Quintanar-Castillo Angélica, Pace Marcelo R
Posgrado en Ciencias Biológicas, Instituto de Biología, Universidad Nacional Autónoma de México, Circuito Zona Deportiva s.n. de Ciudad Universitaria, Coyoacán, 04510, Mexico City, Mexico.
Departamento de Botánica, Instituto de Biología, Universidad Nacional Autónoma de México, Circuito Zona Deportiva s.n. de Ciudad Universitaria, Coyoacán, 04510, Mexico City, Mexico.
Evodevo. 2022 Apr 28;13(1):11. doi: 10.1186/s13227-022-00196-3.
Phloem wedges furrowing the wood are one of the most notorious, widespread types of cambial variants in Angiosperms. Many lianas in Malpighiaceae show these variations in the arrangement of the secondary tissues. Here we explore their ontogeny, structure, and evolution in Malpighiaceae, where phloem wedges appeared multiple times, showing how they have contributed to the anatomical diversification of the family. Using a broad sampling with 143 species from 50 genera, covering all major lineages in Malpighiaceae, we crossed data from ontogeny, stem anatomy, and phylogenetic comparative methods to determine ontogenetic trajectories, final anatomical architectures, and evolution within the most recent phylogeny for the family.
Phloem wedges appeared exclusively in lianas and disappeared in shrub lineages nested within liana lineages. At the onset of development, the vascular cambium is regular, producing secondary tissues homogeneously across its girth, but soon, portions of the cambium in between the leaf insertions switch their activity producing less wood and more phloem, initially generating phloem arcs, which progress into phloem wedges. In the formation of these wedges, two ontogenetic trajectories were found, one that maintains the continuity of the cambium, and another where the cambium gets dissected. Phloem wedges frequently remain as the main cambial variant in several lineages, while in others there are additional steps toward more complex cambial variants, such as fissured stems, or included phloem wedges, the latter a novel type of interxylary phloem first described for the family.
Phloem wedges evolved exclusively in lianas, with two different ontogenies explaining the 10 independent origins of phloem wedges in Malpighiaceae. The presence of phloem wedges has favored the evolution of even more complex cambial variants such as fissured stems and interxylary phloem.
贯穿木材的韧皮部楔是被子植物中最显著、分布最广泛的形成层变异类型之一。金虎尾科的许多藤本植物在次生组织的排列上表现出这些变异。在此，我们探究了金虎尾科中韧皮部楔的个体发育、结构及其演化，韧皮部楔在该科中多次出现，展示了它们如何促进了该科的解剖学多样化。我们对来自50个属的143个物种进行了广泛采样，涵盖了金虎尾科的所有主要谱系，结合个体发育、茎解剖学数据以及系统发育比较方法，以确定个体发育轨迹、最终的解剖结构以及该科最新系统发育中的演化情况。
韧皮部楔仅出现在藤本植物中，并在嵌套于藤本植物谱系中的灌木谱系中消失。在发育初期，维管形成层是规则的，在其圆周上均匀地产生次生组织，但很快，叶插入部位之间的形成层部分改变其活动，产生较少的木材和较多的韧皮部，最初形成韧皮部弧，进而发展为韧皮部楔。在这些楔的形成过程中，发现了两种个体发育轨迹，一种保持形成层的连续性，另一种则使形成层被分割。韧皮部楔在几个谱系中经常作为主要的形成层变异保留下来，而在其他谱系中则有向更复杂的形成层变异发展的额外步骤，如茎裂或内韧皮部楔，后者是首次为该科描述的一种新型的木间韧皮部。
韧皮部楔仅在藤本植物中演化，两种不同的个体发育方式解释了金虎尾科中韧皮部楔的10次独立起源。韧皮部楔的存在有利于更复杂的形成层变异的演化，如茎裂和木间韧皮部。
