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Genus Decalepis in Tribe Periploceae

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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Decalepis is a small genus in Asclepiadoideae (Apocynaceae), with an established type as Decalepis hamiltonii (Wight & Arn.). It comprises perennial, twining lianas bearing milky latex, distributed across peninsular India, with the principal center of diversity and endemism in the Western Ghats and a smaller set of taxa in the Eastern Ghats and adjacent interior (POWO, 2024; Meve & Liede, 2010; Liede & Meve, 2022). The plants typically carry opposite leaves with prominent interpetiolar or axillary pseudo-stipules that in several species fuse to form a pocket-like structure, a distinctive feature supporting recognition of the genus (Meve & Liede, 2010; Liede & Meve, 2022). Inflorescences are lax, axillary or subterminal cymes bearing relatively small, rotate corollas with an annular, corolline corona; the stamens are inserted at the base of the corolla tube and the anthers bear an apical appendage, while the style-head is capitate and the gynostegium bears an exserted translator apparatus adapted for insect pollination (Meve & Liede, 2010). Fruits are paired follicles, a synapomorphy of Asclepiadoideae, and seed comas are well developed (Liede & Meve, 2022). Developmentally, individuals grow as long-lived perennials that resprout seasonally and colonize support structures such as shrubs, small trees, and rock faces; chromosome counts reported from Indian material are often x = 11, though variation has been noted and the number is best treated as provisional (Meve & Liede, 2010; Liede & Meve, 2022).

Within Marsdenieae, Decalepis has been resolved as closely related to Vincetoxicum sensu lato, but relationships to genera such as Cynanchum and Marsdenia are nuanced and the exact placement of Decalepis varies with sampling and molecular locus choice; sectional or subgeneric rankings have been proposed historically, and several species originally described in Marsdenia have been transferred to Decalepis, a re-circumscription widely adopted by major checklists (Meve & Liede, 2010; Liede & Meve, 2022; POWO, 2024). Alternative treatments, including maintenance of some taxa in Marsdenia or expansion of Vincetoxicum to accommodate former Decalepis species, continue to appear in regional accounts, reflecting ongoing reconciliation of morphological and molecular data and underscoring the need for thorough multi-locus studies and comprehensive taxonomic revisions (POWO, 2024; Liede & Meve, 2022).

The genus holds horticultural and ethnobotanical importance in the Indian subcontinent, where D. hamiltonii is a highly valued root known in trade and occasionally cultivated or wild-harvested, while other species are cultivated locally; impacts on native plant communities from targeted collection are not quantified but provide a practical concern. Conservation status remains uncertain; assessments are scattered and sometimes divergent, and targeted surveys of known populations, including those within protected areas of the Western Ghats, are prioritized to better quantify threats, particularly overharvesting and habitat loss. Ongoing phylogenetic and taxonomic work integrating molecular, morphological, and ecological data is expected to clarify circumscription, relationships, and conservation priorities across the genus (Meve & Liede, 2010; Liede & Meve, 2022; GBIF, 2024).

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