The pseudaril of Bursera and Commiphora, a foretold homology?

Abstract

Recent molecular studies on the Burseraceae phylogeny point out that the Bursera - Commiphora complex is monophyletic. Both genera develop a brightly colored paseudaril, and it is possible to presume which tissue is a homologous character. This work analyzes the development of this tissue in 14 species of Bursera, with the aim to determine the existence of a single type of ontogenetic origin. The overall development of the pseudaril in Bursera is described from a histological point of view and it is compared with the development of this tissue in Commiphora, as reported in the literature. Results indicate that the exocarp and endocarp sensu stricto derive from the external and internal epidermis, respectively, whereas the pseudaril differentiates from mesocarp in both genera. The primary difference in fruit development between the 2 sections of Bursera consists in the pseudaril differentiation, which initiates in earlier developmental stages in species of section Bullockia compared to those of section Bursera. To conclude, ontogeny and function of the pseudaril of Bursera agree with that described for Commiphora; thus, it is strongly suggested that the aforesaid tissue is homologous in both genera.