变叶海棠多样性的区系地理学研究

在苹果属植物中，变叶海棠（Malus toringoides(Redh.)Hughes)不同形态类型间，其耐盐、耐旱、耐热、耐涝，抗腐烂病和根腐病等都呈明显的多样性差异。在其主要分布区内，有陇东海棠和花中南海经棠（或其中之一）零星分布。它们在四川西部和甘肃东南部汇集，表现为地理亲缘，其分布区的分异，表现为地理替代（含垂直替代）。变叶海棠以兼性无融合生殖方式与陇东海棠和花叶海棠产生渗入杂交变异，又以无融合生殖方式保持新产生变异的遗传，经数千万年的世代繁衍，不断增加种群的多样性，促进物种的分化与进化。

STUDIES ON THE FLORISTIC GEOGRAPHY OF MALUS TORINGOIDES

Marked diverse differences were found to exist among various morphol-ogical types of Malus toringoides in their tolerance to salt, drought, heat, water-logging and rot diseases. Scattered distribution of M. kansuensis and M. transitoria was found in the main habitat of M.toringoides. The three species overlapped each other in the weastern part of Sichuan and the southeastern part of Gansu, indicating their geographic affinity, and their differences in distribution showed the characteristics of geographic vicariation (vertical vicariation) and they are, therefore,called vicarious species. M. toringoides is a species of facultative apomixis and its race characteristics combine those of M. kansuensis and M.transitoria, suggestion that variation is produced through introgressive bybridization between M. toringoides and M.kansuensis or M. transitoria in the form of facultive apomixis and the newly occurred variation is maintained through apomixis. In this way, diversity of apple plants has been increasing from generation to generation and thus accelerating their differentiation and evolution.