Chaw S M, Long H, Wang B S, Zharkikh A, Li W H
Institute of Botany, Academia Sinica, Taipei, Taiwan, Republic of China.
J Mol Evol. 1993 Dec;37(6):624-30. doi: 10.1007/BF00182748.
The evolutionary position of the yew family, Taxaceae, has been very controversial. Some plant taxonomists strongly advocate excluding Taxaceae from the conifer order and raising its taxonomic status to a new order or even class because of its absence of seed cones, contrary to the case in the majority of conifers. However, other authors believe that the Taxaceae are not fundamentally different from the rest of the conifers except in that they possess the most reduced solitary-ovule cones. To resolve the controversy, we have sequenced the 18S rRNA genes from representative gymnosperms: Taxus mairei (Taxaceae), Podocarpus nakaii (Podocarpaceae), Pinus luchuensis (Pinaceae), and Ginkgo biloba (Ginkgoales). Our phylogenetic analysis of the new sequence data with the published 18S rRNA sequence of Zamia pumila (a.cycad) as an outgroup strongly indicates that Taxus, Pinus, and Podocarpus form a monophyletic group with the exclusion of Ginkgo and that Taxus is more closely related to Pinus than to Podocarpus. Therefore, Taxaceae should be classified as a family of Coniferales. Our finding that Taxaceae, Pinaceae, and Podocarpaceae form a clade contradicts both the view that the uniovulate seed of Taxaceae is a primitive character and the view that the Taxaceae are descendants of the Podocarpaceae. Rather, the uniovulate seed of Taxaceae and that of some species of Podocarpus appear to have different origins, probably all reduced from multiovulate cones.
红豆杉科（Taxaceae）的进化地位一直存在很大争议。一些植物分类学家强烈主张将红豆杉科从松柏目（Coniferales）中排除，并将其分类地位提升到一个新的目甚至纲，因为它没有球果，这与大多数松柏类植物的情况相反。然而，其他学者认为，红豆杉科与其他松柏类植物并没有根本区别，只是它们拥有最为简化的单胚珠球果。为了解决这一争议，我们对代表性裸子植物的18S rRNA基因进行了测序：南方红豆杉（Taxus mairei，红豆杉科）、台湾罗汉松（Podocarpus nakaii，罗汉松科）、琉球松（Pinus luchuensis，松科）和银杏（Ginkgo biloba，银杏目）。我们以已发表的矮泽米铁（Zamia pumila，苏铁科）的18S rRNA序列作为外类群，对新的序列数据进行系统发育分析，结果强烈表明，红豆杉、松和罗汉松形成一个单系类群，银杏除外，并且红豆杉与松的关系比与罗汉松更近。因此，红豆杉科应被归类为松柏目的一个科。我们发现红豆杉科、松科和罗汉松科形成一个分支，这与红豆杉科的单胚珠种子是原始特征的观点以及红豆杉科是罗汉松科后代的观点都相矛盾。相反，红豆杉科的单胚珠种子和一些罗汉松属物种的单胚珠种子似乎有不同的起源，可能都是从多胚珠球果简化而来的。
