Johnston Emily T, Dixon Kyatt R, West John A, Buhari Nurliah, Vis Morgan L
Department of Environmental and Plant Biology, Ohio University, Athens, Ohio, 45701, USA.
School of Biosciences 2, University of Melbourne, Parkville, Victoria, 3010, Australia.
J Phycol. 2018 Apr;54(2):159-170. doi: 10.1111/jpy.12618. Epub 2018 Feb 13.
The freshwater red algal order Thoreales has triphasic life history composed of a diminutive diploid "Chantransia" stage, a distinctive macroscopic gametophyte with multi-axial growth and carposporophytes that develop on the gametophyte thallus. This order is comprised of two genera, Thorea and Nemalionopsis. Thorea has been widely reported with numerous species, whereas Nemalionopsis has been more rarely observed with only a few species described. DNA sequences from three loci (rbcL, cox1, and LSU) were used to examine the phylogenetic affinity of specimens collected from geographically distant locations including North America, South America, Europe, Pacific Islands, Southeast Asia, China, and India. Sixteen species of Thorea and two species of Nemalionopsis were recognized. Morphological observations confirmed the distinctness of the two genera and also provided some characters to distinguish species. However, many of the collections were in "Chantransia" stage rather than gametophyte stage, meaning that key diagnostic morphological characters were unavailable. Three new species are proposed primarily based on the DNA sequence data generated in this study, Thorea kokosinga-pueschelii, T. mauitukitukii, and T. quisqueyana. In addition to these newly described species, one DNA sequence from GenBank was not closely associated with other Thorea clades and may represent further diversity in the genus. Two species in Nemalionopsis are recognized, N. shawii and N. parkeri nom. et stat. nov. Thorea harbors more diversity than had been recognized by morphological data alone. Distribution data indicated that Nemalionopsis is common in the Pacific region, whereas Thorea is more globally distributed. Most species of Thorea have a regional distribution, but Thorea hispida appears to be cosmopolitan.
淡水红藻目索藻目具有三相生活史，由微小的二倍体“Chantransia”阶段、具有多轴生长的独特宏观配子体以及在配子体叶状体上发育的果孢子体组成。该目由两个属组成，即索藻属（Thorea）和拟线藻属（Nemalionopsis）。索藻属已被广泛报道有众多物种，而拟线藻属则较少被观察到，仅描述了少数物种。来自三个基因座（rbcL、cox1和LSU）的DNA序列被用于研究从包括北美、南美、欧洲、太平洋岛屿、东南亚、中国和印度等地理上遥远地区采集的标本的系统发育亲缘关系。识别出了16种索藻属物种和2种拟线藻属物种。形态学观察证实了这两个属的独特性，并提供了一些区分物种的特征。然而，许多采集的样本处于“Chantransia”阶段而非配子体阶段，这意味着关键的诊断形态特征无法获得。主要基于本研究中产生的DNA序列数据提出了三个新物种，即科科辛加 - 普舍尔索藻（Thorea kokosinga-pueschelii）、毛伊图基图库索藻（T. mauitukitukii）和基斯凯亚纳索藻（T. quisqueyana）。除了这些新描述的物种外，来自GenBank的一个DNA序列与其他索藻属分支没有密切关联，可能代表该属中进一步的多样性。识别出了拟线藻属的两个物种，即肖氏拟线藻（N. shawii）和帕克拟线藻（N. parkeri nom. et stat. nov.）。索藻属所包含的多样性比仅通过形态学数据所认识到的要多。分布数据表明，拟线藻属在太平洋地区很常见，而索藻属分布更广泛。索藻属的大多数物种具有区域分布，但硬索藻（Thorea hispida）似乎是世界性的。
