A study on fruit morphology of Polygonum sect. Polygonum (Polygonaceae) from China

Abstract

The morphology of fruits in 16 species, one variety and one form of Polygonum sect. Polygonum from China was studied under stereoscope and scanning electron microscope (SEM). Fruits were observed heterocarpic in five species of the annuals of Polygonum sect. Polygonum, viz., shorter fruits (shorter or sub-equal to persistent perianths) vs. longer fruits (obviously longer than persistent perianths). Based on morphology of achene surface, fruits of Polygonum sect. Polygonum can be divided into two types: (1) achenes smooth and shiny, but not tuberculate or verrucate; (2) achenes scabrous, but not or slightly shiny, tuberculate or verrucate. The first type includes two subtypes: (1) achenes shallowly waved, e.g., P. cognatum, P. argyrocoleum and P. acerosum; (2) achenes with irregular hollows or stellate plications, e.g., P. plebeium, P. polycnemoides and P. shiheziense. The second type includes four subtypes: (1) achenes irregularly verrucate, e.g., P. intramongolicum; (2) achenes with scattered tubercules, e.g., P. humifusum and the shorter fruits of P. patulum; (3) achenes with tubercules standing in a queue, e.g., P. aviculare, P. tachengense and shorter fruits of P. urumqiense; (4) achenes with tubercules scattered in upper part and hollows or stellate plications in lower part, e.g., the longer fruits of P. aviculare, P. aviculare f. erectum, P. patulum and P. rigidum. The heterocarpy and micro-morphological characteristics of fruits are valuable to identify species and varieties in Section Polygonum. In this study, the systematic position of Polygonum aviculare L. var. fusco-ochreatum (Kom.) A. J. Li was determined and restated as Polygonum fusco-ochreatum Kom. and a new species, Polygonum huichunense F. Z. Li, Y. T. Hou C. Y. Qu, was described.