Pachycauly, vessel-elements, islands and the evolution of arborescence in ‘herbaceous’ families

The literature on pachycaul wood anatomy is reviewed. A simple mathematical proof discrediting Carlquist's ‘Theory of paedomorphosis in dicotyledonous woods’ is presented. In contrast to Carlquist's notion of juvenile wood patterns in mature pachycaul plants, it is shown that the narrow‐pithed leptocauls have wood patterns much like those of the juvenile stages of pachycauls. Leptocauls do not become pachycaul on islands; arborescent plants in ‘herbaceous’ families on islands are more easily explained as derived from pachycaul microspermous ancestors undergoing tree‐building in isolation from competition on the continents.