthus is considered by some authorities as a synonym of Micranthemum, and Hemianthus is sometimes used in the aquarium trade. A fundamental difference between Hemianthus and Micranthemum is the corolla tube lobes; Hemianthus has a one-lipped corolla tube with adaxial lobes absent and a three lobed abaxial lip, while Micranthemum has a two-lipped corolla tube with 3 adaxial lobes and two abaxial lobes united, appearing as one lobe.