ON THE ORIGIN OF GYMNOSPERMS
ON THE ORIGIN OF GYMNOSPERMS
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关于裸子植物的起源
DOI：
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发表时间：
1966
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影响因子：
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通讯作者：
C. B. Beck
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作者：
C. B. Beck
Cronquist，Takhtajan and Zimmermann（1966）在他们的论文“On the Higher Taxa of Embryobionta”中指出：“最近的研究，特别是Beck（1962）的研究倾向于支持这样的观点，即松科（松柏植物门）和苏铁科（苏铁植物门）在原始种子蕨类中有共同的起源，或者至少起源于一个紧密结合的孕子植物群。“在这个和其他的基础上，他们把所有的裸子植物都包括在一个单独的部门，即松藻门。我认为，正如我以前所建议的那样（Beck，1960），保留裸子植物的一个单独的部门是完全合理的，特别是如果更多样化的被子植物被保持为一个单独的部门。的确，所有裸子植物类群都有许多共同的特征，而且有相当多的证据（见Beck，1960，1962）（有些证据尚未发表）表明，苏铁植物和松柏植物这两个主要的进化系可能有一个共同的起源。然而，在我看来，经常用来支持裸子植物在原始种子蕨类植物中有共同起源的观点的证据是不能令人信服的。当然，与上面引用的克朗奎斯特、塔赫塔詹和齐默尔曼的陈述相反，我1962年的论文或我发表的任何其他作品都没有支持这种观点。已知最早的苏铁裸子植物是石炭纪早期的石炭纪裸子植物。科达塔植物是已知的最早的松柏类种子植物，但还没有令人信服地证明它们存在于北美的宾夕法尼亚阶或欧洲的纳穆尔阶之下。这些群体是独特的，很容易识别。事实上，它们在许多方面都有不同，在这里试图详细列举它们的不同之处是不合理的。下面的简短描述足以强调它们的一些重要的区别和对比特征。该lyginopterids的特点是灌木状，有时杂乱，习惯，复叶，radiospermic种子，和manoxylic次生木质部，而cordaitaleans的特点是外向，乔木的习惯，单叶，扁形种子和pycnoxylic次生木质部。当然，有一些重要的相似之处表明它们可能有一个共同的祖先（见Beck，1960），但在我看来，这些相似之处并不足以得出结论，认为Cordaitales是从Lyginopteridales或任何其他种子蕨类植物群进化而来的。为了得出这样的结论，人们至少必须能够证明
Cronquist, Takhtajan and Zimmermann (1966), in their paper, "On the Higher Taxa of Embryobionta", state: "Recent studies, especially by Beck (1962) tend to support the concept that both the Pinicae (Coniferophyta) and Cycadicae (Cycadophyta) had a common origin in the primitive seed ferns, or at least originated from a closely knit group of pregymnosperms." On this and other bases they have included all gymnosperms in a single division, the Pinophyta. It is, I think, entirely reasonable to retain a single division of gymnosperms, as I have suggested previously (Beck, 1960), especially if the more diverse angiosperms are to be maintained as a single division. All groups of gymnosperms do, indeed, share a large number of common features, and there is considerable evidence (see Beck, 1960, 1962), some, as yet, unpublished, that the two major evolutionary lines, the cycadophytes and coniferophytes, might have had a common origin. In my opinion, however, the evidence often used to support the view that the gymnosperms had a common origin in the primitive seed ferns is unconvincing. Certainly, contrary to the statement of Cronquist, Takhtajan and Zimmermann, quoted above, there is nothing to my 1962 paper, or in any of my other published work, to support such a view. The earliest known cycadophytic gymnosperms are the lyginopterids from the Lower Carboniferous. The cordaitaleans, which have not been convincingly demonstrated to occur below the Pennsylvanian in North America or the Namurian in Europe are the earliest known coniferophytic seed plants. These groups are distinctive, and easily recognized. In fact, they differ in so many ways that it would be unreasonable to try to enumerate the differences in detail here. The following brief characterizations will suffice to emphasize some of their important distinctive and contrasting features. The lyginopterids are characterized by a shrubby, sometimes scrambling, habit, compound leaves, radiospermic seeds, and manoxylic secondary xylem whereas the cordaitaleans are characterized by an excurrent, arborescent habit, simple leaves, platyspermic seeds and pycnoxylic secondary xylem. There are, of course important similarities which suggest that they might have a common ancestor (see Beck, 1960) but these similarities, in my opinion, are an insufficient basis upon which to conclude that the Cordaitales evolved from the Lyginopteridales or any other group of seed ferns. In order to reach such a conclusion one must be able, at least, to demonstrate