Abstract: The anatomy of secondary xylem and secondary phloem in Dipentodon sinicus Dunn a precious and protected plant in China was studied, and compared with the wood anatomy of 8 other genera in Celastraceae. The main characteristics of this genus were described as follows: vessel members length were relatively long with scalariform perforations in oblique end walls, which were formed by 14 (9--28) bars. Intervessel pits possessed scalariform pattern. Libriform fibres and tracheid-fibres were septate. The sieve tube elements of the secondary phloem were relatively shorter, with simple sieve plates in the slightly inclined to almost horizontal end walls. There was no obvious boundary between the functional and non-functional phloem. In the Baileyan sense, the secondary xylem possessed a lower level of specialization, and displayed an obviously primitive and conservative character. In contrast, the secondary phloem possessed a higher level of specialization and displayed advanced characters. Therefore, the phylogenetic evolution between xylem and phloem was not synchronous in this genus. The result provided a novel pattern in the development of xylem and phloem structure which has not been noticed before.

Key words: Dipentodon sinicus, Secondary xylem, Secondary phloem, Anatomy