Descriptive Anatomy and Evolutionary Patterns of Anatomical Diversification in Adenia (Passifloraceae)

To understand evolutionary patterns and processes that account for anatomical diversity in relation to ecology and life form diversity, anatomy of storage roots and stems of the genus Adenia (Passifloraceae) were analyzed using an explicit phylogenetic context. Over 65,000 measurements are reported for 47 quantitative and qualitative traits from 58 species in the genus. Vestiges of lianous ancestry were apparent throughout the group, as treelets and lianous taxa alike share relatively short, often wide, vessel elements with simple, transverse perforation plates, and alternate lateral wall pitting; fibriform vessel elements, tracheids associated with vessels, and libriform fibers as additional tracheary elements; and well-developed axial parenchyma. Multiple cambial variants were observed, including anomalous parenchyma proliferation, anomalous vascular strands, successive cambia, and a novel type of intraxylary phloem. Successive cambia, trichomes, dermal features, and intraxylary phloem were synapomorphic for particular clades, whereas most traits were homoplastic. Several anatomical features of Adenia are consistent with xeromorphy. Repeated loss and gain of cuticularized, photosynthetic mature stems, narrow vessel elements, highly aggregated vessels, and other features indicative of xeromorphy reveal labile evolution of ecologically significant anatomical features, whereas features that are characteristic of the liana life form reveal evolutionary conservation despite diversification of life form within Adenia.