A revision of Ammannia (Lythraceae) in the Western Hemisphere

Abstract

AMMANNIA L, is a genus of about 25 species of aquatic or marsh-inhabiting herbs distributed in both the Temperate and Tropical zones. It is best represented in Africa (16 species), with a maximum of seven species occurring on each of the other continents. The only monograph of the genus (Koehne, 1903) is outdated because of accumulated changes and additions to the taxonomy and nomenclature and the more extensive collections now available. Many species of Ammannid are distinguished from one another by seemingly minor qualitative differences that are difficult to recognize in practice. In some cases, species limits are based more on geographic disjunctions than on morphological distinctions. Relationships of morphologically similar species occurring on different continents are unknown. The need to resolve the confusion surrounding the variability in species in the New World in order to prepare treatments for several floras now underway has stimulated this revision. The difficulty in obtaining viable seeds necessary for biosystematic investigations of the narrowly endemic African and Asian species also prompted restriction of the study to the species occurring in the Western Hemisphere. MORPHOLOGY The genus Ammannia was divided by Koehne (1880b) into two subgenera and two sections. Subgenus Cryptotheca (Blume) Koehne, comprising the single species A. microcarpa DC., is unique in the Lythraceae by virtue of its parietal placentation. The remainder of the genus comprises subgenus Ammannia (for-merly subg. Euammannia Koehne), which is further divided into two sections and four series, all highly artificial in nature. Five species, representing both sections of subgenus Ammannia, occur in the Western Hemisphere. Section Ammannia (formerly sect. Astylia Koehne), with short or included styles, is represented by A. /atifolia L. and the adventive A. baccifera L.; section Eustylia © President and Fellows of Harvard College, 1985.