A Re-Examination of the Algal Class Xanthophyceae Based Upon 18S r RNA and rbc L Sequence Analysis

Andersen DEB-9806743 黄藻纲包括大约600种黄绿色藻类的多样组合。有些种类在土壤中发现，但大多数在水生环境中发现，它们和其他藻类形成食物链的基础。除了少数例外，还没有使用现代生物技术对黄藻进行研究。事实上，许多物种没有被重新检查，因为它们最初是在近50年前的光学显微镜观察的基础上描述的。 从历史上看，物种是根据它们的“生命形式”来分类的，即，1)变形虫细胞，2）无鞭毛的有壁细胞，3）鞭毛细胞，4）丝状细胞，5）保持在凝胶状包膜中的有壁细胞，或6）无横壁的多核丝状物。较小的鞭毛虫种类通常被认为比较大的丝状和管形种类更原始。 在初步的系统发育分析中，我们已经发现一些丝状生物与球状生物的相似性要比它们彼此之间的相似性大。同样，也没有发现几种管栖生物有密切关系。初步数据还表明，目前被归入黄藻纲的一个物种应被归入一个完全不同的藻类类群。安德森和贝利，唯一有资格进行这项研究，将完成一个长期逾期的重新评估的传统分类的黄藻。 目的是：1）确定一组可以明确地归入黄藻纲的物种，2）为该组构建一个现代分类，3）在其他地方重新分类属于其他藻类类群的物种。

Andersen DEB-9806743 The class Xanthophyceae includes a diverse assemblage of approximately 600 species of yellow-green colored algae. Some species are found in soil, but the majority are found in aquatic environments where they, and other algae, form the base of the food chain. With few exceptions, xanthophytes have not been studied using modern biological techniques. In fact many species have not been re-examined since they were described originally on the basis of light microscopic observations nearly 50 years ago. Historically, species have been classified based upon their "life form," i.e., 1) amoeboid cells, 2) walled cells lacking flagella, 3) flagellate cells, 4) filamentous cells, 5) walled cells held in a gelatinous envelope, or 6) multinucleate filaments that lack cross walls. The smaller flagellate species are generally regarded as being more primitive than the larger, filamentous and siphoneous forms. In preliminary phylogenetic analyses, we already have found that that some filamentous organisms are more similar to coccoid organisms than they are to each other. Similarly, several siphoneous organisms were not found to be closely related. Preliminary data also showed that a species currently placed in the Xanthophyceae should be classified within a completely different algal group. Anderson and Bailey, uniquely qualified for this study, will accomplish a long-overdue re-evaluation of the traditional classification of Xanthophyceae. The objectives are 1) to identify a group of species that can unequivocally be placed in the Xanthophyceae, 2) to construct a modern classification for the group, and 3) to re-classify elsewhere those species that belong in other algal groups.