A systematic study of two complexes of closely related species within Eleocharis subg. Limnochloa was conducted to better define poorly understood species and to lay the foundation for a worldwide revision of this group. Research utilized scanning electron microscopy (SEM), study of more than 2300 herbarium specimens and types from 35 herbaria, multivariate analysis, and field studies in the southeast United States and Mexico. Examination of achene gross- and micromorphology using SEM indicated a relationship among the species of the Eleocharis mutata complex (comprising E. mutata, E. spiralis, and E. cellulosa), their distinctness from the E. acutangula complex (comprising E. acutangula s.l. and E. obtusetrigona) and support the placement of all taxa studied within subg. Limnochloa. All species examined shared micromorphological characters typical of subg. Limnochloa. A systematic study of the worldwide morphological variation of E. mutata suggests it is represented by a single taxon throughout its distribution and is native to the New World and probably introduced in tropical Africa. The taxonomic relationship of Eleocharis mutata and E. spiralis was explored using discriminant analysis, PCA and phyto-geography, supporting the recognition of the two taxa as distinct at the rank of species. A systematic study of E. cellulosa suggests it is represented by a single taxon throughout its distribution, with an apparent Caribbean genotype distinguished by the presence of perianth bristles with retrorse spinules. A systematic study of the worldwide variation of E. acutangula s.l. resulted in its segregation into two infraspecific taxa, E. acutangula subsp. acutangula and E. acutangula subsp. breviseta, and two new South American species, E. neotropica and E. steinbachii. Nomenclatural history and lectotypification of certain taxa studied are discussed, and two basyionyms and two synonyms of accepted taxa are lectotypified. A taxonomic treatment is provided that includes a key, detailed descriptions and complete synonymy of each species, line drawings prepared from select specimens examined, and notes on habitat and distribution. Future research goals and needs are discussed.

A systematic study of two complexes of closely related species within Eleocharis subg. Limnochloa was conducted to better define poorly understood species and to lay the foundation for a worldwide revision of this group. Research utilized scanning electron microscopy (SEM), study of more than 2300 herbarium specimens and types from 35 herbaria, multivariate analysis, and field studies in the southeast United States and Mexico. Examination of achene gross- and micromorphology using SEM indicated a relationship among the species of the Eleocharis mutata complex (comprising E. mutata, E. spiralis, and E. cellulosa), their distinctness from the E. acutangula complex (comprising E. acutangula s.l. and E. obtusetrigona) and support the placement of all taxa studied within subg. Limnochloa. All species examined shared micromorphological characters typical of subg. Limnochloa. A systematic study of the worldwide morphological variation of E. mutata suggests it is represented by a single taxon throughout its distribution and is native to the New World and probably introduced in tropical Africa. The taxonomic relationship of Eleocharis mutata and E. spiralis was explored using discriminant analysis, PCA and phyto-geography, supporting the recognition of the two taxa as distinct at the rank of species. A systematic study of E. cellulosa suggests it is represented by a single taxon throughout its distribution, with an apparent Caribbean genotype distinguished by the presence of perianth bristles with retrorse spinules. A systematic study of the worldwide variation of E. acutangula s.l. resulted in its segregation into two infraspecific taxa, E. acutangula subsp. acutangula and E. acutangula subsp. breviseta, and two new South American species, E. neotropica and E. steinbachii. Nomenclatural history and lectotypification of certain taxa studied are discussed, and two basyionyms and two synonyms of accepted taxa are lectotypified. A taxonomic treatment is provided that includes a key, detailed descriptions and complete synonymy of each species, line drawings prepared from select specimens examined, and notes on habitat and distribution. Future research goals and needs are discussed.