Pollen morphology of Persicaria section Cephalophilon (Polygonaceae)

Pollen morphology of 19 taxa in Persicaria section Cephalophilon and four related taxa in the genus Koenigia was examined. Pollen grains shed as a monad were oblate to subprolate in shape (P/E = 0.50–1.20), small to large in size (13.44–51.16 μm), and tricolpate, octocolpate, or pantoporate. Three types of exine ornamentation were identified: (I) reticulate ( P . sect. Cephalophilon ), (II) reticulate with microechinae ( Koenigia delicatula ), and (III) microechinate (studied taxa of Koenigia except K. delicatula ). The quantitative pollen characteristics analyzed using principal component analysis showed diagnostic importance among the taxa. The comprehensive consideration of pollen characteristics (aperture type, pollen size, and detailed exine ornamentation) is systematically informative, particularly at the series level of P. sect. Cephalophilon . Furthermore, the results also support the separation of some taxa of uncertain taxonomic affinities between Koenigia and P . sect. Cephalophilon . Orbicules were absent in all taxa of P. sect. Cephalophilon but were consistently found in Koenigia. The examined orbicules were spherical with a psilate surface, and the studied orbicule characteristics provided additional evidence to clarify the taxonomic position of some taxa of Koenigia. The orbicule and pollen morphology, especially aperture types, has proven to be a useful diagnostic characteristic in P. sect. Cephalophilon and related taxa, and their systematic importance is further discussed in this study.