Plant of the Week

Map of the United States showing states. States are colored green where the species may be found.
Range map of Agoseris aurantiaca. States are colored green where the species may be found.

Agoseris aurantiaca.
Agoseris aurantiaca from Navajo Lake Trail, Colorado. Photo © Al Schneider, www.swcoloradowildflowers.com.

Agoseris aurantiaca.
Close-up of the flower head of Agoseris aurantiaca showing the burnt-orange ligulate flowers typical of the species. Photo © Al Schneider, www.swcoloradowildflowers.com.

Agoseris aurantiaca.
Close-up of Agoseris aurantiaca from the Pasayten Wilderness, Washington. Photo © Jennifer Whipple.

Orange Mountain Dandelion (Agoseris aurantiaca)

By Walter Fertig

While it may superficially resemble the pesky common dandelion (Taraxacum officinale) the Orange mountain dandelion (Agoseris aurantiaca) is a cheerful native of mountainous areas of much of western North America. Both plants have a single large flower head terminating a leafless stalk and bleed white milky juice when the leaves or stems are broken. Its orangish-colored flowers and erect involucre bracts (the yellow flowers of dandelion are surrounded by two sets of involucre bracts, one of which is completely reflexed downwards) can distinguish orange mountain dandelion. Both species belong to the chicory tribe of the sunflower family (Asteraceae) and are characterized by flower heads consisting solely of petal-like flowers, rather than the usual mix of strap-like ray flowers and tubular disk flowers (or only disk flowers) as in other tribes within the family. Technically, these blooms are called ligulate flowers and differ from true ray flowers in having 5 lobes at the tip rather than three and in being uniformly fertile.

North America is home to 10-11 species of Agoseris, with one additional species found in South America. Traditionally, the genus name Agoseris has been translated as meaning “goat chicory”, but recently monographer Gary Baird has suggested that the correct interpretation of the Greek “agos” is “leader”. Unfortunately, Constantine Rafinesque, the eccentric 19th century naturalist who named the genus, left no clues as to his interpretation of the word. Rafinesque was infamous in his day for describing 2700 new genera of plants and animals from North America and over 6700 new species, most of which had already been named or were unworthy of taxonomic recognition. Agoseris is one of only about 30 genera he got right and that is still recognized (only around 100 of his species also survived to the present day).

There is less ambiguity about the species name “aurantiaca”, which translates as orange and describes the typical color of the ligulate flowers. These can dry to purple in age or when dried in a plant press. A pink-flowered form found in wetland habitats of the northern Rocky Mountains has been recognized as a separate species, A. lackschewitzii, but was lumped within A. aurantiaca in Baird’s 2006 revision of the genus. Individuals and populations can also vary widely in the degree of pubescence on the flower heads and stems, amount of lobing of the leaves, fruit characters, and the shape of involucre bracts. Some suggest this variability may be due to hybridization with closely related yellow-flowered Agoseris species.

Orange mountain dandelion occurs primarily in dry meadow and sagebrush habitats from the alpine zone to the foothills of mountain ranges from British Columbia and Alberta south to California, Arizona, New Mexico, and South Dakota. Disjunct populations occur in the Gaspe Penninsula of Quebec. Merritt Fernald, a leading plant taxonomist and biogeographer of the early 20th Century was intrigued by the distribution of this and other western species that occurred together in the Gaspe region but were absent elsewhere in eastern North America. Fernald attributed the unusual pattern to a refugium in the high mountains that was never overwhelmed by the great glaciers of the last Ice Age.

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