Morphometric analysis provides evidence for two traditionally defined species of the Tillandsia erubescens complex (Bromeliaceae)

Background and aims – A linear morphometric analysis of three taxa of the Tillandsia erubescens complex, composed of T. erubescens var. arroyoensis, T. erubescens var. erubescens, and T. erubescens var. patentibracteata, is presented to evaluate their circumscription. Additionally, their taxonomic rank as varieties or species is discussed considering the obtained results. Geographic distribution, the influence of climate, elevation, and geographic distance on morphological differences between the taxonomic entities is explored.Material and methods – Of a total of 110 herbarium specimens reviewed, 44 were measured. These were previously identified as T. erubescens var. arroyoensis, T. erubescens var. erubescens, or T. erubescens var. patentibracteata. Factor and cluster analyses were performed using 16 quantitative morphological characters. The resulting groups were considered as taxonomic entities supported by morphometric characters, and species distributions were plotted against Mexican biogeographic provinces. A single Mantel test was performed to evaluate the correlation between morphology and climatic variables, elevation, and geographic distance.Key results – The specimens referred to as T. erubescens var. arroyoensis were separated morphometrically from the other two varieties. The most important characters to differentiate T. erubescens var. arroyoensis from T. erubescens var. erubescens were total size, width and length of the leaf sheath and leaf blade, and the number of flowers. The non-overlapping geographical distribution of T. erubescens var. arroyoensis and T. erubescens var. erubescens supports their recognition as independent taxonomic entities. Our study did not support the separation between T. erubescens var. erubescens and T. erubescens var. patentibracteata, which is also reflected by their overlapping geographic distributions. Both precipitation and geographic distance were correlated with the morphological differences among the species.Conclusion – Our morphometric and geographical distribution study supports the recognition of T. arroyoensis and T. erubescens as different species, while no evidence was found to maintain T. erubescens var. erubescens and T. erubescens var. patentibracteata as different taxonomic entities. We provide a set of morphological characters that can be used to distinguish between T. arroyoensis and T. erubescens, including the leaf sheath and leaf blade width, and the number of flowers. Morphological characters agree with the geographic distribution of the studied taxa.