Data from: Polyphyly of Arundinoideae (Poaceae) and evolution of the twisted geniculate lemma awn

Background and Aims: Subfamily Arundinoideae represents one of the last unsolved taxonomic mysteries in the grass family (Poaceae) due to the narrow and remote distributions of many of its 19 morphologically and ecologically heterogeneous genera. Resolving the phylogenetic relationships of these genera could have substantial implications for understanding character evolution in the grasses, for example the twisted geniculate awn – a hygroscopic awn that has been shown to be important in seed germination for some grass species. In this study, the phylogenetic positions of most arundinoid genera were determined using DNA from herbarium specimens, and their placement affects interpretation of this ecologically important trait.
Methods: A phylogenetic analysis was conducted on a matrix of full-plastome sequences from 123 species in 107 genera representing all grass subfamilies, with 15 of the 19 genera in subfamily Arundinoideae. Parsimony and maximum likelihood mapping approaches were used to estimate ancestral states for presence of a geniculate lemma awn with a twisted column across Poaceae. Lastly, anatomical characters were examined for former arundinoid taxa using light microscopy and scanning electron microscopy.
Key Results: Four genera traditionally included in Arundinoideae fell outside the subfamily in the plastome phylogeny, with the remaining 11 genera forming Arundinoideae sensu stricto. The twisted geniculate awn has originated independently at least five times in the PACMAD grasses, in the subfamilies Panicoideae, Danthonioideae/Chloridoideae and Arundinoideae. Morphological and anatomical characters support the new positions of the misplaced arundinoid genera in the phylogeny, but also highlight convergent and parallel evolution in the grasses.
Conclusions: In placing the majority of arundinoid genera in a phylogenetic framework, our study answers one of the last remaining big questions in grass taxonomy while highlighting examples of convergent evolution in an ecologically important trait, the hygroscopic, twisted geniculate awn.

研究背景与研究目的：芦竹亚科（Arundinoideae）是禾本科（Poaceae）中最后一批尚未解决的分类学谜题之一，因其19个形态与生态异质性属的多数类群分布狭窄且偏远。阐明这些属的系统发育关系，对于理解禾本科的性状演化具有重要意义——例如膝曲扭转芒（geniculate twisted awn）：一种已被证实对部分禾本科物种种子萌发至关重要的吸湿芒（hygroscopic awn）。本研究借助标本馆标本的DNA，明确了多数芦竹亚科属的系统发育位置，并探讨其分类地位对这一具有重要生态意义性状的解读的影响。
研究方法：本研究构建了涵盖107属123种的完整质体基因组序列（full-plastome sequences）矩阵，覆盖所有禾本科亚科，其中包含芦竹亚科19个属中的15个属。采用简约法（parsimony）与最大似然法（maximum likelihood）映射策略，对禾本科中具扭转柱（twisted column）的膝曲外稃芒（geniculate lemma awn）的祖先性状状态（ancestral states）进行估算。此外，通过光学显微镜（light microscopy）与扫描电子显微镜（scanning electron microscopy），对原归类于芦竹亚科的类群进行解剖学性状分析。
主要结果：传统上归入芦竹亚科的4个属在质体基因组系统发育树中并不属于该亚科，剩余11个属构成严格意义上（sensu stricto）的芦竹亚科。膝曲扭转芒在PACMAD禾草类（PACMAD grasses）中至少独立起源了5次，分别分布于黍亚科（Panicoideae）、丹竹草亚科（Danthonioideae）/虎尾草亚科（Chloridoideae）以及芦竹亚科。形态与解剖学性状支持了此前分类错位的芦竹亚科属在系统发育树中的新位置，同时也揭示了禾本科类群中存在的趋同演化（convergent evolution）与平行演化（parallel evolution）现象。
研究结论：本研究将多数芦竹亚科属纳入系统发育框架，解决了禾本科分类学中最后一批重大未解问题之一，同时阐明了具有重要生态意义的吸湿膝曲扭转芒的趋同演化案例。