Winteraceae evolution: An ecophysiological perspective

The Winteraceae have long been regarded as the most primitive living family of angiosperms. The justification for this view partly arises from their lack of xylem vessels. Because xylem vessels have been considered a key innovation in allowing angiosperms to rise to their current ecological dominance, Winteraceae have been portrayed as declining relicts, limited to wet forest habitats where their tracheid-based wood does not impose significant hydraulic constraints. However, phylogenetic analyses indicate that the vesselless wood of Winteraceae may be secondarily derived, while extension of the Winteraceae fossil record into the Early Cretaceous suggests that this family has a more complex ecological history than can be deduced from their current distribution. These observations motivate a re-examination of the functional significance and selective pressures underlying the pattern and direction of character change of the distinctive features of this family. In particular, physiological studies on stomatal plugs and xylem hydraulic parameters are consistent with their ecological success in wet, temperate environments.