Cuscuta yucatana

Stefanović, Mihai Costea Ian Spence Saša, 2011, Systematics of Cuscuta chinensis species complex (subgenus Grammica, Convolvulaceae): evidence for long-distance dispersal and one new species, Organisms Diversity & Evolution (New York, N. Y.) 11 (5), pp. 373-386 : 380

Cuscuta yucatana and C. acuta : convergent or reticulate evolution?

Cuscuta yucatana not only exhibits the same type of umbelliform inflorescence that characterizes the C. umbellata species complex (“clade L”, Costea and Stefanović 2010), but it also resembles morphologically C. acuta —a species that belongs to the latter clade and grows in the Galapagos Islands and the Pacific coast of Ecuador and Peru. Both species have indehiscent fruit in clades with dehiscent (or preponderantly dehiscent) capsules. The similarity between the two species was also noted by Yuncker (1935), who included C. yucatana in the same subsection as C. acuta (subsect. Acutae) and differentiated the former species by the smaller flowers, longer pedicels, and obovoid shape of its capsules. Homoplasy is observed for many morphological characters in Cuscuta ; for example, fruit indehiscence ( Stefanović et al. 2007), pollen features ( Welsh et al. 2010), and numerous gynoecium characters ( Wright et al. 2011). Species from different clades of subg. Grammica may share some elements of morphology (e.g., the same type of inflorescence, flower parts or capsule). Unfortunately, too little is known about the ecology and host range of the two species to attempt a biological explanation of convergent evolution. One common ecological factor may be the halophytic habitat— coastal ( C. acuta ) or mainland ( C. yucatana )—that these species apparently inhabit. Alternatively, the morphological similarity between C. acuta and C. yucatana may be explained through putative hybridization involving species from both clades. The evolutionary history of the C. umbellata clade has been marked by extensive reticulation among its members ( Costea and Stefanović 2010), and hybridization involving the C. chinensis complex and species from another major clade of subg. Grammica (“clade B”) have also been documented ( Stefanović and Costea 2008). Although reticulation involving species from C. chinensis and C. umbellata clades was not been detected with the molecular markers used in this study, it may be revealed in the future by low-copy nuclear genes ( Stefanović and Costea 2008).