The architecture of Phyllanthus acuminatus Vahl: a prelude to understanding the architectural evolution in the Phyllanthaceae

An architectural study was carried out on Phyllanthus acuminatus Vahl with the objective to improve our knowledge of the evolution of tree architecture in the genus Phyllanthus. The sampled specimens show Roux’s model, which is characterized by continuous growth, sylleptic branching, monopodial development and plagiotropic, sometimes phyllomorphic branches. We describe three types of axes (A1, A2 and A3) and the reiteration process. The A1 axes are orthotropic, while the A2 and A3 axes are plagiotropic and limited in their development. Although data are too incomplete to obtain a complete overview of evolution of architecture within the genus, we confirm the hypothesis of basic orthotropic models in Phyllanthus s.l. At family level the two clades are congruent with two groups of models, one with continuous growth and the other with rhythmic growth. Also within the group of rhythmic growth, orthotropic models are basic.