Annals of the Missouri Botanical Garden vol:91 issue:2 pages:320-345
A comparative morphological study of floral characters of the North American genus Polygonella and the four currently accepted sections of Polygonum s. str. (sect. Polygonum, sect. Duravia, sect. Pseudomollia, sect. Tephis) has been carried out with light microscopy (LM) and scanning electron microscopy (SEM). Flowers were investigated for macromorphological characters, tepal epidermal characters, pollen, and fruit morphology and anatomy. Results demonstrate that the limits between both genera become blurred through section Duravia of Polygonum, especially in characters of pollen and fruit morphology. Polygonum sect. Duravia and Polygonella share a wealth of intergrading floral and vegetative characters at the macroscopic, as well as ultrastructural, level (pollen morphology, fruit morphology, flower structure, vegetative anatomy). These characteristics, especially the pollen morphology, are sharply delimited from section Polygonum. Evidence presented here allows for a broader concept of Polygonum s. str. to be adopted, with an extended section Duravia including subsections Duravia and Polygonella. A cladistic analysis of morphological characters supports two distinct clades, section Polygonum with subsections Polygonum and Tephis, and section Duravia with subsections Duravia and Polygonella.