Micranthemum

Scientific name

Micranthemum Michx.

Common names

baby’s tears, shade mudflower, pearl grass

Family

Scrophulariaceae

Native distribution

North and Central America, Caribbean

Species commonly cultivated

Micranthemum umbrosum (Walter) S.F. Blake (eastern and southern North America)

Adventive distribution

none

Weed status

not weedy

Habit

small, emergent, and amphibious creeping stem plant

Brief description

Annual or perennial. Stem amphibious, creeping or ascending, rooted at nodes. Leaves opposite, decussate or in whorls of 3 to 4, sessile; leaf blade orbicular, obovate to ovate, venation indistinct; margin entire. Flowers minute, solitary, in leaf axils, zygomorphic, short-pedicellate; calyx tubular, lobes 4; corolla tubular, white, 2-lipped, abaxial lip short, emarginate, of 2 united lobes; adaxial lip 3-lobed; stamens 2-4. Dispersal by stem fragments or seed.

Natural habitat

bright sunlight, lakes, rivers, and streams; shallow water and muddy littoral zone

Additional comments

Hemianthus Nutt. 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 in the number of corolla tube lobes; Hemianthus has a 1-lipped corolla tube with adaxial lobes absent and a 3-lobed abaxial lip, Micranthemum has a 2-lipped corolla tube with three adaxial lobes and the two abaxial lobes united, appearing as one lobe.