Xyloselinum laoticum (Umbelliferae), a new species from Laos, and taxonomic placement of the genus in the light of nrDNA ITS sequence analysis

摘要

A new species of Xyloselinum, X. laoticum, endemic to the Vientiane province of Laos, is described and illustrated. Similar to two previously described species of Xyloselinum from limestone ridges of Northern Vietnam, the new species is subshrub with 2-3 pinnatisect leaves having petiolulate basal segments and broadly lanceolate terminal segments, solitary or binary mericarp vallecular vittae, almost flat on the commissural side endosperm. The new species is more closer to X. vietnamense than to X. leonidii. Xyloselinum laoticum differs from X. vietnamense in irregularly toothed or laciniate terminal leaf segments without bladders on lower surface, solid (not fistulose) petioles, globose umbels and umbellets, almost glabrous (not densely covered by scattered short prickles) pedicels, always entire bracteoles, and conical (not shortly conical) stylopods. It is supported by the nrDNA ITS data that Xyloselinum is treated as an independent genus and placed in Selineae Clade together with some S and E Asian genera separated from Peucedanum s.l. or Ligusticum/Selinum complex.