Reproductive morphology of the genus Pentactina (Rosaceae) and systematic implications

This study aimed to investigate the reproductive morphological characteristics of the genus Pentactina, which comprises two species, in order to identify previously unstudied characteristics and elucidate their systematic implications within the tribe Spiraeeae. Floral elements and ovule characters were studied using microtome sections, and seed surface patterns were analyzed via scanning electron microscopy. The results indicated that P. rupicola and P. schlothauerae shared identical reproductive morphological characteristics, including the dicotyledonous type of anther wall formation, tetrasporangiate anthers, a glandular tapetum, simultaneous cytokinesis, two-celled mature pollen at shedding time, anatropous and unitegmic ovules, two ovules per carpel, the development of the nucellar cap, a thin endosperm, a rectangular-reticulate seed surface sculpture pattern, and an endotestal type of seed coat. In conclusion, no distinct reproductive morphological differences were observed between the two species of Pentactina. Although Pentactina and Spiraea exhibit similar external morphological characters, they can be taxonomically differentiated based on reproductive morphological characteristics such as the number of ovules per carpel and the seed surface sculpturing pattern. These two reproductive morphological characteristics provide strong evidence supporting the transfer of Spiraea schlothauerae to the genus Pentactina. Therefore, the results of this study do not support Hutchinson’s and Kalkman’s taxonomic treatments as a synonym of Spiraea.