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Genus Mesosetum in Family Poaceae

In botanical taxonomy, a genus (plural genera) is a rank used to group closely related species within a family. In the hierarchy, genus sits below family and above species.

Genera are defined by shared morphological, anatomical, and genetic characteristics (for example, features of flowers, fruits, seeds, or leaves) that indicate a close evolutionary relationship among the species they contain.

Each genus can include one or more species. Examples include Rosa (roses) and Solanum (nightshades, including tomato and eggplant).

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Genus Description

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Mesosetum (family Poaceae, tribe Paspaleae) is a small genus of grasses comprising roughly 13 species (POWO, 2024; WFO, 2024). It is typified by Mesosetum rottboellioides (Kunth) Steud., as designated in the original protologue. The plants occur in tropical and subtropical South American savannas, with records in Brazil, Argentina, Paraguay, Uruguay and Bolivia, and generally occupy open grasslands, campo rupestre and seasonally inundated pan‑depressions.

Mesosetum species form caespitose clumps with narrow leaf blades and keeled sheaths. Their terminal, open panicles bear dorsally compressed spikelets; the lower glume is usually absent, the upper glume exceeds the floret, and lemmas are awned or awnless with a callus. Ovary is superior with basal placentation, maturing into a small caryopsis (Filgueiras & Lima, 2014).

Species richness peaks in the Brazilian Cerrado, where endemics inhabit sandy, fire‑prone soils. M. rottboellioides and M. panicoides are widespread on the plateau, while M. setifolium is limited to southern campos. Additional taxa occur in Pantanal and the campos of the Sierra de la Ventana, reflecting a pattern linked to the Guiana and Brazilian shields (GPWG II, 2022).

Like other Poaceae, Mesosetum species are wind‑pollinated; anthers dehisce before stigmas become receptive. Seeds are dispersed by wind and, in flood‑prone sites, by water; their light weight aids long‑range transport. Chromosome numbers are based on x = 9, with documented counts of 2n = 36 in M. rottboellioides and 2n = 54 in M. panicoides (Filgueiras & Lima, 2014). Most populations are perennial, persisting as vegetative clumps through seasonal drought.

Molecular phylogenies place Mesosetum within Paspaleae, sister to a clade containing Axonopus and Paspalum (GPWG II, 2022). No subgeneric groups; “setiferous” and “glabrous” assemblages are defined by lemma awn length (Filgueiras & Lima, 2014). Revisions transferred Axonopus species to Mesosetum. Alternative treatments treat Mesosetum as a subgenus of Axonopus (Zuloaga & Morrone, 1999), yet databases accept the concept (POWO, 2024; WFO, 2024).

Few Mesosetum species are cultivated as ornamental grasses, prized for their awned panicles. The genus is not used as a crop, though clumps in pastures may act as weeds reducing livestock forage quality. Local restoration projects in the Cerrado often plant Mesosetum to stabilize soils and support native fauna.

Habitat conversion to cropland, intensive grazing, and altered fire regimes threaten many Mesosetum populations, and the genus remains largely unassessed by the IUCN. Targeted surveys are priorities to safeguard genetic diversity of endemics. Integration of phylogenetic data will refine species limits and guide future management (GPWG II, 2022).

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