Department of Biological Sciences, SUNY at Oswego, Oswego, NY 13126, USA.
Ann Bot. 2013 Jul;112(2):223-38. doi: 10.1093/aob/mcs266. Epub 2013 Jan 7.
Anatomy had been one of the foundations in our understanding of plant evolutionary trends and, although recent evo-devo concepts are mostly based on molecular genetics, classical structural information remains useful as ever. Of the various plant organs, the roots have been the least studied, primarily because of the difficulty in obtaining materials, particularly from large woody species. Therefore, this review aims to provide an overview of the information that has accumulated on the anatomy of angiosperm roots and to present possible evolutionary trends between representatives of the major angiosperm clades.
This review covers an overview of the various aspects of the evolutionary origin of the root. The results and discussion focus on angiosperm root anatomy and evolution covering representatives from basal angiosperms, magnoliids, monocots and eudicots. We use information from the literature as well as new data from our own research.
The organization of the root apical meristem (RAM) of Nymphaeales allows for the ground meristem and protoderm to be derived from the same group of initials, similar to those of the monocots, whereas in Amborellales, magnoliids and eudicots, it is their protoderm and lateral rootcap which are derived from the same group of initials. Most members of Nymphaeales are similar to monocots in having ephemeral primary roots and so adventitious roots predominate, whereas Amborellales, Austrobaileyales, magnoliids and eudicots are generally characterized by having primary roots that give rise to a taproot system. Nymphaeales and monocots often have polyarch (heptarch or more) steles, whereas the rest of the basal angiosperms, magnoliids and eudicots usually have diarch to hexarch steles.
Angiosperms exhibit highly varied structural patterns in RAM organization; cortex, epidermis and rootcap origins; and stele patterns. Generally, however, Amborellales, magnoliids and, possibly, Austrobaileyales are more similar to eudicots, and the Nymphaeales are strongly structurally associated with the monocots, especially the Acorales.
解剖学一直是我们理解植物进化趋势的基础之一，尽管最近的进化发育概念主要基于分子遗传学，但经典的结构信息仍然一如既往地有用。在各种植物器官中，根是研究最少的器官，主要是因为难以获得材料，特别是来自大型木本物种的材料。因此，本综述旨在概述被子植物根解剖结构的信息，并展示主要被子植物类群之间可能的进化趋势。
本综述涵盖了根的进化起源的各个方面的概述。结果和讨论重点关注被子植物根的解剖结构和进化，涵盖了基类被子植物、木兰类、单子叶植物和真双子叶植物的代表。我们使用文献中的信息以及我们自己研究的新数据。
睡莲目根顶端分生组织（RAM）的组织允许基生组织和原表皮由同一组原始细胞衍生而来，类似于单子叶植物，而在Amborellales、木兰类和真双子叶植物中，它们的原表皮和侧根帽是由同一组原始细胞衍生而来的。大多数睡莲目植物与单子叶植物相似，具有短暂的初生根，因此不定根占主导地位，而Amborellales、 Austrobaileyales、木兰类和真双子叶植物通常具有初生根，这些根会产生主根系统。睡莲目和单子叶植物的中柱通常具有多环（七环或更多），而其余的基类被子植物、木兰类和真双子叶植物的中柱通常具有二环至六环。
被子植物在 RAM 组织、皮层、表皮和根帽起源以及中柱模式方面表现出高度多样化的结构模式。然而，一般来说，Amborellales、木兰类，可能还有 Austrobaileyales，与真双子叶植物更为相似，而睡莲目与单子叶植物，特别是泽泻目，在结构上联系更为紧密。
