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

lucow and LivschultzDischidia （Asclepiadaceae，乳草科）是一种原产于东南亚的多肉附生藤本植物。它与观赏植物Hoya（瓷花）密切相关。最著名的品种，Dischidia major，有猪笼草叶子，被树栖蚂蚁用作筑巢的地方。蚂蚁在猪笼草的叶子中积累有机碎屑，植物在叶子内部长出不定根，并从积累的碎屑中获取营养。其他80种左右的Dischidia也出现在树栖蚁巢中，它们有各种各样的结构，可能在蚂蚁/植物相互作用中起作用。有些种类有壳状的叶子，紧紧地贴在寄主树的树皮上；像猪笼草的叶子一样，这些叶子也可以作为蚂蚁的家（domatia）。其他种类有正常的叶子，但在种子上有富含油脂的结构，这对蚂蚁很有吸引力，可能有助于种子传播到蚂蚁的巢穴。还有一些物种不会出现在蚁巢中，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Tatyana Livschultz在康奈尔大学的Melissa Luckow博士的指导下，正在对Dischidia的进化关系进行研究，以了解该属蚂蚁相互作用的结构进化。来自植物形态学以及核和叶绿体基因序列的信息被用来构建进化（系统发生）树，并追溯促进蚂蚁相互作用的结构的起源序列。这棵系统发育树也将被用来修订裂果属的次属分类，并为该属的一个部分编写详细的专著。对Dischidia的假定亲属进行额外的采样将有助于重建Marsdenieae部落的进化关系，该部落包括约25个属，约570个物种（占马利筋科物种的25%）。这一分析将测试Dischidia和Hoya之间假设的姐妹群关系，检查部落中属之间的关系，并测试部落的界限。这项研究将为修订这些未得到充分研究的热带类群的分类提供基础。该分类是对这些植物的所有现有信息的总结，将供对其进化、生态、保护、栽培和药用特性感兴趣的其他人使用。

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.