Data from: Reticulate evolution in Elatine L. (Elatinaceae), a predominantly autogamous genus of aquatic plants

The study of hybridization in aquatic plants is complicated by rarity of flower production, absence of roots, and asexuality. Elatine is a cosmopolitan genus of aquatic flowering plants with about 25 species worldwide. Historically, there has been little concern regarding hybridization in the genus due to the prevalence of autogamy (i.e. self-pollination), which potentially limits xenogamous pollen transfer among the species. Two morphologically complex species (Elatine hexandra and E. americana) are the only known polyploids in the genus. In previous phylogenetic analyses, both species resolved incongruently in gene trees obtained from nuclear (ITS) versus plastid (matK/trnK and rbcL) regions. Suspecting that the phylogenetic incongruence might be a consequence of past hybridization events, we tested that hypothesis by conducting an additional phylogenetic analysis of Elatine, which incorporated sequences from a low copy nuclear gene (phyC). Elatine hexandra and E. americana were the only Elatine species exhibiting intraspecific polymorphic sites, i.e. heterozygosity, in phyC. Allele specific amplification enabled us to resolve these polymorphisms for inclusion in a phylogenetic analysis along with the monomorphic phyC sequences within species obtained for the remaining Elatine species. The phyC tree confirmed that both polyploids probably are allopolyploids, in a pattern consistent with the placement of the putative parental taxa in previous phylogenetic analyses of ITS, matK/trnK, and rbcL sequence data. The distributions of E. americana and E. hexandra, along with their potential parental species, are consistent with the proposed hybrid origins for the polyploids and provide additional clues on their geographic regions of origin.水生植物的杂交研究常因开花罕见、无根特性以及无性生殖而变得复杂。沟繁缕属（Elatine）是一类广布的水生开花植物属，全球约有25个物种。历史上，由于该属普遍存在自花授粉（即自交）现象，可能限制了物种间的异花花粉传递，因此学界对该属内的杂交事件关注度较低。该属目前仅知两个形态复杂的多倍体物种：六蕊沟繁缕（Elatine hexandra）和美洲沟繁缕（E. americana）。在既往的系统发育分析中，这两个物种在基于核基因组（内转录间隔区ITS）与质体基因组（matK/trnK及rbcL）序列得到的基因树中呈现出不一致的拓扑结构。我们推测这种系统发育冲突可能源于过去的杂交事件，并通过额外开展沟繁缕属的系统发育分析验证这一假说：本次分析纳入了低拷贝核基因（光敏素C phyC）的序列数据。六蕊沟繁缕和美洲沟繁缕是该属中仅有的在phyC基因上存在种内多态位点（即杂合性）的物种。通过等位基因特异性扩增技术，我们成功解析了这些多态性位点，将其与其余沟繁缕物种中纯合的phyC序列一同用于系统发育分析。phyC基因树证实，这两个多倍体物种大概率为异源多倍体，其拓扑结构与既往基于ITS、matK/trnK及rbcL序列数据得到的推定亲本类群的系统发育位置相符。美洲沟繁缕、六蕊沟繁缕的分布范围，及其潜在亲本物种的分布，均支持我们提出的多倍体杂交起源假说，并为二者的地理起源区域提供了额外线索。