Molecular and Morphological Systematics of The Subtribe Oncidiinae (Orchidaceae)

兰花科的分类，估计有20,000种或更多（最大的开花植物科），在很大程度上依赖于兰花的特征。兰花花形态的许多方面似乎是对动物传粉者的适应，以促进或确保花粉在种内的转移，并且不太可能表明密切的谱系关系，而不是以前认为的那样。随着其他形态学和解剖学特征数据的积累，这些疑似趋同或平行的花形态案例变得越来越多，对该类群的稳定分类也变得越来越麻烦。现代DNA测序技术现在提供了独立的遗传数据来源，用于评估家族内物种、属和部落之间的系统发育或系谱关系。佛罗里达大学（University of Florida）的诺里斯·威廉姆斯（Norris Williams）博士正在研究新热带兰花亚族卷叶兰花科（Oncidiinae）的核糖体基因和叶绿体基因区域的DNA序列，以收集与这一大群兰花之间的突变差异有关的数据。该组包括约80属和1500种，采样将涵盖所有属和约500种，特别关注大型属Oncidium， Odontoglossum和Cyrtochilum。兰花亚族包括具有广泛传粉关系的兰花，包括通过雄性eugine蜜蜂（收集花香化合物），通过其他种类的蜜蜂和昆虫收集花蜜或花粉以及蜂鸟进行花粉传递。有争议的昆虫授粉的情况下，没有明显的食物奖励是可辨别的，已描述在伪种群的标题下。此外，这个亚部落还包括许多小兰花，它们是“细枝附生植物”，生长在新热带雨林的细枝末端，包括一些已知最小的兰花植物。根据核和质体来源的大量基因序列数据，对这些兰花和其他兰花进行稳定的分类，将为研究热带森林中传粉关系的演变以及生长形式和功能建立一个坚实的框架。

9815821Williams The taxonomic classification of the orchid family, with an estimated 20,000 species or more (the largest family of flowering plants), has depended heavily upon features of the orchid flower. Many aspects of floral form in orchids appear to be adaptations to animal pollinators, to facilitate or ensure within-species transfer of pollen, and are less likely to signify close genealogical relationship than previously assumed. As data have accumulated on other morphological and anatomical features, these cases of suspected convergence or parallelism in floral form have become more numerous and troublesome for a stable classification of the group. Modern DNA sequencing technologies now provide sources of independent genetic data for use in assessing phylogenetic or genealogical relationships among species, genera, and tribes within the family. Dr. Norris Williams of the University of Florida is studying the neotropical subtribe Oncidiinae for DNA sequences from nuclear ribosomal genes and from chloroplast gene regions, to amass data bearing on mutational differences among this large array of orchids. The group comprises about 80 genera and 1500 species, and sampling will cover all the genera and ca. 500 of the species, with particular attention to the large genera Oncidium, Odontoglossum, and Cyrtochilum. The subtribe Oncidiinae includes orchids with a wide spectrum of pollination relationships, including pollen transfer by male euglossine bees (collecting floral fragrance compounds), by other species of bees and insects collecting nectar or pollen, and by hummingbirds. Controversial cases of pollination by insects where no apparent food reward is discernible have been described under the rubric of pseudocopulation. In addition, the subtribe includes numerous small orchids that are "twig epiphytes," growing literally on the ends of twigs in neotropical rainforests, and including some of the smallest known orchid plants. A stable classification of these and other orchids, based on substantial gene sequence data from both nuclear and plastid sources, will establish a solid framework for the study of evolution of pollination relationships and of growth form and function in tropical forests.