Santalales (Including Mistletoes)

Abstract

Abstract Mistletoes are flowering plants in the sandalwood order (Santalales) that parasitise tree branches. They evolved five separate times in the order and are today represented by 88 genera and nearly 1600 species. Loranthaceae ( c . 1000 species) and Viscaceae (550 species) have the highest species diversity. In South America Misodendrum (a parasite of Nothofagus ) is the first to have evolved the mistletoe habit ca. 80 million years ago. The family Amphorogynaceae is of interest because some of its members are transitional between root and stem parasites. Many mistletoes have developed mutualistic relationships with birds that act as both pollinators and seed dispersers. Although some mistletoes are serious pathogens of forest and commercial trees (e.g. Arceuthobium ), the vast majority are benign and in some cases beneficial to humans (e.g. Viscum album for anticancer drugs). Mistletoes play important roles in many forest ecosystems and their loss results in decreases in faunal diversity, thus making them keystone species. Key Concepts: A mistletoe is a branch parasite in the sandalwood order (Santalales). Mistletoes have evolved from root parasitic ancestors five times independently in five different families: Misodendraceae, Loranthaceae, Santalaceae, Amphorogynaceae and Viscaceae. The first lineage to evolve the mistletoe habit is Misodendrum , a South American parasite on southern hemisphere beech ( Nothofagus ). Most mistletoe species are found in the families Loranthaceae ( c . 1000 species) and Viscaceae (550 species). Loranthaceae evolved on the Gondwanan supercontinent and subsequently spread from Antarctica to South America, Australia, New Zealand, Asia and Africa. Many mistletoes have developed mutualistic relationships with birds that serve as both pollinators and seed dispersers. Some mistletoes such as Arceuthobium are important pathogens of forest trees, whereas most are beneficial and even keystone species in forest ecosystems.