Melica

Melica is a genus of perennial grasses known generally as melic or melic grass. They are found in most temperate regions of the world.^[1]

Melic grasses are clumping to short-rhizomatous grasses. They have flowering culms up to 250 cm (98 in) tall bearing spikelets of papery flowers. The spikelets have between one and seven fertile flowers with a rudimentary structure at the distal end composed of one to four sterile florets.^[1] Some species of melic have corms, lending them the name oniongrass.^[2]

The genus is most diverse in South America and temperate Asia.^[3] Eight species are endemic to China.^[4] In North America, most species occur west of the Mississippi River, with exceptions being Melica mutica and M. nitens which occur throughout much of the southeast and lower Midwest respectively.^[1][5]

Recent molecular phylogenetic studies have confirmed that Melica is a monophyletic genus, meaning that all species share a common evolutionary origin.^[6] These studies indicate that earlier classifications based primarily on morphology do not fully reflect evolutionary relationships within the genus.^[6]

Species and hybrids include:^[3][7]

Molecular phylogenetic analyses based on nuclear (ITS, ETS) and plastid (trnL–F) DNA sequences have resolved Melica into eight major clades corresponding to infrageneric sections:^[6]

• Melica sect. Melica
• sect. Agonomelica
• sect. Bromelica
• sect. Cupani
• sect. Dalycum
• sect. Melicella
• sect. Melicula
• sect. Uniflorae

The species Melica uniflora is identified as the earliest-diverging lineage within the genus.^[6] Phylogenetic evidence also supports the inclusion of previously segregated genera such as Bromelica within Melica.^[6]

Species of Melica are characterized by relatively uniform chromosome numbers. Most species are diploid with a chromosome number of 2n = 18 and a basic chromosome number of x = 9.^[6] Polyploidy occurs in some taxa but is comparatively rare within the genus.

Genome size studies indicate that Melica species possess small genomes with moderate but significant variation among phylogenetic lineages.^[6] Genome sizes are generally stable within species but differ between sections, suggesting that gradual changes in DNA content have contributed to diversification.

Compared to related genera such as Glyceria and Schizachne, Melica exhibits higher DNA content and a reduced basic chromosome number, indicating that major genomic changes likely occurred early in the evolution of the genus.^[6]

Phylogenetic and distributional evidence suggests that Melica likely originated in Europe to western Asia, where early-diverging lineages such as Melica uniflora are found.^[6]

The genus exhibits geographically structured lineages, including Eurasian groups distributed across Europe, the Mediterranean, and eastern Asia, a North American lineage corresponding largely to sect. Bromelica, and a South American lineage corresponding to sect. Melicula.^[6] These patterns are consistent with regional diversification and historical long-distance dispersal events.^[6]