Resumen de Pollen morphology of the tribe Hemimerideae: Possible evidence of ancestral pollen types and parallel evolution in the basalmost clade of Scrophulariaceae s.str

Sergei L. Mosyakin, Zoya M. Tsymbalyuk

• Pollen morphology of nine species belonging to six genera of tribe Hemimerideae (representing the basalmost clade of Scrophulariaceae s.str.) was studied and illustrated with light microscopy (LM) and scanning electron microscopy (SEM). Pollen grains in Hemimerideae are 3- or 6–8-colpate or 3- or 5–8-colporate, prolate, spheroidal or oblate-spheroidal in shape; they are mainly medium-sized or occasionally small. The outline in polar view is 3-lobed, rounded-3-lobed or 5–8-lobed; the outline in equatorial view is elliptic or orbicular. Exine sculpture is rough, rough-foveolate, foveolate, microreticulate, rugulate, rugulate-foveolate or rugulate-microreticulate. Four major pollen types are recognized, based on original data: 3-colpate (Alonsoa), 6–8-colpate (Diclis, Hemimeris), 3-colporate (Colpias) and 5–8-colporate (Diascia, Nemesia). Within two of these pollen types, two subtypes can be further distinguished based on pollen size, exine sculpture, details of the colpi and endoapertures. Based on pollen morphological data presented here and in our previous studies combined with published molecular phylogenetic data and molecular clock estimates, we conclude that (1) the ancestral pollen type in Scrophulariaceae was 3-colporate with a rather “primitive” exine sculpture; (2) major trends and pathways of further morphological evolution of pollen among the all lineages of Scrophulariaceae were established at the early stages of diversification of the family, about the time of divergence of its main lineages; and (3) the signatures of parallel evolution of the main morphological pollen characters, combined with progressive diversification of exine sculpture patterns, are apparent in all major lineages of the family.