Eriocaulon is a genus of c. 470 aquatic and wetland species of the monocot plant family Eriocaulaceae. It is widely distributed in Africa, Asia and America, with centres of species richness in the tropics. Most species of Eriocaulon grow in wetlands although some inhabit shallow rivers and streams with an apparent adaptive morphology of elongated submerged stems. In a previous molecular phylogenetic hypothesis, Eriocaulon was recovered as sister of the African endemic genus Mesanthemum . Several regional infrageneric classifications have been proposed for Eriocaulon . This study aims to critically assess the existing infrageneric classifications through phylogenetic reconstruction of infrageneric relationships, based on DNA sequence data of four chloroplast markers and one nuclear marker. There is little congruence between our molecular results and previous morphology-based infrageneric classifications. However, some similarities can be found, including Fyson’s sect. Leucantherae and Zhang’s sect. Apoda . Further phylogenetic studies, particularly focusing on less well sampled regions such as the Neotropics, will help provide a more global overview of the relationships in Eriocaulon and may enable suggesting the first global infrageneric classification. Electronic supplementary material The online version of this article (10.1007/s10265-019-01129-3) contains supplementary material, which is available to authorized users.

Mesanthemum is a genus comprising 16 species in the family Eriocaulaceae and is native to Africa and Madagascar. Eriocaulaceae are characterised by a basal tuft or rosette of narrow leaves and small flowers in heads. Mesanthemum can be recognised by diplostemonous flowers and fused glandular pistillate petals. While most Mesanthemum species are large perennial herbs, two small ephemeral species from West Africa, M. albidum and M. auratum differ from the rest of the genus by their shorter life cycle, smaller size, simpler floral structures and different seed surface patterning. A molecular phylogenetic study, morphological comparisons and scanning electron microscope (SEM) examination of seed coat sculpture were carried out to determine whether they should be separated as a new genus. The molecular results indicate that the two ephemeral species are nested in the Mesanthemum clade. However, they are not closely related to each other. All species of Mesanthemum are here revised, including the description of a new species M. alenicola from Equatorial Guinea. An identification key is provided, together with taxonomic descriptions, synonymy and notes. Images of the seeds as seen under SEM are provided where available. Lectotypifications are provided for Mesanthemum albidum, M. bennae, M. pilosum, M. prescottianum, M. pubescens and M. variabile. A neotype is selected for M. rutenbergianum, which is synonymised with M. pubescens.Fig. 4. Maximum likelihood analysis based on concatenated alignment for four plastid regions (matK, rbcL, rpoB and rpoC1) and one nuclear region (PHYC). Bootstrap (BS) values are shown.