Prophyll, calyculus, and perianth in Santalales

The concepts of prophyll and calyculus in Santalales are reviewed, and are found to be of variable taxonomic importance in different families. The calyculus in Loranthaceae has been generally interpreted as a reduced calyx, a concept recently challenged by Wanntorp & Ronse De Craene (2009), who concluded that it represents a fusion of prophylls. This view, as well as the accompanying biseriate corolla notion, is rejected. In Loranthaceae, prophylls associated with flowers have sometimes provided significant taxonomic features, while in Viscaceae this is true mostly in the vegetative portions of plants, especially in Arceuthobium, Dendrophthora and Phoradendron.