The variation of perforation plates of vessels in the secondary xylem of Euptelea pleiosperma (Eupteleaceae)

Abstract

The systematic position of the Eupteleaceae, a monogeneric family including only two species (Euptelea polyandra and E. pleiosperma) and endemic to East Asia, has long been in dispute. This paper deals with the variation of the vessel perforation plates of the secondary xylem of the stem of E. pleiosperma in order to provide new anatomical evidence for a better understanding of the systematic position of this family. The results showed that there were two types of vessels in the secondary xylem of the stem of the species, the tracheid-like vessels and typical vessels. In the tracheid-like vessels, the perforation pits were larger than those in the lateral wall, arranged irregularly and did not exhibit typical morphological features of perforation plates, and the membrane of the perforation pits disappeared completely or partly. In the typical vessels, the perforation plates were of varying forms, falling into several subtypes: reticulate perforation plates (including the foraminate ones); reticulate-scalariform perforation plates in which the perforation pits were both reticulate and scalariform; scalariform perforation plates in which scalariform multi-perforation plates were often observed; the transitional form from scalariform perforation plates to simple perforation ones; and some other forms of perforation plates which could not be referred to any subtypes mentioned above. The membrane remnants could be observed only in the perforation pits of the scalariform perforation plates. Multiple end wall and lateral-wall perforation plates were also observed in the secondary xylem. Based on the present results and a comparison between the perforation plate types in the Eupteleaceae with those of the other members of Ranunculales, we considered that the Eupteleaceae might occupy a basal position in the order. We also inferred that the formation of the perforation plates in E. pleiosperma may have undergone different pathways.