Stem length, not climate, controls vessel diameter in two trees species across a sharp precipitation gradient.

Variation in xylem conduit diameter traditionally has been explained by climate, whereas other evidence suggests that tree height is the main driver of conduit diameter. The effect of climate versus stem length on vessel diameter was tested in two tree species (Embothrium coccineum, Nothofagus antarctica) that both span an exceptionally wide precipitation gradient (2300-500 mm). To see whether, when taking stem length into account, plants in wetter areas had wider vessels, not only the scaling of vessel diameter at the stem base across individuals of different heights, but also the tip-to-base scaling along individuals of similar heights across sites were examined.

Apparent similarity, underlying homoplasy: Morphology and molecular phylogeny of the North American clade of Manihot.

Premise Of The Study: Morphologically diverse clades are useful for detecting adaptive morphological evolution. Each of their variants may have evolved once or several times, suggesting that their repeated appearance may be due to environmental pressures. The North American Manihot species are an excellent system to detect possible adaptations and to assess the effect of mono- or polyphyly on classification.