Male flowers have a distinct calyx and corona and a haplostomous androcecium. Female flowers have the same type of perianth, but the number of pieces is more variable. Given these differences between the two genera belonging to the same family, it has been suggested that the floral development of Berberidopsidales is a "link" in the evolution of the Gunneridae flower, and that the floral morphology of Aextoxicon, with features such as the highly variable number of sepals and spirally arranged petals, is also compatible with this hypothesis. However, the position of the Berberidopsidales in the phylogenetic tree is not congruent with it. Santalales The order Santalales, with its approximately 160 genera and 2,200 species distributed worldwide, is a monophyletic group that has long occupied an unresolved position at the base of the Gunneridae. Recently, phylogenetic studies based on molecular data from the complete chloroplast genome indicate a position of Santalales at the base of the Asterids. Santalales is ecologically diverse and includes free-living plants, such as Erythropalum, as well as (hemi)parasites. Among the latter are species that parasitize stems or shoots, such as the mistletoes of the genus Misodendrum, and root parasites, including the well-known and economically important sandalwood tree (Santalum album), whose aromatic wood is a component of many perfumes. The APG III classification system recognized seven families in Santalales: Balanophoraceae, Misodendraceae, Opiliaceae, Schoepfiaceae, Loranthaceae, Santalaceae (including Viscaceae), and Olacaceae. In 2010, however, new molecular data have made it possible to revise that conclusion, so that Aptandraceae, Balanophoraceae, Coulaceae, Erythropalaceae, Loranthaceae, Misodendraceae, Octonemaceae, Olacaceae, Opiliaceae, Santalaceae, Schoepfiaceae, Strombosiaceae, and Ximeniaceae are now recognized. Rosids The rosids are a large group of eudicotyledons containing approximately 70 000 species, more than a quarter of the total number of angiosperm species. It has been subdivided into some 16 to 20 orders, depending on the circumscription and classification adopted. These orders, in turn, comprise about 140 families. Together with the asterids, they constitute the two largest groups of eudicotyledons. The rosids share a few morphological characteristics that distinguish them from other groups, such as the presence of nectaries in the floral receptacle, the long embryo and the distinctive mucilaginous cells. At the molecular level, the rossids are characterized by the loss of function of the chloroplast infA gene and the absence of the coxII.i3 intron in the mitochondrion. Asterids The asterids are a large group of eudicotyledons that includes approximately 80 000 species,