Evolutionary relationships and taxonomy of Microtea (Microteaceae), a basal lineage in the core Caryophyllales

Abstract

The basal position of the small American genus Microtea within the core Caryophyllales was suggested only recently in accordance with molecular phylogeny. However, the specific relationships within the genus were not traced. The results of our phylogenetic analysis based on the matK chloroplast gene suggest the monophyly of Microtea, and Ancistrocarpus and other related genera should be included in it. Microtea is divided into two major sister clades: clade A consisting of M. glochidiata, M. maypurensis and M. tenuifolia, and clade B comprising M. debilis, M. sulcicaulis, M. scabrida, M. celosioides, and M. papillosa. The nrDNA dataset (ITS), although containing only a limited number of accessions, shows the same species number in clade A, and the remaining species studied (M. debilis, M. scabrida and M. celosioides) form clade B. Subgeneric status is assigned to clades A and B corresponding with the names Microtea subgen. Ancistrocarpus subgen. nov. and Microtea subgen. Microtea, respectively. The diagnostic characters at the subgeneric level are as follows: length of pedicels, number of flowers at each node, number of stamens and styles. A multivariate analysis of 13 distinguishing morphological characters supports the results of phylogenetic analysis. All species have similar pericarp and seed ultrasculpture and anatomy, and they share the reticulate pericarp surface (independent of presence or absence of finger-shaped outgrowths on its surface) and rugose or slightly alveolate seed ultrasculpture. On the basis of morphological characters, we accept 10 Microtea species. A checklist includes a new diagnostic key, morphological descriptions and distribution patterns of each species. Galenia celosioides is the oldest legitimate name available for the plants previously known as Microtea paniculata, for which the combination Microtea celosioides is validated here. The neotypes of Galenia celosioides and Microtea sprengelii were designated from the collections of Prinz Wied at BR. The name M. foliosa is discussed and finally synonymized with M. scabrida. The lectotypes of Ancistrocarpus maypurensis (≡Microtea maypurensis), Microtea debilis var. ovata (=M. debilis), M. glochidiata, M. maypurensis var. angustifolia (=M. tenuifolia), M. glochidiata f. lanceolata (=M. maypurensis), M. longebracteata (=M. celosioides), M. paniculata var. latifolia (=M. scabrida), M. portoricensis, M. scabrida, M. sulcicaulis, and Potamophila parviflora (=M. maypurensis) are designated. Microtea sulcicaulis is reported for the first time as native to Bolivia, and M. maypurensis is reported from Indonesia (Java), where it is found as an alien plant with an unclear invasion status.