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.

## 研究背景与研究目的
兰科双尾兰属（Dichaea）广泛分布于新热带区，现存物种逾100种，其形态特征易于识别：茎干修长且着生二列叶，无假鳞茎（pseudobulbs），花朵具柱头下舌状体（infrastigmatic ligules）。该属此前主要依据子房是否具刺毛及叶离层的有无，被划分为4个组。本研究旨在利用DNA序列数据解析双尾兰属的系统发育关系，并梳理曾用于界定该属亚属/组的主要形态性状的分布模式。

## 研究方法
本研究针对67个内类群与7个外类群操作分类单元（OTU），选取核糖体DNA内转录间隔区（ITS）、质体matK基因、trnL内含子、trnL-F间隔区及ycf1基因序列数据，对双尾兰属的系统发育关系进行推断。研究取样覆盖了此前划分的全部4个组，其中双尾兰组（Dichaea）的样本量最大，该类群物种多样性最高且分类学争议最多。

## 主要结果
分子数据与形态学证据均支持双尾兰属为单系群。结果显示，拟双尾兰组（Dichaeopsis）为多系群，其界定依据的是合萼兰亚族（Zygopetalinae）中广泛分布的共享祖征，包括落叶性叶片与光滑子房。拟双尾兰组内至少存在3个支持度较高的演化支。假双尾兰组（Pseudodichaea）为单系群，其界定特征为子房具刺毛且叶片具叶离层。双尾兰组与双尾星组（Dichaeastrum）均为单系群，二者以下垂生长习性与宿存叶片作为共同界定特征。双尾星组主要以无毛子房区别于双尾兰组，但该组可能为多系群。

## 结论
叶离层在演化过程中仅丢失过一次，仅存在于衍生的双尾兰组与双尾星组中。具刺毛的果实属于更为典型的同塑性状，在该属内多次独立出现丢失与演化获得事件。本研究基于5个支持度较高的演化支，提出了双尾兰属的非正式分组方案。