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Genus Merremia in Family Convolvulaceae

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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Merremia (authority Dennst. ex Endl.) is a genus of climbing vines in the family Convolvulaceae, encompassing about 150 species worldwide (POWO, 2024). The plants occupy tropical and subtropical regions, with a pantropical distribution ranging from the Americas through Africa to Southeast Asia and the Pacific. The type species is Merremia hederacea (Burm.f.) Hallier f. (POWO, 2024).

Merremia species are perennial herbaceous or woody vines that twine, bearing leaves, often cordate and entire. Axillary inflorescences are cymose or solitary; flowers have a rotate funnel‑shaped corolla with five spreading lobes, usually pink or white, and a calyx of five free sepals. The superior ovary is bilocular, each locule with a single ovule. Fruits are schizocarps that split into mericarps containing winged seeds, aiding wind or water dispersal. A bracteole at the pedicel base, a short corolla tube, and a lack of a prominent perianth tube separate Merremia from Ipomoea (Stefanović & Austin, 2008).

Species richness peaks in tropical Africa and South America, with secondary centers in Southeast Asia and the Pacific. About 50 taxa are endemic to Madagascar and the Seychelles (WFO, 2024). Most species occupy open forest edges, scrub, savanna, or disturbed secondary growth from sea level to 1500 m; a few Andean taxa reach 2500 m (Miller & Humphreys, 2021). This pattern mirrors the historic dispersal routes of Convolvulaceae.

Pollination ranges from diurnal halictine bees to nocturnal sphingid moths, with flower colour and timing matching the pollinator guilds (Miller & Humphreys, 2021). Seeds are primarily wind‑dispersed, aided by mucilaginous coats that adhere to fur; some fruits are bird‑dispersed in understory habitats. Chromosome numbers reported for Merremia follow a polyploid series based on x = 15 (e.g., 2n = 30, 60, 90; Sharma et al., 2014).

Molecular phylogenies place Merremia in the tribe Merremieae and confirm its monophyly, although internal relationships remain unresolved (Stefanović & Austin, 2008). No formal subgeneric ranks have broad acceptance; informal species groups are used (Miller & Humphreys, 2021). Recent revisions have moved taxa formerly placed in Hewittia or Dichondra to Merremia, as recorded in WFO (2024).

Although not a major crop, a few Merremia species are grown as ornamental vines for their abundant flowers and vigorous growth. Conversely, several vines become invasive weeds in the United States and Africa, scrambling over crops and lowering yields (POWO, 2024).

Many narrow endemics face habitat loss, yet a comprehensive extinction‑risk assessment is lacking; targeted fieldwork is required to inform future conservation planning (WFO, 2024).

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