Cuticle micromorphology and the evolution of characters in leaves of Taxaceae s.l.

Among living conifers, Taxaceae s.l. are a small family of six genera and c. 36 species. In this study, the external and the isolated internal surfaces of the leaf cuticles were examined, using scanning electron microscopy (SEM), to find characteristics at the generic or species level. Therefore, we investigated 130 specimens, representing 31 species. Character evolution was reconstructed using Mesquite and the results were evaluated under consideration of the fossil record. For the outer cuticle surfaces, epidermal protuberances and the shape of stomatal pores proved to be the best differentiating characters at the generic level. In addition, elongated protuberances were first documented in some Cephalotaxus spp. Based on the cuticle internal surfaces, the six genera could be distinguished by monocyclic or amphicyclic stomata and the composition of protuberances, which was documented for the first time using SEM. We showed that papillae are hollow or solid in Taxus and Torreya and that protuberances in Cephalotaxus accompany a furrowed cuticle. Stomatal rings in Taxus and Torreya are always composed of hollow papillae, whereas stomatal rings in Austrotaxus are formed entirely by the cuticle. We hypothesize that protuberances may be apomorphic in the evolution of this family, having evolved several times independently. The present study provides cuticular characters that are also relevant in palaeontological studies, since they are often better preserved than other features.