SYSTEMATIC SIGNIFICANCE OF TEPAL SURFACE-MORPHOLOGY IN TRIBES PERSICARIEAE AND POLYGONEAE (POLYGONACEAE)

In order to improve understanding of the systematic relationships betw een taxa and of tepal-pollinator and tepal-habitat relationships, a de tailed scanning electron microscopy (SEM) study of the adaxial tepal s urface of 135 taxa belonging to c. 14 genera in the tribes Persicariea e and Polygoneae (Polygonoideae-Polygonaceae) was carried out. The tep al surfaces have revealed some striking differences among the genera s tudied. Three main patterns of sculpturing and cell shape can be recog nized. Type I: mostly rectangular to elongate cells with straight or u ndulating anticlinal walls; the cuticles smooth or striate in longitud inal direction and often continuous (Persicaria, Bistorta, Aconogonon, Koenigia and some species of Fagopyrum). Type II: irregular tesselate d to elongated cells, rarely rectangular with mostly sinuate anticlina l walls; the cuticles rarely with longitudinal striation, but with str ong orthogonal to reticulate ridges or striae, often without correlati on between cells (Polygonum s.s., Polygonella, Fallopia, Parapteropyru m, Pteropyrum, Atraphaxis and Calligonum). Type III: mostly irregular, mammilliform, papillose cells with either longitudinal tightly presse d or randomly ridged cuticles (some species of Fagopyrum and Oxygonum) . The present data generally support the division of Polygoneae and Pe rsicarieae by Ronse Decraene & Akeroyd. The mammilliform, papillate ep idermis of tepals in Oxygonum and some Fagopyrum is probably well-adap ted to entomophily either as a foothold or even as a light-trap, and a lso 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 stria tion alone does not appear to have much systematic value, but has a me chanical 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 impro ving the classification of tribes Persicarieae and Polygoneae, and giv e additional support at the infrageneric level. (C) 1998 The Linnean S ociety of London.