More Problems Despite Bigger Flowers: Systematics of Cuscuta tinctoria Clade (subgenus Grammica, Convolvulaceae) with Description of Six New Species

Cuscuta tinctoria clade, the second largest infrageneric group of subgenus Grammica, includes 14 species that are centered in Mexico and adjacent regions, but also two species that are found in Australia, presumably as a result of long-distance dispersal. Flowers, pollen, and stigmas are among the largest in Cuscuta, with plants being xenogamous or facultatively xenogamous. In this clade, the convergent evolution of morphological traits, especially those associated with the calyx and gynoecium/capsule, has obscured the identity of some species and has hindered previous efforts to determine their limits. Basic morphology, scanning electron microscopy and sequence data from the nuclear internal transcribed spacer (ITS) and the plastid trnL-F region were used to reconstruct the phylogeny, gain a better understanding of the evolutionary history, and determine species boundaries. Overall, species were grouped in five subclades. Based on their morphological and molecular similarity, C. tinctoria, C. aurea, and C. floribunda are best treated as a single species, with the latter two taxa being retained as varieties of the former. Our results also show that in their currently accepted delimitation, C. rugosiceps and C. tinctoria are polyphyletic, the former including one new species, C. volcanica, and the latter two new species, C. timida and C. tolteca. In addition, three other new species are described: C. iguanella and C. insolita, both with multicellular protuberances on the calyx and/or corolla lobes, and C. montana, with broader than long calyx lobes. A taxonomic treatment that includes an identification key, descriptions, geographical distribution, ecological data, and illustrations for all taxa is provided.