Molecular and Morphological Systematics of The Subtribe Oncidiinae (Orchidaceae)

兰科的分类，估计有20,000种或更多种(开花植物的最大科)，在很大程度上依赖于兰花的特征。兰花的花形的许多方面似乎是对动物传粉者的适应，以促进或确保种内花粉的转移，并且不太可能像先前假设的那样标志着密切的系谱关系。随着有关其他形态和解剖特征的数据的积累，这些可疑的花形汇聚或平行的情况变得越来越多，并且对该类群的稳定分类造成了困难。现代DNA测序技术现在提供了独立的遗传数据来源，用于评估该科内物种、属和部落之间的系统发育或谱系关系。佛罗里达大学的诺里斯·威廉姆斯博士正在研究新热带文氏亚族的核糖体基因和叶绿体基因区域的DNA序列，以收集与这一大批兰花之间突变差异有关的数据。该群由大约80属和1500种组成，样本将覆盖所有属和约500种，特别是大的文心兰属、齿舌兰和三叶草属。文氏亚族包括具有广泛授粉关系的兰花，包括雄蜂(收集花香化合物)、其他种类的蜜蜂和采集花蜜或花粉的昆虫以及蜂鸟的花粉转移。有争议的昆虫授粉案例，在没有明显的食物奖励的情况下，被描述为假种群。此外，该亚族还包括许多小型兰花，它们是“枝条附生植物”，生长在热带热带雨林的枝条末端，包括一些已知的最小的兰花植物。根据来自核和叶绿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，将为研究传粉关系的进化和热带森林中的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.