NEW SPECIES, NEW COMBINATIONS, AND NEW RECORDS IN CONVOLVULACEAE FOR THE FLORA OF THAILAND
In 2005 I had the opportunity to study the original material belonging to J.D. Choisy that he used to prepare the Convolvulaceae Orientale (Choisy 1834, 1837); the specimens bearing Choisy’s autograph names are mostly now conserved in the De Candolle Herbarium at Geneva (G-DC), Choisy having donated his personal herbarium to Augustin Pyramus de Candolle when the latter was amassing what became the Prodromus Herbarium. Choisy had acquired a very complete set of the Convolvulaceae specimens from the East Indian Company’s herbarium after a visit to London ca 1830, at which time Nathaniel Wallich was working on the Numerical List (Wallich 1828–1849) that is usually referred to simply as the “Wallich Catalogue” and preparing to distribute sets of duplicates. Choisy may well have studied all the specimens in the East India Company herbarium during his visit and a comprehensive set of the Convolvulaceae was either given to him then, or sent to Geneva soon thereafter. These East India Company (or “Wallich”) specimens formed the foundation for the Convolvulaceae Orientale, and many of the specimens became the types for Choisy’s new species.
Of particular relevance in this case is the type material for Choisy’s Calonyction asperum, based on a De Silva specimen made in Sillet (now Sylhet, in Bangladesh). The specimens in G-DC occupy three sheets and the material is an excellent match with the Thai specimens I previously called I. trichosperma. The following nomenclatural summary sets out the relevant synonymy, and detailed discussion follows.
Ipomoea aspera (Choisy)Vatke, Linnaea 43: 508. 1880–82, as to type but not as to specimens cited.— Calonyction asperum Choisy,Me´m. Soc. Phys. Geneve 6: 442. [Conv. Or. 60] 1834. Type: [Bangladesh] Sillet, F. de Silva sub Wallich Cat. 1388 (3 sheets, G-DC!).— Misapplied: I. trichosperma sensu authors: Staples et al. 179. 2005; Gagnep. & Courchet in H.Lecomte, Fl. Indo-Chine 4: 287. 1915; non Blume, Bijdr. 13: 710. 1824.
Choisy (1834) based C. asperum solely on the de Silva collection from Bangladesh but later (Choisy 1845) cited an additional specimen collected by Bojer from the Comoros that he thought was conspecific; the latter is not type material for the name and coincidentally is a specimen of I. violacea L., the beach moonflower. Clarke (1883) reduced C. asperum to synonymy with I. grandiflora (= I. violacea) without comment; the name has not been used in Asia since. Vatke (1882) in combining the epithet asperum in Ipomoea, did so without having seen the type, but instead compared a Madagascan specimen with a duplicate of Bojer’s Comoros material. In this way, the name I. aspera came to be associated with a plant from the African region rather than an Asian one; as an aside, I. aspera is not dealt with in the recent Madagascan flora account (Deroin 2001) nor is it mentioned in twentieth century floras for the Indian subcontinent: Bangladesh (Khan 1985); Assam (Clarke 1939); Bhutan (Mill 1999); nor for Indochina (Gagnepain & Courchet 1915).
Further research, including study of all relevant type material, may prove that I. aspera is conspecific with the Malesian I. trichosperma, but the type specimen for that name has been missing for a long time (Van Ooststroom 1940: 579, in footnote) and remains so today (G. Thijsse, pers. comm. 2007). Resolution of this matter must await revisionary study of the Asian moonflower complex. For the time being, the pragmatic course is to take up the name I. aspera for the continental Asian moonflower species with markedly unequal sepals, giving the Thai plants an unambiguous name.