Spermacoce in the Americas: small group, small flowers but great taxonomic problems

SALAS, R.M.; SOBRADO, S.V.; CABAÑA, F.A.A.; FLORENTÍN, J.E.; MIGUEL, L.M.; JANSSENS, S.; DESSEIN, S.; CABRAL E.L.

Copenhagen

Conferencia; VII International Rubiaceae and Gentianales Conference; 2017

Natural History Museum of Denmark

The genus Spermacoce belongs to tribe Spermacoceae s.l. Together with 23 other genera itforms the monophyletic Spermacoce clade. Several genera of this Spermacoce clade are well supported by molecular data (e.g. Mitracarpus, Richardia, Galianthe), while others areparaphyletic (e.g. Borreria and Spermacoce). The generic boundaries of Spermacoce areproblematic and currently strongly discussed. There are two concepts, the most comprehensive one includes other genera (Borreria and parts of Diodia), whereas the narrow one includes only the type S. tenuior, and seven closely related species. Based on our molecular dataset (ITS and ETS), the genus comprises American and Australian species divided into three lineages: Spermacoce s.s. (including type species), S. eryngioides group (ex B. sect. Pseudodiodia), and an Australian group. In the Americas, Spermacoce differs from its closest relatives in having small urceolate corolla, lobes internally pilose, stamens and stigma included, and pollen grains with tectate exine, long colpi, and endocingulum. In this continent, as defined above, it comprises 35 species, of which five are new to science. The review, based on over 1900 specimens, provides nomenclatural and taxonomic discussion about the type species, the S. ocymoides complex, and the geographic distributions. Species within Spermacoce can be distinguished from each other based on calyx lobes/corolla length ratio, internal indumentum of the corolla, morphology of the ventral face of the seeds, exotesta patterns, and pollen characters such as shape, number of colpi, distribution of perforations, and supratectal elements.