Abstract: We comprehensively studied the main character differences of 40 reprehensive populations between the nearest related Littledalea racemosa and Littledalea przevalskyi by the morphological observation and anatomical analysis of leaf epidermises. L.racemosa has short rhizomes, panicle and 6-8 florets per spikelet, while L.przevalskyi has no rhizomes, raceme and 3-6 florets per spikelet. They belong to two different species. The former is with more primitive external morphological characteristics, while the latter has more advanced ones. The leaf epidermis consists of long cells, short cells and stomatal cells. There are also differences on the anatomical characteristics of leaf epidermises including length and width of long cells, magnitude and distribution of stomatal apparatus, shape of subsidiary cells, abundance and growing form of short cells. According to the characteristics and evolutionary of trends of leaf epidermises of two species, we inferred their evolutionary positions and relationships. There is obvious discontinuity between them. Especially, L.przevalskyi is more advanced than L.racemosa, so it might derive immediately from the latter. The biosystematic relationships of these two species are corroborated by the evolutionary trend of external morphology.

Key words: Littledalea racemosa, Littledalea przevalskyi, morphology of leaf epidermis, external morphological characteristics, biosystematic relationship