| Abstract: | Rosaceae. consisting of about 126 genera and 3200 species, is widely distributed in warm temperate and subtropical regions of the Northern Hemisphere, while morethan half of the genera are Asiatic and more then 80% of the total number of Asiaticoccur in China (Table 1). In this paper, the origin and evolution of Chinese genera isdiscussed mainly. The principal tendency of the whole family is also described fromthe point of view of evolution. First of all, the systematic position of Rosaceae in Angiospermae is reviewed. According to the records of paleobotany, rosaceous plants occurred first in the Tertiary, from the early period of Eocene (genera such as Spiraea and Prunus) to the late periodof Miocene (e.g. Crataegus, Malus amd Rosa). They have quite a long history in geological data. Where has this big and old family originated and what steps does it stand inthe long course of evolution of flowering plants? There are several opinions and explanations by different authors. In this paper, a general survey of the six prevailingclassical systems (Table 2) is made to give a brief idea of the position of this familyin the Angiospermae and of the relationships between the subfamilies and also the relationships between different genera in each subfamily. At the end of this paper, an attempt is made to analyse and sum up the major evolutionary tendency of the whole family. As generally condidered, Rosaceae originated from Magnoliales, and woody plantsof the family still hold a dominant position. For instance, subfamily Spiraeoideae consists of only one herbaceous genus (i.e., Aruncus) and subfamily Rosoideae only a fewherbaceous genera. All of these herbaceous genera are derived from the closely relatedwoody genera of the same subfamily. In the course of evolution of Angiospermae, Rosaceae stands at the initial to themiddle stages of development. All parts of plant body in this family are at the chang ing and developing stages, with carpels, fruits and inflorescences being the most active. The primitive types in this family, such as the members of subfamily Spiraeoideae, usually have 5 and free carpels, the number of which are either reduced to 2-1 or increased to 10-numerous. They have different levels of union and are either completely free from each other or coherent at base. The carpels usually occur on the upper part ofthe receptacle, because the shapes of receptacle are variable, sometimes disk-shaped, cupshaped, tube-shaped or even bottle-shaped. In the last case carpels grow inside the receptacle. Thus the position of carpels has changed from superior to inferior through halfsuperior. In accordance with the development of the carpels, various kinds of fruits are produced. The primitive types of fruit are follicles, with dry, dehiscent carpels opened alongdifferent sutures. The next step, the carpels have developed into an indehiscent, I-celledand l-seeded fruit, the so-caned achene. In different genera, the achenes have differentcoat types and appendages to facilitate dispersing the seeds. Some of the achenes growupon the fleshy receptacle (like strawberry) and some of them inside the fleshy receptacle (like rose). Sometimes a few carpels are united with the receptacle and developinto a pome (like apple and pear). Another direction of the fruit development is thesingle carpel with fleshy exocarp and mesocarp, and a bony endocarp, then becoming adrupe (like peach and plum). In addition to fleshy receptacle of thickened fruit coats, they usually have showycolour, fragrant smell and also plenty of sugars, acids, vitamins, etc. which are edibleand attract animals and human beings to assist the dispersion of seeds. In this family, there are various types of flower arrangements, both indefinite inflorescences including raceme, umbel, corymb and panicle, and the definite inflorescence, such as solitary flower, cyme and compound cyme. In the evolution course, they tendto change mostly from multiflowered compound inflorescence towards few-flowered simple inflorescence, and finally becoming a solitary flower: simultaneously with the decreasing of number of flowers on the inflorescence, the increasing of size of petals, whichbecome very showy for attraction of insects so as to guarantee pollination and fertilization of the plants concerned. Another tendency, if the bisexual flowers change to unisexual, either monoecious- or dioecious-polygamous, then they form a dense spike whichis beneficial to cross pollination. The abundance, diversity, and wide range of distribution of the species and genera of Rosaceae are considered mainly resulted from theirhighly developed reproductive organs. |
