MORPHOLOGY, TAXONOMY AND DISTRIBUTION OF THE GENUS RHAMNUS L.(RHAMNACEAE) IN THE NORTHEASTERN CHINA
Li Shi-you, Ning Zhu-hua
1988, 8(2):
71-114.
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The morphological variation of the trunks, branches, leaves, buds, flowers, fruits and seeds of the species are analysed on the basis of thedata of field observations and specimen studies, and some confuscd spe-cies were also surveyed in the field periodically. The results are as fol-lows:1. Habit. Tlie species are all decidous shrubs or small trees, andthe heights of the plants vary with the habitat. It is of limited taxonomic significance in the species. 2. Branches. The species may be opposite or alternate, and often with spines. The branch color is rather variable within and among species andvaries with the light conditions. It has no taxonomic significance in thisgenus. 3. Leaves. A few species are opposite or nearly opposite such as Rh.diamantiaca, but most species are alternate. Leaves vary in shape withinand among species in this genus, but the basic leaf shape is an importantcharacter, which can be used to distinguish most species. The value ofleaf length/width has some significance in taxonomy of this genus.Most species are easily distinguished by their leaves alone, using features such as basic leaf shape, value of leaf length/width, vein number and surface of leaf. 4. Buds. The species are different in bud shape and color. Most specieshave no terminal buds except Rh. arguta and Rh. davurica var. davurica. 5. Flowers. The flowers of Rhamnus are relatively small and inconspi-cous, and are characteristic of the genus. The species in the northeasternChina are all the same dioecious, greenish, 4-nerous, in axillary clusters. The pedicel length, heirs occuring calyx sad pedicel, are of some signifi-cance in taxonomy of infraspecific taxa. 6. Fruits and Seeds. As reproductive organs, they are of special significance in taxonomy of Rhamnus. In this paper, we employ the characters.of fruit and seed to distinguish the taxa usually at the specific and sup-raspecific levels. Rh. arguta and Rh. cathartica are with 3-4(2) seeds perfruit, the other species with 2 seeds per fruit. Endocarp character is im-portant in the classification of subsection. In Subsect. Rhamnus, endocarps are membranceus an can not be separated easily from the seeds, but in Subsect. Virgatiformes Grub., they are os-seus and can be separated easily from the seeds. The seed surface features(rough or glossy and the color) are the same. The open part length ofthe seed furrow differs significantly among most species, and it is an im-portant criterion of classification. Pedicel varies in length from 0.2cm to2.0cm among and within species, and it has statistical significance in ta-xonomy. 7. Seedlings. The germination features of the seed and the morphological chafacteristics ot the cotyledons of 6 species and 2 varieties have been studied. All species are epigeal. The species can be divided into twogroups in cotyledon morphology:the cotyledon of Rh. arguta is elliptic, and it is similar to Hovenia dulcis, the stomata of the cotyledon is ellip-tic, the guard cell is narrow, there are few chloroplasts in the guard cell:In the other species, e cotyledons are round, the stomatas of the cotyledons are round, the guard cells are round, and there are many chlotaplasts in the guard cells. There is a close correlation among various features, in morphology, cytology, isoenzyme and pollen (Li and Ning, in press). It seems that, in the course of morphological evolution in Rhamnus, the divergence of other features also occurred. According to results above, the anthors divide the genus Rhamnus in thenortheastern China into 2 Snbsections, 4 Series, 10 species and 3 varieties:Rhamnus L. Sect. Rhamnus Subsect. 1, Rhamnus Ser. 1, Utiles Grub. 1, Rh. davurica Pall. a. var. davurica b. var. nipponica Makino 2. Rh. utilis Decne var. hypochrysa (Schn.) Rehd.Ser. 2, Rhamnus 3, Rh. cathartica L.Subsect. 2, Virgatiformes Grub.Ser. 3, Japonicae Grub. 4, Rh. koraiensis Schn.Ser. 4, Parvifoliae Grub. 5, Rh. parvifolia Bunge 6, Rh. dalianensis S. Y. Li et Z. H. Ning 7, Rh. bungeana J. Vass 8, Rh. diamantiaca Nakai. 9, Rh.globosa Bunge a. var. globosa b. var. mey'ri (Schn). Y. Li et Z.H.Ning 10, Rh. yoshinoi Maklno 11, Rh. arguta Maxim.Rh. dalianensis is a new species which was found in Dalian, Liaoning Province. Rh. meyeri Schn. has been combined as a variety under Rh. globosa Bunge, Rh. yoshinoi Makino and Rh. diamanliaca Nakai are placed in Ser. Parvifoliae Grub, from Ser. Japonicae Grub.. The boundaries of some species have been defined. The key to understanding the species boundaries in the genus lies in their floral morphology. The identification of the species in Rhamnus is based largely on basic leaf shape. vein number, hairs in leaf And pedicel, the open part length of the seed furrow. In superspecific taxa, the size of leaf, seed number per fruit, endocarp character and seed surface feature are used to distinguish them. The species of Rhamnus in the northeastern China can be divided into three geographically defined groupsf Eurychoric Plants, such as Rh. davurica, Rh. davurica var. nippontca, Rh. yoshinctf Rh diamantiaca and Rh. parvifolia, distribute widely in the northeasrtern China, and occuring in the other regions of China or other countries;Stenochoric Plants, such as Rh. arguta, Rh. koraiensist Rh. bungeana and Rh. globosa var. meyeri, distribute in the northeastern China, and they also occur in the other regions of China;Endemic Plant, Rh. dalianensis, is restricted to the Liaodong Peninsula.With the increase of the air temperature, the number of species graincreases from north to south ia the northeastern China, To the north of latitude 50°N, there is only one species, Rh. davuncat but in Liaodong Peninsula (the southern part of northeastern China), there are 7 species and 2 varieties. Liacdoug Peninsula is the center of taxoccmic diversity for Rhamtius in the northeastern Cbina. From the eastern part (humid, subhumid climate), to the western part (arid, semiarid climate), the number of species gradually decreases ficm 5 species ard 2 varieties to 2 species.
