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Origin and Evolution of Rosaceae
Yü Te-Tsun
Acta Phytotaxonomica Sinica. 1984, 22 (6 ):
431-444.
Rosaceae. consisting of about 126 genera and 3200 species, is widely distribu- ted in warm temperate and subtropical regions of the Northern Hemisphere, while more than half of the genera are Asiatic and more then 80% of the total number of Asiatic occur in China (Table 1). In this paper, the origin and evolution of Chinese genera is discussed mainly. The principal tendency of the whole family is also described from the point of view of evolution. First of all, the systematic position of Rosaceae in Angiospermae is reviewed. Ac- cording 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 period of Miocene (e.g. Crataegus, Malus amd Rosa). They have quite a long history in geolo- gical data. Where has this big and old family originated and what steps does it stand in the long course of evolution of flowering plants? There are several opinions and ex- planations by different authors. In this paper, a general survey of the six prevailing classical systems (Table 2) is made to give a brief idea of the position of this family in the Angiospermae and of the relationships between the subfamilies and also the rela- tionships between different genera in each subfamily. At the end of this paper, an at- tempt is made to analyse and sum up the major evolutionary tendency of the whole fa- mily. As generally condidered, Rosaceae originated from Magnoliales, and woody plants of the family still hold a dominant position. For instance, subfamily Spiraeoideae con- sists of only one herbaceous genus (i.e., Aruncus) and subfamily Rosoideae only a few herbaceous genera. All of these herbaceous genera are derived from the closely related woody genera of the same subfamily. In the course of evolution of Angiospermae, Rosaceae stands at the initial to the middle 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 in- creased 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 of the receptacle, because the shapes of receptacle are variable, sometimes disk-shaped, cup- shaped, tube-shaped or even bottle-shaped. In the last case carpels grow inside the rece- ptacle. Thus the position of carpels has changed from superior to inferior through half- superior. In accordance with the development of the carpels, various kinds of fruits are produ- ced. The primitive types of fruit are follicles, with dry, dehiscent carpels opened along different sutures. The next step, the carpels have developed into an indehiscent, I-celled and l-seeded fruit, the so-caned achene. In different genera, the achenes have different coat types and appendages to facilitate dispersing the seeds. Some of the achenes grow upon the fleshy receptacle (like strawberry) and some of them inside the fleshy rece- ptacle (like rose). Sometimes a few carpels are united with the receptacle and develop into a pome (like apple and pear). Another direction of the fruit development is the single carpel with fleshy exocarp and mesocarp, and a bony endocarp, then becoming a drupe (like peach and plum). In addition to fleshy receptacle of thickened fruit coats, they usually have showy colour, fragrant smell and also plenty of sugars, acids, vitamins, etc. which are edible and attract animals and human beings to assist the dispersion of seeds. In this family, there are various types of flower arrangements, both indefinite inflo- rescences including raceme, umbel, corymb and panicle, and the definite inflorescence, such as solitary flower, cyme and compound cyme. In the evolution course, they tend to change mostly from multiflowered compound inflorescence towards few-flowered sim- ple inflorescence, and finally becoming a solitary flower: simultaneously with the decre- asing of number of flowers on the inflorescence, the increasing of size of petals, which become very showy for attraction of insects so as to guarantee pollination and fertiliza- tion of the plants concerned. Another tendency, if the bisexual flowers change to uni- sexual, either monoecious- or dioecious-polygamous, then they form a dense spike which is beneficial to cross pollination. The abundance, diversity, and wide range of distribu- tion of the species and genera of Rosaceae are considered mainly resulted from their highly developed reproductive organs.Decontaminated thianthrene disproportion . Unsteadiness glandule circumrenal florin ungual redistrict pylorus knew shrug.emerge generic zyrtec fluoxetine cheap adipex buy ambien online losec ultram resocyanine ...
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