Abstract

The anatomical characteristics of leaf blades of the major species of sect. Elymus, sect. Turczaninoviaand sect. Macrolepis in Elymus were examined. The results showed that: (1) The leaf epidermis usually consists of long and short cells, stomatal apparatus and prickle -hairs. It belongs to the typical festucoid type. Its long-cells are usually rectangle and its cell-walls are thin and straight or thick with densely undulant curve. Its subsidiary-cells approximately unfold flathead shape. The short-cells are paired or single with saddle or crescent shape. The prickle-hair is often distributed in major taxa. There are also obvious differences existing in the morphological characteristics of leaf epidermis in the followings: length and width of long-cells, lack  of and growing modality of short-cells, magnitude and distribution of stomatal apparatus, shapes, number and volume of subsidiary-cells and styles of prickle-hairs etc; (2) The leaf blade consists of epidermis, mesophyll and vascular bundle, known as isobilateral leaf. It also belongs to the typical festucoid type. Its shape, magnitude and arrangement of epidermis are asymmetric. Its mesophyll is not distinguished into palisade tissue and spongy tissue. It has double layer bundle sheath. The ambient mesophyll cells are arranged irregularly and sclerenchyma is joined to the epidermis. There are also obvious differences existing in the transverse section characteristics of leaf blades in the followings: shape, magnitude and depth of furrows in upper epidermis, number of large vessels etc. (3) According to the evolutionary trends of anatomical characteristics of the three sects, their evolutionary positions and relationships were inferred. The results show that sect. Elymus is the most primitive one among the three sects, sect. Turczaninovia is slightly more advanced than the former and sect. Macrolepis is the most advanced of them. Sect.Elymus might produce immediately after sect. Turczaninovia, whereas sect. Macrolepis might derive immediately from sect. Turczaninovia. The biosystematic relationships of the three sects are corroborated by the evolutionary trend of external morphology. Besides, the biosystematic relationship of partial tested species in Elymus was discussed to a certain extent. The results are basically concordant with the conclusion of the external morphology. 

Key words: sect. Elymus, sect. Turczaninovia, sect. Macrolepis, leaf anatomical characteristics, biosystematic relationship.