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

SALAS, R. M.; SOBRADO, S. V.; FADER, ANDREA ALEJANDRA CABAÑA; FLORENTÍN, J. E.; MIGUEL, L. M.; JANSSENS, STEVEN; DESSEIN, STEVEN; CABRAL, E. L.

Congreso; VII International Rubiaceae and Gentianales Conference; 2017

ThegenusSpermacoce belongstotribeSpermacoceaes.l.Togetherwith23othergeneraitformsthemonophyleticSpermacoce clade.SeveralgeneraofthisSpermacoce cladearewellsupported 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 mostcomprehensiveoneincludesothergenera(Borreria andpartsofDiodia),whereasthenarrowone includes only the type S. tenuior, and seven closely related species. Based on ourmoleculardataset(ITSandETS),thegenuscomprisesAmericanandAustralianspeciesdividedintothreelineages:Spermacoce s.s.(includingtypespecies),S.eryngioides group(exB. sect.Pseudodiodia),andanAustraliangroup.IntheAmericas,Spermacocediffersfromitsclosestrelatives in having small urceolate corolla, lobes internally pilose, stamens and stigmaincluded,andpollengrainswithtectateexine,longcolpi,andendocingulum.Inthiscontinent,asdefinedabove,itcomprises35species,ofwhichfivearenewtoscience.Thereview,basedonover1900specimens,providesnomenclaturalandtaxonomicdiscussionaboutthetypespecies, the S. ocymoides complex, and the geographic distributions. Species withinSpermacoce canbedistinguishedfromeachotherbasedoncalyxlobes/corollalengthratio,internalindumentumof thecorolla,morphologyof theventral face of theseeds,exotestapatterns,andpollencharacterssuchasshape,numberofcolpi,distributionofperforations,andsupratectalelements