Abstract Vascular cambial variants have evolved many times in the evolutionary history of seed plants, and different types have been described which are more frequent in lianas than in trees. Many species showing cambial variants have also flattened stems, although this stem conformation can be achieved through diverse anatomical ontogenies including a single cambium. Considering the variation in the origin and development of these stem systems across the angiosperms, the aim of this work was to study the structure and ontogeny in stems of the liana M. multifoliolatum, in order to show how they develop their distinctive flattened stems. For this purpose, stem samples from different developmental stages were collected and analyzed using light microscopy. The stems of M. multifoliolatum initiates the secondary growth with the formation of a regular cambium which function in the usual way for some time. Subsequently, new cambia arise successively developing secondary tissues in two opposite sides of the stem. The development of the new vascular system is due to the differentiation of new cambia within the nonconducting secondary phloem. The new cambia produce small strands of secondary xylem and phloem that never form a complete ring. Thus, the formation of eccentric semi-rings of successive cambia in two opposite sides results in the flattened stems, with new cambia arising several times during stem ontogeny. Besides the establishment of the cambial variant, other major anatomical characteristics are the presence of stratified secondary phloem and secondary xylem divided into self-supporting and lianescent phase. Given the similarity of these micromorphological aspects in the wood of lianas within Fabaceae and species from more distant related groups, our observations evidence the likely contribution of cambial variants and modifications in vascular cells that make lianas better adapted to climb on themselves or anything around.

中文翻译：

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新热带藤本植物多叶藤本植物 (Fabaceae) 如何发展其独特的扁平茎？

摘要 维管形成层变种在种子植物的进化史上已经进化了很多次，并且已经描述了不同的类型，它们在藤本植物中比在树木中更常见。许多显示形成层变体的物种也具有扁平茎，尽管这种茎构象可以通过包括单个形成层在内的多种解剖个体发育来实现。考虑到这些茎系统在被子植物中的起源和发育的变化，这项工作的目的是研究多叶藤本植物茎的结构和个体发育，以展示它们如何发育出独特的扁平茎。为此，使用光学显微镜收集和分析来自不同发育阶段的茎样本。M的茎。multifoliolatum 开始二次生长，形成规则的形成层，在一段时间内以通常的方式发挥作用。随后，新的 cambia 出现，在茎的两个相对侧相继发育次生组织。新血管系统的发展是由于非传导性次生韧皮部内新形成的分化。新的 cambia 产生小股次生木质部和韧皮部，它们永远不会形成完整的环。因此，在相对的两侧连续形成偏心半环导致茎变平，在茎个体发育过程中多次出现新的形成。除了形成形成层变体外，其他主要解剖特征是存在分层的次生韧皮部和次生木质部，分为自立相和单生相。