Language selection

Government of Canada / Gouvernement du Canada

Search

Parasitic plants

There are hundreds of species of plants that are parasitic on other plants. As parasites, these plants extract nutrients, carbohydrates, and/or water from their hosts. The degree of parasitism depends on the species. Parasitism occurs as these plants connect to their hosts’ roots, stems, or branches. Some, such as dodder (Cuscuta spp.), broom rape (Orobanche spp.), and witchweed (Striga spp.), are important in agricultural production where they parasitize various crops. Plants that are parasitic to trees, limited to the order Santalales (sandalwoods), predominantly occur in the tropics or sub-tropics, with fewer species found in temperate regions. Mistletoes are probably the best-known group of parasitic plants, with European mistletoe (Viscum album) and American mistletoe (Phoradendron leucarpum) associated with Christmas traditions as two representative species. The distribution of Phoradendron does not extend into Canada. In Canada, it is the dwarf mistletoes (Arceuthobium) that damage a variety of conifer tree species. Dwarf mistletoes are obligate parasites (they require a host to survive and reproduce), diminutive in size, with greatly reduced leaves, and lacking a root system. They obtain nutrients, carbohydrates, and water through vascular connections with the host. Globally, there are 29 recognized species of dwarf mistletoes, and most species are found in southwestern North America.

This database includes species from only one family within the order Santalales. Taxonomists currently debate the classification of the Viscaceae, traditionally including genera such as Arceuthobium, Phoradendron, and Viscum. Some researchers have reduced Viscaceae to a subfamily within the larger family Santalaceae. We continue to use the term “Viscaceae,” however, until further data prompt a revision. Species listed in the family Viscaceae below are linked to the site’s pest fact sheets.

Order Santalales

The Santalales are angiosperms with an almost global distribution that consist of 18 families, about 175 genera, and more than 2,400 species. There are both nonparasitic and parasitic flowering plants in this order.

Family Viscaceae

This family consists of stem-parasitic flowering herbs and shrubs commonly referred to as mistletoes. There are seven genera and more than 500 species in this family. Species may be dioecious (e.g., Arceuthobium), monecious, or andromonoecious. Flowers are small, usually less than 3 millimetres, and unisexual, bearing 2–4 petals. Leaves are opposite, persistent, and either developed or reduced to scales (e.g., Arceuthobium). Leaves and stems are usually brittle, and either hairless (glabous) or hairy (pubescent). The fruit is a berry with a fibrous mesocarp and containing a single endospermous seed with attachment structures (viscin) to adhere to the host. The seed’s endosperm contains chlorophyl (chlorophyllous).