Rotala rotundifolia, or Roundleaf toothcup, is a popular ornamental in the international aquarium industry that has more recently been promoted for water gardens. It is often referred to as “Dwarf rotala” in the trade. It was first collected in 1996 from a flood control canal passing through a residential area in Broward County. Other naturalized populations have been found in Palm Beach County and Lee County. The only other known North American introduction point is Tuscaloosa, Alabama, where it was well-established around a campus pond until the pond was drained and left to dry. Rotala rotundifolia is native to India and Southeast Asia. It is in the same family, Lythraceae, as another aquatic weed, purple loosestrife (Lythrum salicaria).
Rotala rotundifolia is a creeping aquatic perennialwithsoft, dark pink stems that branch often to form low, creeping clumps. Leaves are rounded and attach closely to the stem without a leaf stalk. They are arranged oppositely on the stem. Flowers occur in spikes at the tip of stems. Plants flower prolifically in spring and early summer. Rotala rotundifolia can spread by floating stem fragments, which root adventitiously at lower nodes. The plant also produces viable seeds. Fruits are dry capsules which split open to disperse seeds. Other species of Rotala that occur in North America are the native Rotala ramosior and the introduced R. indica.
2,4-D herbicide formulations have been successful in controlling Rotala rotundifolia. Grass carp present in infested canals do not appear to consume the plant. The species is in Category II of the FLEPPC 2007 List of Invasive Plant Species.
References:
“Rotala rotundifolia (Lythraceae) new to Florida,” by K.C. Burks, D.W. Hall, V.V. Vandiver, C. Jacono. 2003. Sida 20(4):1765-1769.
“Rotala rotundifolia, purple loosestrife of the South?” by C.C. Jacono and V.V. Vandiver. 2007. Aquatics 29(1):4, 6, 8-9.
