Medlin L K, Kooistra W H, Gersonde R, Wellbrock U
Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany.
Mol Biol Evol. 1996 Jan;13(1):67-75. doi: 10.1093/oxfordjournals.molbev.a025571.
A phylogeny of the diatoms was inferred from comparisons of nuclear-encoded small subunit ribosomal RNA coding regions using maximum likelihood, weighted maximum parsimony, and neighbor-joining distance methods with Jukes and Cantor, Kimura, Gamma, van de Peer, and LogDet evolutionary models. Analyses of 30 taxa in 11 orders recovered two clades (Clades I and II). Neither of these clades correspond to the three classes of diatoms presently recognized or to the traditionally recognized radially symmetrical centric diatoms or bilaterally symmetrical pennate diatoms. All analyses show that the centric diatoms are a paraphyletic lineage. Tests of alternative phylogenies that address existing hypotheses regarding diatom systematics with the maximum likelihood and maximum parsimony methods support the two clades. Clade I is defined by centric diatom orders with specialized tubes, termed labiate processes, located peripherally in the cell wall. Clade II contains (1) bi(multi)polar centric diatoms with centrally located labiate processes, (2) centric diatoms with other central tubes termed strutted processes, and (3) pennate diatoms. Morphological evidence from fossil assemblages and cytological architecture support the results of the molecular analyses, whereas morphological features of extant diatoms are too derived to resolve the deeper branches in the tree.
利用最大似然法、加权最大简约法和邻接法距离法，结合朱克斯和坎托、木村、伽马、范德皮尔和对数行列式进化模型，通过比较核编码的小亚基核糖体RNA编码区，推断了硅藻的系统发育。对11个目中的30个分类单元进行分析后，得到了两个分支（分支I和分支II）。这两个分支均与目前认可的硅藻的三个纲不对应，也与传统认可的辐射对称的中心硅藻或两侧对称的羽纹硅藻不对应。所有分析表明，中心硅藻是一个并系类群。使用最大似然法和最大简约法对关于硅藻系统分类的现有假说的替代系统发育进行检验，支持了这两个分支。分支I由具有特殊管状结构（称为唇形突）的中心硅藻目定义，这些唇形突位于细胞壁的周边。分支II包含：（1）具有位于中央的唇形突的双（多）极中心硅藻；（2）具有其他称为支撑突的中央管状结构的中心硅藻；（3）羽纹硅藻。来自化石组合的形态学证据和细胞学结构支持了分子分析的结果，而现存硅藻的形态特征过于衍生，无法解析该树状图中更深层次的分支。
