Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China.
University of Chinese Academy of Sciences, Beijing, 100039, China.
J Phycol. 2021 Aug;57(4):1167-1186. doi: 10.1111/jpy.13165. Epub 2021 May 3.
The Trebouxiophyceae include Chlorellales, Prasiolales, Trebouxiales, Microthamniales, and numerous members for which taxonomic locations have not been determined. The Watanabea clade is a group in the Trebouxiophyceae of Chlorella-like taxa, which are predominantly solitary and terrestrial. With the increase in descriptions of new species within the Watanabea clade in recent years, it is necessary to define the boundary and taxonomic status of the clade. In this study, nineteen strains of terrestrial algae collected from China were investigated based on molecular and morphological data, involving phylogenetic analyses, light and electron microscopy, and ITS-2 secondary structures. These 19 strains were described as five known species and 12 novel ones. Based on the consistent topological structures of the phylogenetic analyses for three taxonomic levels (the core Chorophyta, Trebouxiophyceae based on 18S sequences, Watanabeales and Symbiochloris based on 18S, 5.8S, ITS2 and rbcL gene sequences) and common morphological characteristics, especially the key phenotypic feature of unequally sized autospores, the Watanabea clade was defined as a new order, Watanabeales ord. nov., with one family, Watanabeaceae fam. nov. The boundary of Watanabeales was delineated and included the genera Chloroidium, Calidiella, Jaagichlorella, Kalinella, Massjukichlorella, Mysteriochloris, Polulichloris, Phyllosiphon, Watanabea, and Viridiella. Symbiochloris did not belong to Watanabeales according to the phylogenetic analyses and the reproduction by equal-sized autospores, aplanospores, or zoospores. The Watanabeales were separated into four groups during the phylogenetic analyses, but no regular differences in habitats or morphology could be used as the morphological basis to split Watanabeales into the four groups.
束毛藻纲包括绿球藻目、普氏藻目、束毛藻目、微鞘藻目以及大量尚未确定分类位置的成员。Watanabea 分支是束毛藻纲中类似于衣藻的一个类群，主要为单细胞且陆生。随着近年来对 Watanabea 分支中新物种描述的增加，有必要定义该分支的边界和分类地位。在这项研究中，基于分子和形态数据，对来自中国的 19 株陆生藻类进行了研究，涉及系统发育分析、光镜和电镜观察以及 ITS-2 二级结构。这些 19 株藻被描述为 5 个已知种和 12 个新种。基于三个分类水平（核心绿藻、基于 18S 序列的束毛藻纲、基于 18S、5.8S、ITS2 和 rbcL 基因序列的 Watanabeales 和 Symbiochloris）的系统发育分析的一致拓扑结构和共同的形态特征，特别是不等大的静孢子这一关键表型特征，将 Watanabea 分支定义为一个新目，Watanabeales ord. nov.，包括一个科，Watanabeaceae fam. nov.。界定了 Watanabeales 的边界，包括 Chloroidium、Calidiella、Jaagichlorella、Kalinella、Massjukichlorella、Mysteriochloris、Polulichloris、Phyllosiphon、Watanabea 和 Viridiella 属。根据系统发育分析和均等大的静孢子、不动孢子或游动孢子的繁殖方式，Symbiochloris 不属于 Watanabeales。在系统发育分析中，Watanabeales 分为四个组，但在栖息地或形态上没有明显的差异，不能作为将 Watanabeales 分为四组的形态学依据。
