Callitriche heterophylla Pursh
CC = 6
CW = -5
MOC = 47
Family - Plantaginaceae
Habit - Perennial aquatic forb, monecious, rooting at lower nodes.
Stems - Glabrous, submerged in water and often forming mats.
Leaves - Opposite, simple, dimorphic. Terminal, floating leaves appearing in small rosettes, with blades spatulate, dark green above and lighter green underneath. Lower stem leaves linear.
Inflorescences - Axillary, sessile, with staminate and pistillate flowers sometimes both present in a single axil.
Flowers - Unisexual, minute, lacking both petals and sepals. Staminate flowers with a single stamen, the filament glabrous. Pistillate flowers hypogynous, the ovary 4-locular. Styles 2.
Fruits - Schizocarps, 0.5-1.0 mm, each breaking into 4 mericarps.
Flowering - February - November
Habitat - Spring branches, streams, ponds, sloughs, ditches, swamps.
Origin - Native to the U.S.
Lookalikes - None close.
Other info. - Despite its small size, this aquatic plant is often noticed due to its unique appearance and, usually, the lack of other vegetation competing for visual attention. It is notable for having two leaf morphologies. Upper leaves floating on the surface of the water are borne in rosettes and are spatulate in shape. Submerged leaves on lower portions of the stem are linear and opposite on the stem. Flowers are borne in the leaf axils, but these are tiny and difficult to examine without a good microscope. The plant can be found both in fresh spring water and in stagnant ponds.
Photographs taken near Greer Springs, Oregon County, MO, 6-15-2023 (SRTurner).