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Genus Lithachne 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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Lithachne (P.Beauv.) is a small, perennial genus of the grass family Poaceae, comprising about five species recognized by Kew’s Plants of the World Online (POWO, 2024) and the World Flora Online (WFO, 2024). The plants are native to South America, occurring chiefly in the wet grasslands, marshes, and riverine savannas of Brazil, with occasional records from northeastern Argentina and Paraguay (Morrone & Zuloaga, 2001). The nomenclatural type is Lithachne axillaris P.Beauv.

Plants are caespitose to rhizomatous perennials with erect to slightly decumbent culms. Leaf sheaths are open, bearing a membranous ligule; blades are linear to lanceolate, glabrous or sparsely pubescent, often with a basal constriction. The inflorescence is a terminal panicle that may be partly enclosed by the sheath. Spikelets are dorsally compressed and bear two florets, the lower reduced and usually sterile, the upper bisexual; the glumes are well developed and equal to spikelet length, and the fertile lemma is hardened and keeled. The ovary is superior with two free styles bearing plumose stigmas, and the fruit is a small caryopsis with a punctiform embryo.

Species diversity is concentrated in the Brazilian Cerrado and Atlantic forest, with one taxon endemic to the high‑elevation grasslands of the southern Amazon basin (POWO, 2024). The genus occurs in seasonally inundated soils from sea level to roughly 1,500 m altitude (Morrone & Zuloaga, 2001). Lithachne follows the typical grass syndrome of wind pollination, and its light caryopses are dispersed mainly by wind and water (Marr et al., 2021).

In recent systematic treatments, Lithachne is placed in the tribe Paspaleae, subtribe Otachyriinae, defined by two‑flowered spikelets and a hardened lemma (Marr et al., 2021). Molecular phylogenies support its monophyly and close relationship to Otachys and Sphacelotheca, reinforcing the generic status despite earlier proposals to merge it with Paspalum (Zuloaga & Morrone, 1994; Morrone & Zuloaga, 2001). No subgeneric sections are currently recognized.

Human relevance is modest; a few species are cultivated as ornamental grasses in tropical gardens and sometimes appear as weedy in managed pastures, but they are not listed as invasive (Morrone & Zuloaga, 2001). Conservation data are scarce; preliminary assessments indicate that habitat conversion for agriculture threatens several species, suggesting a need for detailed field surveys and red‑list assessments. Continued taxonomic clarification and targeted conservation planning will be essential to safeguard the future of this under‑explored lineage.

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