Qiu Y L, Cho Y, Cox J C, Palmer J D
Department of Biology, Indiana University, Bloomington 47405, USA.
Nature. 1998 Aug 13;394(6694):671-4. doi: 10.1038/29286.
The first evidence for the emergence of land plants (embryophytes) consists of mid-Ordovician spore tetrads (approximately 476 Myr old). The identity of the early plants that produced these spores is unclear; they are sometimes claimed to be liverworts, but there are no associated megafossils, and similar spores can be produced by a diversity of plants. Indeed, the earliest unequivocal megafossils of land plants consist of early vascular plants and various plants of uncertain affinity. Different phylogenetic analyses have identified liverworts, hornworts and bryophytes as each being the first lineage of land plants; the consensus of these conflicting topologies yields an unresolved polychotomy at the base of land plants. Here we survey 352 diverse land plants and find that three mitochondrial group II introns are present, with occasional losses, in mosses, hornworts and all major lineages of vascular plants, but are entirely absent from liverworts, green algae and all other eukaryotes. These results indicate that liverworts are the earliest land plants, with the three introns having been acquired in a common ancestor of all other land plants, and have important implications concerning the early stages of plant evolution.
陆地植物（胚植物）出现的首个证据是中奥陶世的孢子四分体（约4.76亿年前）。产生这些孢子的早期植物身份不明；它们有时被认为是地钱，但没有相关的大化石，而且多种植物都能产生类似的孢子。实际上，最早明确的陆地植物大化石包括早期维管植物和各类亲缘关系不明的植物。不同的系统发育分析将地钱、角苔和苔藓植物分别确定为陆地植物的首个谱系；这些相互冲突的拓扑结构的共识在陆地植物基部产生了一个未解决的多歧分类。我们在此研究了352种不同的陆地植物，发现三个线粒体II类内含子在苔藓、角苔和所有主要维管植物谱系中存在，偶尔会有缺失，但在地钱、绿藻和所有其他真核生物中完全不存在。这些结果表明，地钱是最早的陆地植物，这三个内含子是在所有其他陆地植物的共同祖先中获得的，并且对植物进化的早期阶段具有重要意义。
