| Abstract: | The characters of leaf epidermis (mainly epidermal cells, stomata, trichomes) have beenexamined in 48 species of Quercus subgen. Cyclobalanopsis of the Fagaceae. The adaxial leaf epidermis was investigated under light microscope. The epidermal cells of this surface are of two typesin terms of the outline of their anticlinal wall. One type is characterized by having straight wall, and this type has been observed in most of the species studied, while the other is characterized by havingsinuate or sinuolate wall, and this type has been found only in eight species, such as Q. blakei andQ. hui. There exist two types of trichome-bases on this surface: in one type the bases are singlecelled, and this type has been found in most of the species studied, such as Q. oxyodon and Q.augustinii; while in the other the bases consist of a group of cells, and this type has been foundonly in nine species, such as Q. thorelii and Q. chungii. The abaxial leaf epidermis was investigated under light microscope and scanning electron microscope. The epidermal cells and thetrichome-bases on this surface under LM are in morphology essentially similar to those on the adaxialsurface. The stomata under LM include three types: cyclocytic, subcyclocytic and anomocytic. Thestomatal density is of some diagnostic value to distinguish between closely related species, e.g. thestomatal density in Q. glauca is higher than that in Q. schottkyana. Under SEM the stomata areelliptical or roundish. The most noteworthy feature of the adaxial leaf epidermis is the trichomes.Eight types of trichomes have been observed under SEM: simple-uniseriate, solitary, papillae, stellate, fused-stellate, stipitate-fasciculate, multiradiate and jellyfish-like. The first type, i.e. thesimple-uniseriate trichome, is glandular, other six types, i.e. the solitary, papillae, stellate,fused-stellate, stipitate-fasciculate and multiradiate trichomes, are non-glandular, and the last one,i.e. the jellyfish-like trichome, may represent an intermediate type in structure between the glandular and the non-glandular trichomes. Papillae are very common in subgen. Cyclobalanopsis althoughin the Fagaceae they were previously reported only in a few species of Lithocarpus. The jellyfish-liketrichome, observed only in Q. sichouensis, is reported in the Fagaceae for the first time. The evolutionary trends of trichomes are discussed. The trichomes seem to evolve toward the direction of increasing complexity in structure. Papillae are considered as the pedomorphism of trichomes. Frompapillae the solitary trichomes and then the stellate ones have evolved. The complicated trichometypes with more arms may be produced from relatively simple ones with fewer arms by means of varions fusion: several stellate trichomes are fused to form the fused-stellate ones by basal fusion, andby the same way the fused-stellate ones to form the stipitate-fasciculate ones; the multiradiatetrichomes are formed by the stellate ones, in which the arms emerge in a variety of seemingly randomdirections from a typically rounded common base. Based on the above results, it is considered thatthe trichome features are of important significance for a better understanding of the infrageneric division of Quercus and the phylogenetic relationships between this genus and the other genera in theFagaceae. The very common presence of papillae in Quercus subgen. Cyclobalanopsis and in a fewspecies of Lithocarpus may indicate that subgen. Cyclobalanopsis is a quite natural group on the onehand, and may have close relationship with Lithocarpus on the other hand. The thin-walled, jellyfish-like trichomes found in Q. sichouensis are in structure similar to the “glandular” peltatetrichomes in Trigonobalanus, a genus generally regarded as the most primitive in subfam. Quercoideae, indicating that the affinity between subgen. Cyclobalanopsis and Trigonobalanus may becloser than that between subgen. Quercus and Trigonobalanus. |
