A revision of the African genus Mesanthemum (Eriocaulaceae)
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ISSN: 0075-5974 (print) ISSN: 1874-933X (electronic)
A revision of the African genus Mesanthemum (Eriocaulaceae) Yuxi Liang1, Sylvia M. Phillips1, Martin Cheek1 & Isabel Larridon1,2
Summary. 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. Key Words. Africa, lectotypifications, Madagascar, molecular phylogenetics, new species, SEM seed images, taxo-
nomy.
Introduction Mesanthemum Körn. belongs to the pantropical and warm temperate monocot family Eriocaulaceae, comprising ten genera and c. 1200 species (WCSP 2018). Most of the generic diversity occurs in South America, especially Brazil (Giulietti et al. 1995; Dokkedal et al. 2008), and the type genus Eriocaulon L. is pantropical, extending into warm temperate parts of Asia, Australia, North America and western Europe. Mesanthemum is unusual in being confined to tropical Africa and Madagascar. It has been little studied from a molecular phylogenetic point of view (Andrade et al. 2010), most previous work being associated with African Flora accounts (e.g. Phillips 1997, 2010, 2011, 2016). The family is characteristically found in permanently or seasonally wet habitats on a variety of substrates (Stützel 1998: 203), often favouring sandy soils. A few species, including M. reductum H.E.Hess, are true aquatics, occurring in rivers and lakes. Mesanthemum was last revised by Jacques-Félix (1947), who recognised 10 species. Since then, new material has been collected, and several new species have been described (Hess 1955; Kimpouni 1994;
Moldenke 1949) bringing the total to 16 accepted species (WCSP 2018). The genus is morphologically well defined, most species being robust perennials with scapes up to c
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