CONVOLVULACEAE

CONVOLVULACEAE View in CoL

New combinations in Convolvulus needed to treat Calystegia species Primary author:Alan S. Weakley

All evidence suggests that Calystegia is phylogenetically embedded in Convolvulus (Stefanovic´ et al. 2003;

Williams et al. 2014; Wood et al. 2015; Mitchell et al. 2016). To render monophyletic genera in tribe

Convolvuleae , either Calystegia should be subsumed into Convolvulus (and perhaps given section rank) or,

alternatively, Convolvulus could be split into multiple monophyletic genera corresponding to major clades,

with Calystegia then retaining genus rank as one of those clades. There seems to be no interest in following the

alternative of splitting Convolvulus , and indeed, segregate genera would be difficult to diagnose morphologi-

cally. In their “foundation monograph of Convolvulus ,” Wood et al. (2015) stated that “ Calystegia may be dis-

tinguished from Convolvulus by its pollen (polypantoaperturate versus equatorially triaperturate), stigmas

(globose versus linear/clavate) and bracteoles that are large and inflated and enclose the calyx in Calystegia

whereas in Convolvulus they are typically small and often remote, large bracteoles only occurring in

Convolvulus scammonia and C. pseudoscammonia .” They went on to state that:

Thus, Calystegia is a clearly defined subgroup within Convolvulus that has been treated at a more or less

global-level by a single author [Brummitt]. For these reasons we decided to pursue a pragmatic approach

excluding Calystegia from this monograph of C onvolvulus. For those who would consider all taxonomy

should be based on monophyletic taxa, this issue is readily resolved by re-naming all species of Calystegia

as Convolvulus . The necessary combinations are already available for most of the taxa concerned.

We take this to indicate that Wood et al. (2015) “pragmatically” exclude Calystegia from their monograph of Convolvulus (considering its taxonomy relatively resolved by Brummitt and not wanting to reopen it in the context of the rest of Convolvulus ), not from the genus. The phylogenetic tree in Mitchell et al. (2016) suggests that Calystegia is indeed monophyletic but is part of a slightly larger clade with Convolvulus pseudoscammonia K. Koch , Convolvulus chinensis Ker Gawl. , and Convolvulus scammonia L. successively sister to Calystegia , suggesting that the few morphological characters used to recognize Calystegia accrued successively, complicating and obscuring the circumscription of and morphological basis for maintaining Calystegia at any rank.

For use in the Flora of the Southeastern United States, we therefore make necessary combinations to treat species often placed in Calystegia as members of Convolvulus . Brummitt’s (1965, 1980, 2023) taxonomic approach in Calystegia was to employ many trinomials, grouping subspecies which he considered to be related within an umbrella species. Some of these subspecies are sharply delineated from one another morphologically or represent different lineages on separate continents—e g, Calystegia silvatica (Kit.) Griseb. ssp. silvatica in Europe and Calystegia silvatica ssp. fraterniflorus (Mack. & Bush) Brummitt in North America. Other subspecies show some degree of (apparent) hybridization, intermediacy, or at least nondeterminability of herbarium specimens, both between the subspecies of a species and between the subspecies of one species and those of a different species. As a community, we lack molecular sampling at enough depth (either in samples per taxon or in sequences per sample) to make detailed hypotheses about the relationships of the consensus taxa recognized by Brummitt and others (primarily as subspecies). We therefore judge that the taxonomy established here will be more stable by being “flatter,” with the taxa all accorded species rank, without a premature attempt to imply degrees of relationship with a trinomial taxonomic system.