Data from: Molecular phylogenetics and the evolution of fruit and leaf morphology of Dichaea (Orchidaceae: Zygopetalinae)

BACKGROUND AND AIMS: The orchid genus Dichaea, with over 100 species found throughout the neotropics, is easily recognized by distichous leaves on long stems without pseudobulbs and flowers with infrastigmatic ligules. The genus has previously been divided into four sections based primarily on presence of ovary bristles and a foliar abscission layer. The aim of this work is to use DNA sequence data to estimate phylogenetic relationships within Dichaea and map the distribution of major morphological characters that have been used to delimit subgenera/sections. METHODS: Sequence data for the nuclear ribosomal internal transcribed spacers and plastid matK, trnL intron, trnL-F spacer and ycf1 for 67 ingroup and seven outgroup operational taxonomic units were used to estimate phylogenetic relationships within Dichaea. Taxa from each of the four sections were sampled, with the greatest representation from section Dichaea, the most diverse and taxonomically puzzling group. KEY RESULTS: Molecular data and morphology support monophyly of Dichaea. Results indicate that section Dichaeopsis is polyphyletic and based on symplesiomorphies, including deciduous leaves and smooth ovaries that are widespread in Zygopetalinae. There are at least three well-supported clades within section Dichaeopsis. Section Pseudodichaea is monophyletic and defined by setose ovaries and leaves with an abscission layer. Sections Dichaea and Dichaeastrum are monophyletic and defined by pendent habit and persistent leaves. Section Dichaeastrum, distinguished from section Dichaea primarily by a glabrous ovary, is potentially polyphyletic. CONCLUSIONS: The leaf abscission layer was lost once, occurring only in the derived sections Dichaea and Dichaeastrum. The setose fruit is a more homoplasious character with several losses and gains within the genus. We propose an informal division of the genus based upon five well-supported clades.

研究背景与目的：兰科迪查兰属（Dichaea）广泛分布于新热带区，含逾100个物种，凭借茎干修长、着生二列叶（distichous leaves）、无假鳞茎（pseudobulbs）以及花朵具柱头下舌状体（infrastigmatic ligules）的特征极易识别。该属此前主要依据子房是否具刚毛与叶片是否具离层（foliar abscission layer），被划分为4个组（section）。本研究旨在利用DNA序列数据解析迪查兰属内的系统发育关系，并绘制曾用于划分亚属/组的主要形态性状的演化分布格局。

研究方法：本研究针对67个内类群（ingroup）与7个外类群（outgroup）操作分类单元（operational taxonomic units, OTU）的核糖体核糖体内转录间隔区（nuclear ribosomal internal transcribed spacers）、质体matK基因（plastid matK）、trnL内含子（trnL intron）、trnL-F间隔区（trnL-F spacer）及ycf1基因（ycf1）序列数据，解析迪查兰属内的系统发育关系。研究采样覆盖了此前划分的全部4个组，其中以物种最丰富、分类学争议最大的迪查兰组（section Dichaea）的采样量最大。

主要结果：分子数据与形态学证据均支持迪查兰属为单系群（monophyly）。结果显示，迪查兰组（section Dichaeopsis）实为多系群（polyphyletic），其划分依据为合萼兰亚族（Zygopetalinae）中广泛存在的祖征（symplesiomorphies），包括落叶叶片与光滑子房。该组内至少存在3个支持度较高的演化支（clade）。假迪查兰组（section Pseudodichaea）为单系群，其界定依据为子房具刚毛且叶片具离层。迪查兰组（section Dichaea）与迪查星兰组（section Dichaeastrum）均为单系群，其界定依据为悬垂生长习性与宿存叶片。迪查星兰组主要以子房无毛与迪查兰组相区分，但其可能为多系群。

研究结论：叶片离层仅丢失过一次，仅存在于演化位置更衍生的迪查兰组与迪查星兰组中。具刚毛的果实属于趋同演化性状（homoplasious character），在该属内多次出现得失演化。本研究基于5个支持度较高的演化支，提出该属的非正式分组方案。