Santalales (Including Mistletoes)

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.

Keywords: parasitic plant; Loranthaceae; Misodendraceae; Santalaceae; Amphorogynaceae; Viscaceae; hemiparasite; sandalwood

Figure 1.

Representatives of the five mistletoe clades. (a) Misodendrum brachystachyum (Misodendraceae), female plant with plumose, wind‐dispersed fruits (Photo courtesy of L Kelly). (b) Amyema celebica (Loranthaceae), inflorescences with showy, bird‐pollinated flowers (photo taken in the Philippines by D Nickrent). (c) Lepidoceras chilense (Santalaceae), fruiting plant (photo taken in Chile by G Amico); (d) Dendromyza ledermannii (Amphorogynaceae), a twining dendroparasite with young male flowers; inset shows closer view of fruits from a female plant (photos taken in Papua New Guinea by D Nickrent). (e) Phoradendron serotinum (Viscaceae), female plant with inflorescences (top of shoots) bearing tiny, insect‐pollinated flowers and bird‐dispersed fruits (below) (photo taken in Illinois, USA by D Nickrent).

Figure 2.

Generalised phylogenetic tree showing relationships among the component clades of Santalales (sandalwood order) based on Nickrent et al.. This tree is derived from deoxyribonucleic acid (DNA) sequences obtained from nuclear and chloroplast genes. Current evidence indicates that parasitism arose once in the order. Thick branches indicate a high degree of support for that clade. Adapted with permission from Nickrent et al..

Figure 3.

Phylogenetic tree showing relationships among genera in Amphorogynaceae and Viscaceae (from Der and Nickrent, ). The character states ‘stem’, ‘root’ and ‘dendroparasite’ were optimised on the tree using MacClade 4 (Maddison and Maddison, ) which resulted in the backbone of the tree being reconstructed as equivocal, here equated with amphiphagy, that is attaching to either roots, stems or both.

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References

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Further Reading

Calder M and Bernhardt P (1983) The Biology of Mistletoes. New York: Academic Press.

Kuijt J (1969) The Biology of Parasitic Flowering Plants. Berkeley, CA: University of California Press.

Nickrent DL and Musselman LJ (2010) Parasitic flowering plants. American Phytopathological Society APSnet Education Center, the Plant Health Instructor web publication DOI: 10.1094/PHI‐I‐2004‐0330‐01 [http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/ParasiticPlants.aspx].

Press MC and Graves JD (1995) Parasitic Plants. London: Chapman and Hall.

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How to Cite close
Nickrent, Daniel L(Mar 2011) Santalales (Including Mistletoes). In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003714.pub2]