Pollen morphology and taxonomy of Atraphaxis (Polygoneae,Polygonaceae)

Pollen grains of 32 species of Atraphaxis L. including six species previously attributed to Polygonum L. s.str. were investigated with LM (acetolysed pollen) and SEM (dry pollen). Pollen grains of all studied species are spheroidal to oblong-spheroidal, mostly tricolporate, rarely 4-6-loxocolporate, ellipsoidal in equatorial view, rounded-trilobed or trilobed in polar view, with striate or striato-perforate, reticulato-foveolate, or reticulato-perforate sporoderm ornamentation. Exine sculpture is the most variable feature, differing in width, distinctness, and spacing of the striae, which are divided by grooves with small pits or perforations in rows. The most distinct variants of sporoderm ornamentation are connected by a full range of transitions. Striato-perforate ornamentation is common in species with the perianth typical for Atraphaxis, whereas reticulato-foveolate or reticulato-perforate sporoderm ornamentation was found in species with the perianth of Polygonum-type.