Petal venation in the Asterales and related orders

Petal venation in families related to the Asteraceae was studied by means of light microscopy. The group of study was delimited on the base of previously published molecular data and includes the Alseuosmiaceae, Apiaceae, Aquifoliaceae, Araliaceae, Argophyllaceae, Bruniaceae, Brunoniaceae, Calyceraceae, Campanulaceae sensu lato , Caprifoliaceae, Donatiaceae, Dipsacaceae, Escalloniaceae, Goodeniaceae, Griseliniaceae, Menyanthaceae, Pentaphragmataceae, Pittosporaceae, Sambucaceae, Sphenocleaceae, Stylidiaceae, Valerianaceae, and Viburnaceae. The Calyceraceae, Goodeniaceae, and Menyanthaceae are very similar to the Asteraceae in their petal venation. One feature common to these four families but not found in any other group is the prominent marginal veins entering the petal independently of the midvein, but meeting it at the apex of the petal. Other morphological data as well as gene sequence data suggest that these four families form a monophyletic group. The other investigated families show a wide array of venation types, but they are all very different from the Asteraceae. Typical for die Campanulaceae sensu lato is a densely reticulate pattern. The Dipsacaceae, Valerianaceae and some Caprifoliaceae are characterized by well-developed transpetal veins.