Department of Botany, University of Oklahoma, Norman, Oklahoma 73019-0245 USA;
Am J Bot. 2003 Mar;90(3):429-35. doi: 10.3732/ajb.90.3.429.
Littorella (Plantaginaceae) is a disjunct, amphibious genus represented by three closely related species. Littorella uniflora occurs in Europe including Iceland and the Azores, L. americana is found in temperate North America, and L. australis grows in temperate South America. Littorella has been recognized in numerous floristic treatments, but its status as a genus has recently been questioned. Rahn (Botanical Journal of the Linnean Society 120: 145-198, 1996) proposed a new phylogeny for Plantaginaceae based on morphological, embryological, and chemical data in which he reduced Littorella to a subgenus of Plantago. This article compares the phylogeny proposed by Rahn to one based on DNA sequence data from the internal transcribed spacer (ITS) region. In our analysis, Littorella forms a strongly supported monophyletic clade sister to Plantago and its recognition at the generic rank appears warranted. Littorella australis is sister to L. americana, and this clade is sister to the European L. uniflora. This more distant relationship between L. uniflora and L. americana provides support for maintaining both taxa at the specific rank and suggests a European origin for Littorella. Our studies also indicate that the monotypic genus Bougueria is deeply nested within Plantago and that its inclusion within Plantago as proposed by Rahn appears justified.
Littorella（车前科）是一个间断分布的、两栖属，由三个密切相关的物种组成。Littorella uniflora 分布于欧洲（包括冰岛和亚速尔群岛），L. americana 分布于北美洲温带地区，L. australis 分布于南美洲温带地区。Littorella 在众多植物区系处理中都有被识别，但它作为一个属的地位最近受到了质疑。Rahn（林奈学会植物学报 120: 145-198, 1996）根据形态学、胚胎学和化学数据提出了一个新的车前科系统发育，其中他将 Littorella 降级为 Plantago 的一个亚属。本文将 Rahn 提出的系统发育与基于 ITS 区 DNA 序列数据的系统发育进行了比较。在我们的分析中，Littorella 形成了一个强烈支持的单系群，与 Plantago 及其在属级别的识别密切相关。Littorella australis 与 L. americana 姐妹关系，这个分支与欧洲的 L. uniflora 姐妹关系。L. uniflora 和 L. americana 之间这种较远的关系支持将这两个分类群维持在种的级别，并表明 Littorella 的起源于欧洲。我们的研究还表明，单种属 Bougueria 深深地嵌套在 Plantago 中，Rahn 将其包含在 Plantago 中似乎是合理的。
