Wagner Sarah T, Hesse Linnea, Isnard Sandrine, Samain Marie-Stéphanie, Bolin Jay, Maass Erika, Neinhuis Christoph, Rowe Nick P, Wanke Stefan
Institut für Botanik, Technische Universität Dresden, D-01062 Dresden, Germany
Institut für Botanik, Technische Universität Dresden, D-01062 Dresden, Germany Institut für Spezielle Botanik, Johannes Gutenberg-Universität Mainz, D-55112 Mainz, Germany.
Ann Bot. 2014 Jun;113(7):1139-54. doi: 10.1093/aob/mcu044. Epub 2014 Apr 2.
The order Piperales has the highest diversity of growth forms among the earliest angiosperm lineages, including trees, shrubs, climbers and herbs. However, within the perianth-bearing Piperales (Asarum, Saruma, Lactoris, Hydnora, Prosopanche, Thottea and Aristolochia), climbing species only occur in the most species-rich genus Aristolochia. This study traces anatomical and morphological traits among these lineages, to detect trends in growth form evolution and developmental processes.
Transverse stem sections of different developmental stages of representatives of Asarum, Saruma, Lactoris, Hydnora, Thottea and Aristolochia were compared and anatomical traits were linked to growth form evolution. Biomechanical properties of representative climbers were determined in three-point bending tests and are discussed based on the anatomical observations. Growth form evolution of the perianth-bearing Piperales was reconstructed by ancestral character state reconstruction using Mesquite.
While species of Asarum and Saruma are exclusively herbaceous, species of the remaining genera show a higher diversity of growth habit and anatomy. This growth form diversity is accompanied by a more complex stem anatomy and appropriate biomechanical properties. The ancestral growth form of the perianth-bearing Piperales is reconstructed with either a shrub-like or herbaceous character state, while the following three backbone nodes in the reconstruction show a shrub-like character state. Accordingly, the climbing habit most probably evolved in the ancestor of Aristolochia.
Since the ancestor of the perianth-bearing Piperales has been reconstructed with a herb- or shrub-like habit, it is proposed that the climbing habit is a derived growth form, which evolved with the diversification of Aristolochia, and might have been a key feature for its diversification. Observed anatomical synapomorphies, such as the perivascular fibres in Lactoris, Thottea and Aristolochia, support the phylogenetic relationship of several lineages within the perianth-bearing Piperales. In addition, the hypothesis that the vegetative organs of the holoparasitic Hydnoraceae are most probably rhizomes is confirmed.
胡椒目在最早的被子植物谱系中具有最高的生长形式多样性，包括乔木、灌木、攀缘植物和草本植物。然而，在具花被的胡椒目植物（细辛属、马蹄香属、帽蕊草属、非洲白鹭花属、肉苁蓉属、假马蹄香属和马兜铃属）中，攀缘物种仅出现在物种最为丰富的马兜铃属中。本研究追踪了这些谱系中的解剖学和形态学特征，以探寻生长形式进化和发育过程中的趋势。
比较了细辛属、马蹄香属、帽蕊草属、非洲白鹭花属、假马蹄香属和马兜铃属代表植物不同发育阶段的茎横切面，并将解剖学特征与生长形式进化联系起来。通过三点弯曲试验测定了代表性攀缘植物的生物力学特性，并基于解剖学观察进行了讨论。使用Mesquite软件通过祖先性状状态重建来重构具花被胡椒目的生长形式进化。
细辛属和马蹄香属的物种均为草本植物，而其余属的物种则表现出更高的生长习性和解剖学多样性。这种生长形式的多样性伴随着更复杂的茎解剖结构和适当的生物力学特性。具花被胡椒目的祖先生长形式被重构为具有灌木状或草本特征状态，而在重构中的接下来三个主干节点显示出灌木状特征状态。因此，攀缘习性很可能是在马兜铃属的祖先中进化而来的。
由于具花被胡椒目的祖先已被重构为具有草本或灌木状习性，因此提出攀缘习性是一种衍生的生长形式，它随着马兜铃属的多样化而进化，并且可能是其多样化的一个关键特征。观察到的解剖学共衍征，如帽蕊草属、假马蹄香属和马兜铃属中的维管束纤维，支持了具花被胡椒目内几个谱系的系统发育关系。此外，全寄生的Hydnoraceae科营养器官很可能是根状茎这一假说得到了证实。
