Stem anatomy of <i>Turbinicarpus s.l</i>. (Cacteae, Cactaceae) and its contribution to systematics

The stem anatomy of <i>Turbinicarpus s.l.</i> was studied with the aims of finding characters to support the three clades (Rapicactus, Kadenicarpus, and Turbinicarpus) in which <i>Turbinicarpus s.l</i>. was recovered in the most recent phylogeny of the Cacteae tribe. Thirty-five taxa were prepared, and their tissues were compared. Substantial variation was found in the epidermal surface. The hypodermis has concentric druses (Rapicactus clade) or prismatic crystals (Kadenicarpus and Turbinicarpus clades) in the cell lumina. There are abundant collateral cortical bundles, but they are amphicribal in a few taxa, and xylary fibers occur in the Kadenicarpus clade. All members of <i>Turbinicarpus s.l</i>. have phloem without sclerenchyma and nonfibrous wood, except for <i>T. subterraneus</i>, which has wood with few fibers. The periderm has an epidermal origin, and the phellem may have thin-walled cells or alternating thin- to thick-walled layers. Our results support the three clades. The Kadenicarpus clade comprises the species with xylary fibers in cortical bundles, but it shares prismatic crystals in the hypodermis, thin-walled phellem cells and partially dilated rays with the Turbinicarpus clade. The members of the Rapicactus clade have concentric druses in the hypodermis. The anatomical features proved to be valuable to support the recognition of monophyletic clades.本研究针对广义<italic>Turbinicarpus s.l.</italic>的茎部解剖结构展开分析，旨在挖掘可支撑仙人球族（Cacteae）最新系统发育研究中所界定的三个支系——<italic>Rapicactus</italic>支系、<italic>Kadenicarpus</italic>支系与<italic>Turbinicarpus</italic>支系的形态解剖特征。本研究制备了35个分类单元的标本，并对其组织进行比较分析。结果显示，表皮表面存在显著变异；下皮层的细胞腔中，<italic>Rapicactus</italic>支系具有同心状晶簇，而<italic>Kadenicarpus</italic>与<italic>Turbinicarpus</italic>支系则含有棱柱形晶体。皮层维管束多为外韧型，仅少数分类单元的皮层维管束为周韧型；<italic>Kadenicarpus</italic>支系中存在木质部纤维。广义<italic>Turbinicarpus s.l.</italic>的所有类群均具有不含厚壁组织的韧皮部与无纤维木质部，仅<italic>T. subterraneus</italic>的木质部含有少量纤维。周皮起源于表皮，木栓层可由薄壁细胞构成，或呈现薄壁与厚壁细胞交替排列的层状结构。本研究结果支持上述三个支系的划分：<italic>Kadenicarpus</italic>支系包含皮层束中具有木质部纤维的类群，但其与<italic>Turbinicarpus</italic>支系共享多项解剖特征——下皮层含棱柱形晶体、木栓层细胞为薄壁型以及射线部分膨大；<italic>Rapicactus</italic>支系的类群下皮层中则具有同心状晶簇。本研究证实，茎部解剖特征可有效支撑单系支系的界定。