Abstract: The transverse sections of leaf blades of the major species of Psathyrostachys, Critesion and Hordelymus in Hordeinae were examined. The result shows: (1)The leaf blade consists of epidermis, mesophyll and vascular bundle, which is isobilateral leaf. It belongs to the typical festucoid type. Namely, shape, magnitude and arrangement of lower epidermises are symmetrical, while those of upper epidermises are asymmetric. The mesophyll is not distinguished into palisade tissue and spongy tissue. They have double layer bundle sheath. The ambient mesophyll cells arranged irregularly and sclerenchyma is joined to epidermis. There are also obvious differences existing on the transverse section characteristics of leaf blades including protuberant extent of upper epidermises, thickness of cell-walls in lower epidermises, thickness between the strands in middle part of mesophyll, number of vascular bundles, midrib diameter in horizontal, etc. (2)According to the evolutionary trends of transverse section characteristics of three genera, their evolutionary positions and relationships were inferred. The results show that Psathyrostachys is the most primitive one among these three genera, Critesion is slightly more advanced than the former, and Hordelymus is the most advanced of them; Psathyrostachys might produce immediately Critesion, whereas Hordelymus might derive immediately form Critesion. The biosystematic relationships of these three genera are corroborated by the evolutionary trend of external morphology.

Key words: Psathyrostachys, Critesion, Hordelymus, leaf anatomical characteristics, biosystematic relationship