Taxonomic relevance of pollen characteristics for several Ranunculus (section Batrachium , Ranunculaceae) species from western Siberia

The present study addresses the pollen characteristics of five species and 16 populations of the genus Ranunculus section Batrachium – Ranunculus subrigidus W. B. Drew, Ranunculus circinatus Sibth., Ranunculus trichophyllus Chaix, Ranunculus kauffmannii P. Clerc, and Ranunculus mongolicus (Krylov) Serg. – from different water bodies of western Siberia. Light microscopy (LM) and scanning electron microscopy (SEM) were used to obtain data on pollen fertility, shape, size parameters, and exine thickness and ornamentation. In addition, phylogenetic relationships between the investigated taxa including potential hybrids were estimated using the internal transcribed spacer (ITS) of the 35S nuclear ribosomal DNA region. LM showed that rehydrated pollen grains of all the species excluding R. kauffmannii were mostly fertile, spheroidal, tricolpate, and medium sized (∼30–36 μm). Pollen of R. kauffmannii had a lower percentage of spheroidal fertile grains, which were significantly (p < 0.0001) larger (44.29 ± 6.07 μm) than grains of other species. SEM showed that dry pollen grains mostly changed their shape to subprolate, prolate or some asymmetrical classes and considerably changed their size parameters due to the harmomegathic effect. The proportions of different shape classes of dry grains varied between populations and species. The exine had a microechinate ornamentation and a thickness of ∼0.5 μm. The complex of pollen characteristics can provide valuable information for taxonomic and evolutionary studies of Ranunculus section Batrachium.