anacharis, oxygen weed, Brazilian elodea, Brazilian waterweed
Species commonly cultivated
Egeria densa Planch. (Brazil, Uruguay, Argentina)
E. najas Planch. (Brazil, Uruguay, Argentina, Paraguay)
Egeria densa is established in natural waterways in numerous countries around the world. In many countries this species is declared a prohibited noxious weed.
environmental weed in several countries where it is introduced
Perennial, floating or rooted. Elongate stems bear leaves in densely spaced whorls of 4-5 (particularly dense near apex). Leaves scale-like, sessile, linear, slightly recurved, with single mid-vein; margin finely serrate. Inflorescence axillary, of unisexual flowers. Female and male flowers similar in shape, opening above water surface; sepals 3; petals 3, white. Dispersal by seed and stem fragments. Adventitious roots (unbranched) and lateral branches grow only from double nodes (specialized nodes separated by a shortened internode) typically spaced along stems at 6-12 node intervals. Only fragments containing a double node develop into new plants.
still and slow moving water bodies such as large rivers, ponds, and lakes
Egeria densa is one of the most commonly sold aquatic plants for aquaria and ponds; it is marketed as a water oxygenator. Egeria najas is relatively uncommon in the trade and can be distinguished from E. densa by its narrower stems, leaves usually in 5-merous whorls (4-merous in E. densa), usually longer and more strongly recurved leaf blades, and more prominent serrations on the leaf blade margin.