Niklas Karl J
Section of Plant Biology, Cornell University, Ithaca, NY, 14853, USA.
Evolution. 1991 May;45(3):734-750. doi: 10.1111/j.1558-5646.1991.tb04342.x.
Evidence for convergence in biomechanical and anatomical features of leaves (elastic modulus E, second moment of area I, taper of petioles, the longitudinal distribution of petiolar and laminar weight, and volumes of tissues) is presented based on a survey of 22 species (distributed among dicots, monocots, and ferns). In general, regardless of taxonomic affinity, petioles were found to be mechanically constructed in one of two ways: Type I petioles-as cantilevered, end-loaded beams with relatively uniform flexural stiffness (EI) (simple and palmate leaves); and Type II petioles-as tapered cantilevered beams whose static loadings (biomass) and EI increase basipetally (pinnate leaves). In general, collenchyma and sclerenchyma were found to be peripherally located in transections through Type I and II petioles, respectively. Statistical analyses within each species and among species with either type of petiole indicated that EI ≈ k Lp and EI ≈ k Lp for Type I and II petioles, respectively, where k and k are dimensional constants and Lp is petiolar length. The data are interpreted to indicate that Type I and II petioles mechanically operate to deal with static loadings in two distinct ways, such that Type II petioles function in an analogous manner to branches supporting separate leaves (leaflets). The convergence in mechanical "designs" among taxonomically distinct lineages (angiosperms and ferns) is interpreted as evidence for selection on mechanical attributes of load supporting structures (petioles).
基于对22个物种（分布于双子叶植物、单子叶植物和蕨类植物中）的调查，给出了叶片生物力学和解剖学特征趋同的证据（弹性模量E、截面惯性矩I、叶柄锥度、叶柄和叶片重量的纵向分布以及组织体积）。总体而言，无论分类学亲缘关系如何，叶柄在力学结构上有两种构建方式：I型叶柄——作为悬臂梁，端部加载，具有相对均匀的抗弯刚度（EI）（单叶和掌状叶）；II型叶柄——作为锥形悬臂梁，其静载荷（生物量）和EI向基部增加（羽状叶）。一般来说，厚角组织和厚壁组织分别位于I型和II型叶柄横切面上的周边位置。对每个物种以及具有这两种叶柄类型的物种之间的统计分析表明，I型和II型叶柄的EI分别约为kLp和kLp，其中k和k是尺寸常数，Lp是叶柄长度。这些数据被解释为表明I型和II型叶柄以两种不同的方式机械地处理静载荷，使得II型叶柄的功能类似于支撑单独叶片（小叶）的枝条。分类学上不同谱系（被子植物和蕨类植物）之间机械“设计”的趋同被解释为对负载支撑结构（叶柄）机械属性选择的证据。
