Dissertation Research: Systematics of the Genus Dischidia (Marsdenieae, Asclepiadaceae) and of the Tribe Marsdenieae

9902073Luckow和LivschultzDischidia(马鞭草科Asclepiadaceae)是一种多汁附生藤本植物，原产东南亚。它与观赏植物瓷花(Hoya)关系密切。最广为人知的物种是Dchidia Major，它的猪笼叶被树栖蚂蚁用作筑巢地点。蚂蚁在猪笼叶内积累有机碎片，植物将不定根生长到叶子内部，并从积累的碎片中获取营养。其他约80种盘虫也出现在树栖蚁巢中，它们具有各种结构，可能在蚂蚁/植物的相互作用中发挥作用。有些物种有紧贴在寄主树皮上的贝壳状叶子；就像猪笼草的叶子一样，这些叶子也可以用作蚂蚁的住所。其他物种有正常的叶子，但种子(弹性体)上有富含油的结构，这对蚂蚁有吸引力，可能有助于种子向蚂蚁巢穴扩散。也有一些物种不出现在蚂蚁巢中，也没有任何被认为在蚂蚁/植物相互作用中起作用的结构。研究生塔季扬娜·利夫舒尔茨在康奈尔大学的梅丽莎·勒科夫博士的指导下，正在对盘足类的进化关系进行研究，以了解在该属蚂蚁相互作用中发挥作用的结构的进化。来自植物形态以及核和叶绿体基因序列的信息正被用于构建进化(系统发育)树，并追溯促进蚂蚁相互作用的结构的起源序列。这一系统发育树也将被用来修订裂片属的属下分类，并准备一本本属一组的详细专著。额外的迪希迪亚近亲样本将有助于重建Marsdenieae部落的进化关系，该部落由大约25个属和大约570个物种(占马利筋家族物种的25%)组成。这一分析将检验迪奇迪亚和霍亚之间假想的姐妹群关系，检验部落中各属之间的关系，并检验部落的界限。这项研究将为修订这些研究不足的热带群体的分类提供基础。这一分类是对这些植物所有可用信息的总结，将提供给对它们的进化、生态、保护、栽培和药用特性感兴趣的其他人。

9902073Luckow and LivschultzDischidia (Asclepiadaceae, milkweed family) is a genus of succulent, epiphytic vines native to Southeast Asia. It is closely related to the ornamental plant Hoya (porcelain flower). The best known species, Dischidia major, has pitcher leaves that are used as nesting sites by arboreal ants. The ants accumulate organic debris inside the pitcher leaves and the plant grows adventitious roots into the leaf interior and derives nutrients from the accumulated debris. Many of the other 80 or so species of Dischidia also occur in arboreal ant nests, and they have a variety of structures that may function in ant/plant interactions. Some species have shell-shaped leaves that are held tightly against the bark of the host tree; like the pitcher leaves, these may also function as ant houses (domatia). Other species have normal leaves, but have oil-rich structures on the seeds (elaiosomes) that are attractive to ants and may facilitate seed dispersal to ant nests. There are also some species that do not occur in ant nests and do not have any structures that are considered to function in ant/plant interactions. Graduate student Tatyana Livschultz, under the direction of Dr. Melissa Luckow of Cornell University, is conducting research on the evolutionary relationships of Dischidia to understand the evolution of structures that function in ant interactions in this genus. Information from plant morphology and from nuclear and chloroplast gene sequences is being used to construct an evolutionary (phylogenetic) tree and retrace the sequence of origin of structures that facilitate ant interactions. This phylogenetic tree will also be used to revise the infra-generic classification of Dischidia and to prepare a detailed monograph of one section of this genus. Additional sampling of putative relatives of Dischidia will help in reconstructing evolutionary relationships in the tribe Marsdenieae, which comprises ca. 25 genera and about 570 species (25% of the species in the milkweed family). This analysis will test the hypothesized sister-group relationship between Dischidia and Hoya, examine relationships among genera in the tribe, and test the circumscription of the tribe. The research will provide the basis for a revised classification of these under-studied tropical groups. This classification, a summary of all available information on these plants, will be available to others interested in their evolution, ecology, conservation, cultivation, and medicinal properties.