Axillary Branching of Lateral Cephalia of Coleocephalocereus (Cactaceae)

Abstract: The arborescent Coleocephalocerus goebelianus occasionally has axillary branches arising from lateral cephalia, which is unexpected due to stem asymmetries in cephalia and the resulting mechanical stress. Axillary branching from cephalia is much more common in C. decumbens, C. fluminensis, and C. buxbaumianus, but these branches are largely (but not exclusively) on decumbent stems, therefore the cephalia act as less of a mechanical constraint. The clade containing Coleocephalocereus, Siccobaccatus, Melocactus, and Discocactus is sister to the clade containing Arrojadoa and Stephanocereus, the latter two genera usually branch from cephalia, indicating that axillary branching may be plesiomorphic in Coleocephalocereus.