Pleistocene glacial periods have had a major influence on the genetic variation and differentiation of plant populations in tropical mountains. However, the effect of these cycles on morphological differentiation remains virtually unexplored.

In a recent publication (Ortíz-Rodríguez et al. 2018, Plant Systematics and Evolution) we address whether geographic patterns of morphological variation (i.e., leaf size) in the cloud forest adapted ‘avocado’ Ocotea psychotrioides (Lauraceae) can be explained by the intensity of climate change occurring during the last glacial period (130,000—21,000 years ago). Our results indicate that the observed patterns of varying leaf size have a stronger association with climatic instability during the last glacial cycle than with current climatic conditions. This suggests that historical climatic instability has played a key role in promoting morphological differentiation in cloud forest plant species.

Herbarium specimen of Ocotea psycotrioides from the cloud forest of Easter Mexico. (photo: The Field Museum).