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Paintbrush: The Prettiest Parasite On The Prairie?

Indian paintrbrush (Castilleja linariifolia) in Grand Teton National Park.
Indian paintrbrush (Castilleja linariifolia) in Grand Teton National Park.

Most people are familiar with the showy red or yellow flowers of the Indian paintbrushes. They can be found from the dry valley grasslands to lush alpine meadows. There are 21 species of the paintbrush just in Montana, including bristly paintbrush, the red-flowered species of dry slopes and scarlet paintbrush which is common in meadows and along streams.

During drought years you may be able to notice that while most of the plants on the hillside will look dry and withered by the early summer, paintbrushes remain healthy-looking. Do these delicate plants have a more efficient way of obtaining water than their neighbors?

The answer is yes. Paintbrushes and their close relatives, louseworts and owl clovers are hemiparasites; that is, they obtain part of their water and nutrients from neighboring plants. When a paintbrush root comes in contact with those of another plant, it forms a short side branch that then penetrates the neighbor’s root. Paintbrushes lose water to the atmosphere more easily than other plants. This, as the the sun and wind draw water from the paintbrush plant, a kind of suction is created that causes water and sap to be drawn from the roots of the host plant into the roots and foliage of the parasite.

Researchers have determined that paintbrushes and their relatives obtain water, mineral nutrients such as nitrogen and phosphorus, and carbon compounds such as sugars and amino acids from their hosts. Paintbrushes are not host-specific, and a variety of plants, including other paintbrushes, may be used by the same species.

Paintbrushes and their relatives have green leaves and are able, to some extent, to synthesize their own carbon compounds and obtain their own water and nutrients. Although most species of paintbrush can flower and produce seed in the greenhouse, garden, or other benign environment, a host is usually necessary for survival in the more stressful and competitive conditions occurring in native plant communities.

Although the effects on host plants have not been studied, dense colonies of paintbrush undoubtedly have an impact on the vegetation. Next time you see one of these beautiful plants, perhaps it will make you think of the complex interactions occurring underground.

"Field Notes" is produced by the Montana Natural History Center.

(Broadcast: "Fieldnotes," 08/25/15. Listen on air or online Sundays at 12:55 p.m., Tuesdays at 4:54 p.m., and Fridays at 4:54 p.m., or via podcast.)

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