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Genus Lasiacis 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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The scrambling grasses of Lasiacis (Poaceae: Panicoideae) form a Neotropical genus of about fifteen species that climbs, roots at nodes, and often forms clonal thickets in forest edges and second growth. Many species are lowland and mid-elevation inhabitants of shaded to semi‑shaded habitats; the genus ranges widely through tropical America and the Caribbean. The name was validated by Hitchcock as a segregate of Panicum, and it is typified by Lasiacis ligulata (Hitchcock) in later lectotypifications (Peterson et al., 2015; Soreng et al., 2017/2023; WFO, 2024).

Lasiacis is distinguished by a woody, scrambling habit with rhizomes or stolons and robust culms that root at the nodes. Leaves are usually broad and firm, often with conspicuous paired basal sheaths that swell around buds. The inflorescence is an open panicle; spikelets are borne in pairs on unequal pedicels and bear a reduced lower glume that is one‑third to one‑half the length of the spikelet. The lower lemma is indurated, and the fruit is a caryopsis with a linear hilum (Davidse & Peterson, 1999).

Diversity is highest in the Greater Antilles, with multiple island endemics; several species occur on the mainland from Mexico to northern South America. Habitats span wet forest understories, thickets, coastal scrub, and secondary growth, where the plants often serve as structural pioneers. Wind pollination predominates, but cleistogamous spikelets occur in some taxa; dispersal appears to be largely local by gravity and animal movement, though consistent field documentation remains sparse (Davidse & Peterson, 1999). A base chromosome number of x = 9 is well supported across multiple species (Davidse & Peterson, 1999).

Recent systematic work has refined internal groupings, traditionally treated as sections or informal series; modern treatments retain Lasiacis separate from Panicum and Oplismenus, emphasizing spikelet and habit differences (Peterson et al., 2015; Soreng et al., 2017/2023). Species boundaries are obscured by plasticity and possible hybridization; L. sorghoides is sometimes placed in Chusquea in alternative treatments (WFO, 2024). The genus contributes little to agriculture, but several species are ornamental or structural plants in tropical horticulture; none are major weeds of agriculture.

Habitat loss and island endemism drive conservation concern for several taxa, though most are widespread where habitats remain. Integrated phylogenomics and field‑based mating‑system studies are priorities to resolve species limits and clarify the evolutionary significance of climbing in tropical grasses (Peterson et al., 2015; Soreng et al., 2017/2023).

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