A revision of the African genus Mesanthemum (Eriocaulaceae)

Abstract

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.

A monograph of the African and Madagascan species of Cyperus sect. Incurvi (Cyperaceae)

“…), and Cyperus laevigatus L. (type species for the segregate genus Juncellus C.B.Clarke) exemplifies how contrasting morphology may not reflect independent evolutionary history within Cyperaceae, but rather rapid adaptation and diversification (Larridon et al 2013(Larridon et al , 2020. Similar examples can be seen outside Cyperaceae, such as the African Eriocaulaceae genus, Mesanthemum Körn (Liang et al 2019), and in the recircumscription of the Dioscoreales to include the families Burmanniaceae and Thismiaceae in light of morphological synapomorphies which had not previously been considered relevant when constructing the taxonomy of the higher systematic levels of this order (Caddick et al 2002a, b). These types of studies emphasise the importance of integrating molecular and morphological information to identify which traits are phylogenetically informative.…”

Eriocaulaceae: A new classification system based on morphological evolution and molecular evidence

“…The morphology of seed characters was already considered important and with great potential for defining genera in Eriocaulaceae, but was still underexplored in Paepalanthus and allied groups (Giulietti & al., 1987; Nair, 1987; Zona & al., 2012; Barreto & al., 2013; Corredor & al., 2015; Liang & al., 2019; Mascarenhas & Scatena, 2021; Darshetkar & al., 2021). These characters were fundamental in the generic delimitation proposed here, especially in the new circumscription of Paepalanthus , which was difficult to be delimited due to the lack of exclusive morphological characteristics.…”