Cuscuta alata

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 : 379-380

Cuscuta alata is a “good” species

Cuscuta alata described by Brandegee (1909) from Sinaloa was considered by Yuncker (1921) a “strongly keeled form” of C. applanata and the author considered the two names likely trees (ITS). Closely related C. americana and C. victoriana are used as outgroups. Branch lengths are drawn at the same scale for all three phylograms. ML bootstrap values are indicated for nodes supported ≥ 50%. Numbers following species names correspond to DNA accessions (see Appendix 2)

synonymous, which is how C. alata has been viewed since. Although it shares some morphological similarities with C. chinensis (incl. var. applanata ), C. alata is the most dissimilar species of this clade both from a molecular and morphological point of view ( Figs. 1 , 2 , 3 ). Multicellular projections in the form of crests or wings develop on the keels of both the calyx and the corolla lobes ( Figs. 1 , 2 ). In addition, the corolla lobes in C. alata are lanceolate and acute to acuminate, while in C. chinensis they are ovate and obtuse to rounded. More remarkably, flowers of C. alata often develop small external infrastaminal scales with 1–2 fimbriae on the dorsal part of the corolla tube, below the sinuses of the corolla lobes ( Fig. 2h–i ). In view of these findings, C. alata is reinstated as a species.

The former Cuscuta potosina includes two species

Cuscuta potosina var. globifera and C. yucatana formed a well-supported clade in the C. chinensis species complex, while C. potosina ( var. potosina ) was part of the sister clade that included both varieties of C. chinensis ( Fig. 3 ). Cuscuta potosina var. globifera is also clearly distinct morphologically from C. potosina ( var. potosina ), C. chinensis , and C. yucatana (see identification key and descriptions below). Consequently, C. potosina var. globifera is described as a new species, C. azteca . Cuscuta globifera W.Schaffn. ex Yunck. is an invalid name, and we preferred to avoid a new combination based on the basyonim of var. globifera Yunck. because several other very similar species epithets are already in use (e.g., C. globosa Ridl. ; C. globulosa Benth. , C. globiflora Engelm. ).

Cuscuta potosina ( var. potosina ) was similar to C. chinensis var. applanata from a molecular point of view. However, it stands apart in this complex of species through its 4-merous flowers and 1-seeded capsules (see the identification key and descriptions). In this latter case, we considered appropriate to maintain C. potosina as a species based on its morphological distinction.

Figures

Fig. 1 a–i Morphology of dissected calyx in species of Cuscuta chinensis complex. a,d Cuscuta chinensis var. chinensis. b,e C. chinensis var. applanata. c,f C. alata. g C. potosina. h C. azteca. i C. yucatana. Bars 1 mm

Fig. 2 a–g Scanning electron micrographs of multicellular protuberances on the calyx of Cuscuta chinensis species complex. a C. chinensis var. chinensis. b C. chinensis var. applanata. c–e C. alata. f

Fig. 3 Phylogenetic relationships among species of the Cuscuta chinensis (C. c.) complex obtained from maximum likelihood (ML) analyses of individual trnL-F (a) and ITS (b) as well as combined datasets (c), all under the HKY + G model of DNA evolution. Asterisks indicate nodes that collapsed in a strict consensus of equally