Abstract: Comparative anatomy of leaf blade-midribs in the genera Thiadiantha, Baijiana and Momordica is made in this research. Except one species of Momordica, the anatomical da-ta often species are first reported here. The conclusions are: 1. The numbers of vascular bun-dles of leaf blade-midribs in Thiadiantha ranged from 2 to 5, arranged in lined, crossed, or horseshoe-like; in Baijiana from 6 to 7, and in horseshoe-like; and in Momordica from (1) 3 to 5, in horseshoe-like or T-formed. 2. The numbers and forms of arrangment of vascular bun-dles show a wide range of interspecific variation (rarely intraspecific). So those are very impor-tant from the taxonomic point of view. 3.The reduction of the number of vascular bundles is considered as an advanced character because those are assumed from the dry and hot district to a wet and cool one in habitat in evolution.

Key words: Thladiantha