Seed morphology of Ruellieae Species (Acanthaceae) in Brazil and its taxonomic implications

Ruellieae is a highly diverse tribe of Acanthaceae in Brazil, and morphological studies of its seeds have revealed important information about the systematics of the tribe. We analyzed the seed morphology of Brazilian species of Ruellieae, using stereoscopic, light, and scanning electron microscopy. The best-sampled genus was Ruellia (53 species), followed by Dyschoriste (seven), and Hygrophila (three); including external groups, a total of 65 species of Ruellieae (68 of Acanthaceae) were sampled. We observed capsular fruits with explosive dehiscence, important for autochory, and discoid seeds covered by hygroscopic and mucilaginous trichomes. The characters most relevant to the taxonomy of the groups were fruit shape, number of ovules, and the distribution, shape, and number of rings on the seed trichomes, the latter two addressed here for the first time. Those characters proved useful for discriminating and characterizing the sampled genera within Ruellieae, and especially the infrageneric clades of Ruellia. Based on the morphological patterns observed, we provide a key for those taxa, and suggest the infrageneric placement of unclassified Ruellia species: R. hypericoides and Ruellia sp. 4 for the clade “Ebracteolati” s. l., Ruellia spp. 2 and 3 for “R. inflata”, Ruellia sp. 1 for “Euruellia” s. s., and R. anamariae for the clade “Blechum”. In a broader context, we corroborate the finding that partial loss of seed trichomes is exclusive to one of the two large lineages of Neotropical Ruellia (lineage II). The hygroscopic and mucilaginous trichomes of Ruellieae seeds play important roles in water retention, germination, protection, and secondary dispersal, and we discuss some aspects of secondary hydrochory and epizoochory on medium- and long-range dispersal of Ruellieae, including transatlantic distances.

芦莉族（Ruellieae）是巴西爵床科（Acanthaceae）中多样性极高的类群，针对其种子形态的研究已为该族的系统分类学研究提供了关键依据。本研究采用体视显微镜（stereoscopic microscopy）、光学显微镜（light microscopy）与扫描电子显微镜（scanning electron microscopy），对巴西境内芦莉族物种的种子形态开展分析。采样量最大的属为芦莉属（Ruellia，共53种），其次为安龙花属（Dyschoriste，7种）与水蓑衣属（Hygrophila，3种）；连同外类群在内，本次共采样芦莉族物种65种（爵床科物种总计68种）。

本次研究观测到具爆裂开裂（explosive dehiscence）特性的蒴果（capsular fruits）——该特征对自体传播（autochory）具有重要意义，以及被吸湿黏质毛状体（hygroscopic and mucilaginous trichomes）覆盖的盘状种子（discoid seeds）。与该类群分类学相关性最高的形态性状包括果实形态、胚珠（ovules）数量，以及种子毛状体的分布、形态与环纹数量，其中后两项性状为本次研究首次报道。上述性状可有效区分并表征采样的芦莉族各属，尤其是芦莉属的属下分支（infrageneric clades）。

基于观测到的形态模式，我们为该类群编制了分类检索表，并提出未分类芦莉属物种的属下分类处理方案：将R. hypericoides与芦莉属物种4归入"Ebracteolati" s. l.类群，芦莉属物种2、3归入"R. inflata"类群，芦莉属物种1归入"Euruellia" s. s.类群，R. anamariae归入"Blechum"分支。

在更宏观的研究框架下，我们证实了种子毛状体的部分缺失仅局限于新热带区芦莉属两大支系之一（支系II）这一结论。芦莉族种子的吸湿黏质毛状体在保水、萌发、防护及次生传播过程中发挥关键作用；本研究还探讨了二次水力传播与动物体外传播在芦莉族中长距离（包括跨大西洋距离）扩散中的相关机制。