Egeria densa Planch.: Waterweed, egeria, Brazilian elodea, anachris. Hydrocharitaceae (frog's bit family).
Non-native perennial. Submersed and rooted in the substrate; multiplying from stem fragments. The firm, crisp stem has relatively few branches and grows to 6 ft (1.8 m). Leaf arrangement is most often in whorls of 4, although groups of 3 to 6 are found; leaves at the base of the stem can be opposite. At intervals along the stem two whorls occur very close together, like one node with twice the usual number of leaves; these double whorls are the only ones that produce branches (one to two branches each) and adventitious roots. Leaves are bright green, thin, shiny and almost translucent. The narrow linear blade is stalkless, up to 1.2 in (3 cm) long and 0.2 in (5 mm) wide, with a single main vein and pointed end. Tiny teeth are found on the leaf margins and toward the tip on the midvein of the underside of the leaf (may require magnification to see). Three-petaled white flowers, up to an inch (2.5 cm) across, are held at the water surface. Compared to hydrilla, a close relative, egeria feels softer and smoother due to the fineness of its foliar teeth. The axillary buds that give rise to side-branches in egeria are large, stiff, and sharply pointed; they are very noticeable when running one's hand down a stem. Widespread and invasive, multiplying vegetatively and creating very dense stands, this is a major nuisance species, obstructing boat traffic and hindering water flow and use.
