Systematic significance of tepal surface morphology in tribes Persicarieae and Polygoneae (Polygonaceae)

In order to improve understanding of the systematic relationships between taxa and of tepal-pollinator and tepal-habitat relationships, a detailed scanning electron microscopy (SEW study of the adaxial tepal surface of 135 taxa belonging to c. 14 genera in the tribes Persicarieae and Polygoneae (Polygonoideae-Polygonaceae) was carried out. The tepal surfaces have revealed some striking differences among the genera studied. Three main patterns of sculpturing and cell shape can be recognized. Type I: mostly rectangular to elongate cells with straight or undulating anticlinal walls; the cuticles smooth or striate in longitudinal direction and often continuous (Persicaria, Bistortu, Aconogonon, Koenigia and some species of Fagopyrum). Type II: irregular tesselated to elongated cells, rarely rectangular with mostly sinuate anticlinal walls; the cuticles rarely with longitudinal striation, but with strong orthogonal to reticulate ridges or striae, often without correlation between cells (Polygonum s.s., Polygonella, Fallopia, Parapteropyrum, Pteropyrum, Atraphaxis and Calligonum). Type III: mostly irregular, mammilliform, papillose cells with either longitudinal tightly pressed or randomly ridged cuticles (some species of Fagotyrum and Oxygonum). The present data generally support the division of Polygoneae and Persicarieae by Ronse Decraene & Akeroyd. The mammilliform, papillate epidermis of tepals in Oxygonum and some Fagopyrum is probably well-adapted to entomophily either as a foothold or even as a light-trap, and also shows some correlation with heterostyly. It is noteworthy that the tepal structure of Polygonella (tesselated form) is highly similar to that of Polygonum s. s. (especially P. sect. Duravia). Cuticular striation alone does not appear to have much systematic value, but has a mechanical function in affording extra strength to the cell walls. Some correlations between the degree/shape of cuticles and the pollination mechanisms or the habitat of each taxon are also briefly discussed. It is concluded that the studied tepal characters can be useful in improving the classification of tribes Persicarieae and Polygoneae, arid give additional support at the infrageneric level.