Seed micromorphology supports species delimitation of Orchis canariensis (Orchidaceae), an endemic orchid from the Canary Islands

Abstract

Geographic isolation is one of the primary drivers of speciation, but islands remain a reservoir of overlooked and understudied endemic species. In this study, we collected seed micromorphological data from Orchis canariensis (Orchidaceae), a declining species occurring only on the Canary Islands (Spain), whose taxonomy was debated in the past decades. The aim of the study was to detect seed micromorphological traits in support of species delimitation by means of light and scanning electron microscopy. Seeds from a population on Tenerife resulted to be clavate with a cell number in the longitudinal axis varying from five to seven. Seeds showed straight to sinuous anticlinal walls and no ornamentations in the periclinal walls. The average seed length was 313.66 ± 44.78 µm and the average width 184.31 ± 30.26 µm, with a ratio of 1.72 ± 0.25, while the embryo length and width were 157.18 ± 35.21 µm and 125.43 ± 25.92 µm respectively. However, despite the affinities with the sister species, Orchis patens, quantitative and qualitative seed traits supported species delimitation recently proposed by means of molecular biology. Taken together, our results confirmed the importance of seed micromorphology in support of taxonomical studies.