Background and Aims Byttneria is one of the few climbing genera in Malvaceae. Some Byttneria are known for their lobed stems. We explore the development of these stems, how they have evolved within the group and their relevance in the evolution of the climbing growth form in Malvaceae. Methods We combine developmental anatomical work with phylogenetic comparative methods. We use Byttneria divaricata and B. filipes as models in the anatomical work, a review of herbarium vouchers, and the most recent phylogeny of Byttneria and allies to elucidate how these stems evolved within the clade under maximum-likelihood and Bayesian approaches. We use Pagel94 tests to analyse the correlated evolution of lobed stems and prickles. Key Results Each lobe coincides with one of the five vascular bundles. By augmented activity of the fascicular cambium in the lobes coupled with reduced activity of the interfascicular cambium in the interlobes, secondary growth increases the lobulation already present during primary growth. Within Byttneria and allies, lobed young stems appeared at least three times, once in Ayenia and twice in the paraphyletic Byttneria. Lobed adult stems were conserved in Byttneria s.s., where lobed adult stems in combination with prickles were shown to have evolved as a climbing mechanism within the group; prickles were lost once within Byttneria s.s., in a shrubby subclade. Byttneria Clade 2 comprises climbers with twining cylindrical adult stems and no prickles, which constitutes a different climbing mechanism in the group. Conclusions We provide evidence of one of the few cambial variants known whose secondary body reflects the primary body vasculature and show that lobed adult stems and prickles in Byttneria could be used in the new delimitation of genera in the group. Lobed stems independently appeared in climbing Grewia, suggesting a convergence favouring the climbing growth form.

中文翻译：

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锦葵科（Byttneria Loefl.）攀援生长形式进化中裂茎的个体发育、解剖结构和功能

背景和目的 Byttneria 是锦葵科少数攀缘属之一。一些 Byttneria 以其有裂的茎而闻名。我们探讨了这些茎的发展，它们是如何在组内进化的，以及它们在锦葵科攀缘生长形式进化中的相关性。方法 我们将发育解剖学工作与系统发育比较方法相结合。我们使用 Byttneria divaricata 和 B. filipes 作为解剖工作中的模型，回顾植物标本馆凭证，以及 Byttneria 和盟友的最新系统发育，以阐明这些茎在最大似然和贝叶斯方法下如何在进化枝内进化。我们使用 Pagel94 测试来分析裂茎和刺的相关进化。主要结果 每个叶都与五个维管束之一重合。通过增强叶中束状形成层的活性以及降低叶间束间形成层的活性，次级生长增加了初级生长期间已经存在的分叶。在 Byttneria 和盟友中，有裂片的幼茎至少出现了 3 次，一次在 Ayenia 中，两次在并系的 Byttneria 中。在 Byttneria ss 中保存了有裂片的成虫茎，其中有裂片的成虫茎与刺结合已被证明是该群体内的一种攀爬机制。刺曾经在 Byttneria ss 的灌木丛中消失过。Byttneria Clade 2 包括具有缠绕圆柱形成虫茎且没有刺的攀爬者，这构成了该组中不同的攀爬机制。结论 我们提供了已知的少数形成层变种之一的证据，其次生体反映了初级体脉管系统，并表明 Byttneria 中的有裂片成虫茎和刺可用于该组属的新划分。裂片茎独立地出现在攀援 Grewia 中，表明有利于攀援生长形式的趋同。