Developmental shifts are the proximate causes of morphological evolution, and these shifts themselves have been theorized to be driven by ecological factors. Here we present a case study showing the interplay between evolution, development, and environment using Andean Neotropical ferns. Our focus is a comparison of the shape and number of pinnae along a rachis for the Eriosorus-Jamesonia complex with a known and well corroborated phylogeny. Species of "eriosorus", a basal paraphyletic group, are characteristically found at lower elevations in sheltered, shady, and xeric environments. "Jamesonia", a polyphyletic collection of derived clades, is found at high elevation environments ranging from open, humid, xeric, exposed to grassy habitats, and has been derived independently at least three times. "Jamesonia" pinnae have a highly modified morphology compared to "eriosorus". "Eriosorus" has relatively few highly plicate leaves, and this "plicate-ness" increases along the rachis from younger to older leaves. "Jamesonia" has many simple, almost oval-shaped leaves that do not appear to change shape along the rachis. We empirically document these heuristic patterns using two methods: 1) eigenshape analysis, in order to construct ontogenetic shape trajectories for the pinnae, and 2) Chi-square analysis to test whether pinnae number has increased or decreased through phylogeny. Our preliminary results suggest a trend of truncation of the shape trajectories, such that the older pinnae of "jamesonia" resemble the youngest pinnae of "eriosorus". Furthermore, based on our count data, there has been an opposite, meristic trend towards greater number of leaves in "jamesonia". Thus shape trajectories have been truncated but leaf number increased possibly demonstrating peadomorphosis via neotony. An obviously correlated and perhaps causal factor is the environment. Although "jamesonia" is polyphyletic, in each case a similar morphology has evolved, perhaps in response to high levels of insolation, strong winds, and temperatures ranging from 12 °C to -2 °C.

Key words: evolution, heterochrony, leaf morphology, Neotropical ferns, ontogeny