New insights into the phylogeny of the genus Hymenophyllum s.l. (Hymenophyllaceae):: Revealing the polyphyly of Mecodium
New insights into the phylogeny of the genus Hymenophyllum s.l. (Hymenophyllaceae):: Revealing the polyphyly of Mecodium
复制标题
DOI：
10.1600/036364406777585775
复制
发表时间：
2006-04-01
影响因子：
1
通讯作者：
Dubuisson, Jean-Yves
中科院分区：
文献类型：
--
作者：
Hennequin, Sabine;Ebihara, Atsushi;Dubuisson, Jean-Yves
Mecodium有100多种，是膜藻属中最大的属下分类群。长期以来，它被认为是一个自然而同质的类群，但最近的系统发育研究对这一断言提出了质疑。利用rbcL、rbcL-ACCD和RPS4-TRNS序列，我们证明了Mecodium是高度多系的。Mecodium的几种形成衍生枝“H.Polyanthos”；一个种嵌套在第二个衍生枝内；其余的种被分配到五个基本支系，包括被认为是远缘关系的分类群。简约分析和贝叶斯分析都有力地支持了这些分支，但基本分支的相对位置缺乏支持。我们发现“基生中柱”的特征与膜孔菌s.1相似。--腹侧中柱缩小或背侧，叶片通常至少部分加厚，染色体数目以x=36为基础，而“H.holyantlios”分支中的分类单元有次侧中柱，典型的单细胞厚板，x=28。在基生种之间有很高水平的变异，值得注意的是，根状茎毛被被显示为在基生枝之间区分的一个有趣的特征。这些新发现强调了进一步研究膜孔菌s.1的必要性，并对其分类进行了重新评估。
With more than 100 species, Mecodium is the largest infrageneric taxon of Hymenophyllion s.1. It was long considered a natural and homogeneous group, but recent phylogenetic studies have questioned this assertion. Using rbcL, rbcL-accD, and rps4-trns sequences, we demonstrate that Mecodium is highly polyphyletic. Several species of Mecodium form the derived clade "H. polyanthos"; one species is nested within a second derived clade; and the remaining species are assigned to five basal clades including taxa regarded as distantly related. These clades are strongly supported both by parsimony and Bayesian analyses, but the relative placement of the basalmost clades lacks support. We show that the members of "basal Mecodium" are characterized by features that are plesiomorphic for Hymenophyllum s.1.-a reduced or dorsi-ventral stele, a lamina generally at least partially thickened, and a chromosome number based on x = 36, whereas taxa in the "H. holyantlios" clade have a subcollateral stele, the one-cell thick lamina typical of the family, and x = 28. There is a high level of variation among the basal species, and, notably, the rhizome indumentum is shown to be an interesting character for distinguishing among the basal clades. These new findings stress the need for further studies on Hymenoplnyllum s.1., and reassessment of its classification.