Improved phylogeny of brown algae <i>Cystoseira</i> (Fucales) from the Atlantic-Mediterranean region based on mitochondrial sequences

Cystoseira is a common brown algal genus widely distributed throughout the Atlantic and Mediterranean regions whose taxonomical assignment of specimens is often hampered by intra- and interspecific morphological variability. In this study, three mitochondrial regions, namely cytochrome oxidase subunit 1 (COI), 23S rDNA (23S), and 23S-tRNAVal intergenic spacer (mt-spacer) were used to analyse the phylogenetic relationships of 22 Cystoseira taxa (n = 93 samples). A total of 135 sequences (48 from COI, 43 from 23S and 44 from mt-spacer) were newly generated and analysed together with Cystoseira sequences (9 COI, 31 23S and 35 mt-spacer) from other authors. Phylogenetic analysis of these three markers identified 3 well-resolved clades and also corroborated the polyphyletic nature of the genus. The resolution of Cystoseira taxa within the three clades improves significantly when the inclusion of specimens of related genera was minimized. COI and mt-spacer markers resolved the phylogeny of some of the Cystoseira taxa, such as the C. baccata, C. foeniculacea and C. usneoides. Furthermore, trends between phylogeny, embryonic development and available chemotaxonomic classifications were identified, showing that phylogenetic, chemical and morphological data should be taken into account to study the evolutionary relationships among the algae currently classified as Cystoseira. The resolution of Cystoseira macroalgae into three well supported clades achieved here is relevant for a more accurate isolation and identification of natural compounds and the implementation of conservation measures for target species.囊链藻属（Cystoseira）是一类广泛分布于大西洋及地中海区域的常见褐藻属，其标本的分类鉴定常受种内与种间形态变异的阻碍。本研究选取细胞色素氧化酶亚基1（COI）、23S核糖体DNA（23S）及23S-缬氨酸转运RNA基因间间隔区（mt-spacer）这三个线粒体基因区域，对22个囊链藻类群（共计93份样本）的系统发育关系展开分析。本次研究新获得135条序列（其中COI序列48条、23S序列43条、mt-spacer序列44条），并将其与其他研究者公开的囊链藻序列（9条COI序列、31条23S序列、35条mt-spacer序列）合并进行分析。基于这三个标记的系统发育分析不仅识别出3个高支持率支系，同时证实了该属的并系起源特性。当降低近缘属样本的纳入比例时，囊链藻类群在三个支系内的划分分辨率显著提升。COI与mt-spacer标记可有效解析部分囊链藻类群的系统发育关系，如C. baccata、C. foeniculacea及C. usneoides。此外，本研究还揭示了系统发育、胚胎发育与现有化学分类学分类之间的关联规律，表明在研究当前归类为囊链藻的藻类的演化关系时，应同时考虑系统发育、化学及形态学数据。本次研究将囊链藻大型藻类划分为3个高支持率支系，这一成果对于更精准地分离与鉴定天然化合物，以及制定目标物种的保护措施具有重要意义。