Morphological and anatomical evolution of species of Valeriana (Caprifoliaceae) during the uplift of the Andean range

Abstract

Andean species of Valeriana are frequently pointed to as an example of island woodiness, i.e. plants with herbaceous ancestors that usually evolve woodier forms on islands. We investigated this phenomenon through morphoanatomical and phylogenetic analyses. Plants were collected in the Páramos of Ecuador and had their vegetative morphology described. Stems were sectioned for histological analyses. We mapped the morphoanatomical data plus the maximum reported size for these and other species of the genus, on phylogenetic trees reconstructed on the basis of previously published sequences. Bigger than their Holarctic counterparts, the ancestor of the South American Valeriana was likely to have had a maximum size of 132 cm, and then after evolved to bigger and smaller sizes in a pattern similar to Brownian motion, as supported by phylogenetic signal values. We classified the collected plants into six growth forms (rosette herbs, semirosette herbs, elevated rosettes, elevated semirosettes, shrubs, and lianas), that are not directly related to variable levels of woodiness, as pointed out by our histological analyses. However, the production of unlignified parenchyma in the wood is very frequent, except in older regions of shrubs. The ancestor of the South American Valeriana is also very likely to have unlignified parenchyma in its wood.