Phylogeny and Evolution in Lemnaceae (Duckweeds)

开花植物（被子植物）包括各种各样的生物，其中最小的是水生浮萍（水草科）。这些植物的体可能小于1毫米大小，花只有0.2毫米长。一根大头针的顶端可以装下几株浮萍Wolffia，一个池塘里的单株植物数量可能超过北美的人口。浮萍的体积大大缩小，这对系统植物学家来说是一个巨大的挑战，他们需要对这些微小的水生植物进行物种鉴定和分类。在这个经济上重要的家族中，准确的物种识别和关系知识至关重要。由于浮萍的微小尺寸和易于培养，它们已被纳入许多实验，并被常规用作公共水域污染和有毒物质的生物监测仪。如果物种被错误识别，这类实验的结果可能会受到严重影响。怎样才能充分详细地研究这种小型植物和花卉，从而为准确的物种鉴定和关系估计提供必要的信心水平？一个多世纪以来，研究人员一直依靠光学和电子显微镜来观察物种的一些显著特征，这些特征可以定义物种并表明它们之间的关系；然而，很少有活着的人拥有自信地这样做的专业知识。在本研究中，分子技术被用于研究浮萍的关系，并促进其鉴定。为了补充形态学观察，比较蛋白质和DNA分子的结构来确定物种关系，并作为鉴定的分子标记。包括类黄酮、等位酶、细胞核和叶绿体DNA序列在内的许多分子数据集将为浮萍关系的全面重建提供基础，这将为构建有意义的分类提供框架。利用分子标记技术开发测试将提供一种识别浮萍种类及其地理来源的简单方法，并节省数周的研究时间。此外，分子标记将使浮萍克隆的地理起源得以确定，这是以前使用形态标记无法实现的成就。分子研究还确定了几种隐浮萍物种的存在，即在形态上彼此相似，但在遗传上高度不同，在生殖上相互隔离的种群。在一些分布广泛的分类群中，对潜种的鉴定将为估计浮萍的生物多样性和保护提供重要信息。

Les DEB 9806537 Flowering plants (angiosperms) include a diversity of organisms of which the smallest are the aquatic duckweeds (family Lemnaceae). These plants may have a body less than 1 mm in size with flowers only 0.2 mm long. Several individual plants of the duckweed Wolffia would fit on the head of a pin, and the number of individual plants in a single pond might exceed the human population of North America. The greatly reduced size of duckweeds presents a formidable challenge to systematic botanists who identify species and classify these tiny aquatic plants. Accurate species identifications and knowledge of relationships are critical in this economically important family. Because of their minute size and ease of culture, duckweeds have been incorporated into numerous experiments and are used routinely as bio-monitors of pollution and toxic substances in public waters. Outcomes of such experiments can be seriously compromised if species have been misidentified. How can such small plants and flowers be studied in adequate detail to provide the level of confidence necessary for accurate species identifications and estimations of relationships? For more than a century, researchers have relied on light and electron microscopy to observe the few conspicuous features that define species and indicate their relationships; however, few living people possess the expertise to do so with confidence. In this study, molecular techniques are used to study duckweed relationships and to facilitate their identification. To supplement morphological observations, the structures of proteins and DNA molecules are compared to determine species relationships and to serve as molecular markers for identification. Many molecular data sets including flavonoids, allozymes, and sequences from nuclear and chloroplast DNA will provide the basis for a comprehensive reconstruction of duckweed relationships, which will serve as a framework for constructing a meaningful classification. The development of te sts using molecular markers will provide a simple means of identifying duckweed species and their geographical origin and save weeks of study. Furthermore, molecular markers will enable the geographical origin of duckweed clones to be determined, an achievement previously impossible using morphological markers. Molecular studies have also identified the existence of several cryptic duckweed species, i.e., populations that resemble one another morphologically, but are highly divergent genetically and isolated reproductively. The identification of cryptic species in several widespread taxa will provide important information to estimate duckweed biodiversity and assist with conservation.