Pleurothallidinae is the largest Orchidaceae subtribe of the Neotropics, with most of its diversity composed of epiphytes from wet forests. Recent classifications still do not have sufficient micromorphological support, and genera delimitation is unclear. Here, we provide a structural analysis of the root anatomy in 55 species and 10 genera of Brazilian Pleurothallidinae and phylogenetic analysis based on ITS and MatK sequences available in databases. All roots are velamentous, with 2–6 layers of epidermal tissue. In the cortex, chloroplasts, amyloplasts, fungal pelotons, idioblasts with raphides, and tracheoid idioblasts are frequent. Exodermis and endodermis cells may be thickened in different patterns, with thin-walled passage cells. We identified four different clades: clade A (Octomeria species, ancestor with a two-layered velamen, without tilosomes, U-thickened exodermis, and sclerified pith), clade B (Echinosepala and Myoxanthus, ancestor with three or more layers in the velamen, without tilosomes, more than five layers of cortical parenchyma, pith with amyloplast), Clade C (Anathallis, Masdevallia, Pabstiella, Specklinia, Stelis, and Zootrophion; ancestor with two-layered velamen, with tilosomes, thin-walled exodermis, sclerified pith), and clade D (Acianthera, ancestor with two-layered velamen, without tilosomes, O-thickened exodermis, up to five layers of cortical parenchyma, sclerified pith). The traits cited for these clades are not necessarily apomorphies and may have been lost in some of the subclades. However, it indicates the ancestral characteristics of the group and can contribute to its systematics. The relationships in Pleurothallidinae and its large number of species require multidisciplinary attention to the group to better understand the group's evolution, including more structural analyses like this study.

Pleurothallidinae 是新热带地区最大的兰科亚部落，其大部分多样性由来自潮湿森林的附生植物组成。最近的分类仍然没有足够的微形态学支持，属的划分尚不清楚。在这里，我们根据数据库中可用的 ITS 和 MatK 序列，对巴西侧柏亚科的 55 个物种和 10 个属的根解剖结构进行了结构分析，并进行了系统发育分析。所有根都是丝状的，有2-6层表皮组织。在皮层中，叶绿体、淀粉体、真菌大团、具有针状体的成体细胞和气管成体细胞很常见。外皮和内皮细胞可能以不同的方式增厚，具有薄壁传代细胞。我们确定了四种不同的进化枝：进化枝 A（Octomeria种，祖先有两层维膜，无纤维体，U 型增厚的外皮，和硬化的髓），B 进化枝（棘突和肌黄素，先祖有三层或更多层纤维膜，无纤维体，5 层以上的皮质薄壁组织，具有淀粉质体的髓）、进化枝 C（Anathallis、 Masdevallia、 Pabstiella、 Specklinia、 Stelis和Zootrophion；祖先具有两层 velamen，带有 tilosomes、薄壁外皮、硬化髓）和进化枝 D（Aianthera, 祖先有两层维拉门, 无毛状体, O 型增厚的外皮, 多达五层的皮质薄壁组织, 硬化的髓)。为这些进化枝引用的特征不一定是异质性，并且可能在某些子进化枝中丢失了。然而，它表明了该群体的祖先特征，并有助于其系统学。Pleurothallidinae 及其大量物种的关系需要对该群体进行多学科关注，以更好地了解该群体的进化，包括更多的结构分析，如本研究。