科研之友
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摘要
The wood and bark structure of the distinctive southern African genera Polemanniopsis (including the newly described species P. namibensis) and Steganotaenia have been described. To allow for comparisons with the traditional subfamily Saniculoideae, a shrubby species of Eryngium from the Juan Fernandez Islands was also studied. Polemanniopsis and Steganotaenia were recently considered as two closely related genera forming a new tribe Steganotaenieae of subfamily Saniculoideae (Apiaceae), whereas Eryngium is commonly recognized as a member of Saniculoideae. Eryngium differs significantly from the other two genera in the smaller size of intervessel pits, sclerification and radial dilatation in collapsed secondary phloem, the absence of crystals in the phelloderm cells and the occurrence of druse crystals in secondary phloem ray cells. Steganotaenia and Polemanniopsis share features, including the presence of marginal axial parenchyma, the occurrence of radial secretory canals in secondary xylem, dilatation of the secondary phloem by axial parenchyma stretching, cortical periderm initiation and the presence of chambered phelloderm cells containing druse crystals. These characters (especially the occurrence of chambered crystalliferous cells in phelloderm, which has not yet been reported for Apiaceae) support both the monophyly and the isolated position of the Steganotaeniae. No reliable synapomorphic features could be found to support a relationship with Saniculoideae. Steganotaenia is remarkable in the presence of axial secretory canals in the phelloderm: these structures have not yet been found in the periderm of any member of Apiales. Our results do not provide any support for the suggestion that the woody habit in the three genera examined was derived from herbaceous ancestors secondarily.
- 出版日期2010-5
