领春木茎次生木质部中导管穿孔板的变异

领春木Euptelea pleiosperma Hook. f. &; Thoms.隶属领春木科Eupteleaceae。该科为东亚特有的单型科,其系统位置一直颇有争议。本文对中国产领春木茎次生木质部中导管穿孔板的变异进行了观察,以期为它的系统位置提供进一步的解剖学证据。结果表明,领春木茎次生木质部中包括无明显穿孔板的管胞状导管和典型的导管两种类型。在无明显穿孔板的导管中,穿孔中的纹孔膜全部或部分消失,但穿孔无规则排列或聚集,不形成具典型的形态特征的穿孔板;在典型的导管中,穿孔板形态变异较大,包括几个类型:网状穿孔板(含麻黄式穿孔板)、网状和梯状混合型穿孔板、梯状穿孔板、梯状穿孔板向单穿孔板的过渡。在上述导管穿孔板类型中,只有梯状穿孔板的穿孔中可以观察到纹孔膜的残余。在领春木次生木质部中也观察到了端壁多穿孔板及侧壁穿孔板。根据观察结果,我们认为领春木次生木质部导管穿孔板的许多特征说明该科可能处于毛茛目中比较原始的系统位置。

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

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.