Family: Asteraceae (A Utah Flora - Compositae) - Sunflower Family
Biennial or perennial spiny herbs; stem juice is watery. There are at least 5 species of Cirsium at Arches National Park: Cirsium calcareum (Cainville thistle) is a perennial herb; Cirsium neomexicanum var. neomexicanum (New Mexico thistle) is a biennial herb from taproots; Cirsium rydbergii (Rydberg's thistle) is a perennial herb; Cirsium undulatum var. undulatum (Gray thistle/Wavyleaf thistle) is a perennial herb; Cirsium vulgare (Bull thistle – non-native) is a biennial herb from taproots
Leaves: alternate and basal; pinnatifid simple; most are spine-tipped
Flowers: Pink, purple, red, or white disk flowers – no rays; flower head appears to be a single flower, but is composed of several flowers (a composite). Perfect or imperfect.
Corollas of Cirsium calcareum are pink to pink blue and 1” to 1.32” (25 to 33 mm) long; Corollas of Cirsium neomexicanum var. neomexicanum are cream or white and are 0.6” to 1.32” (15 to 33 mm) long; Corollas of Cirsium rydbergii are pink and are 0.76” to 1.12” (19 to 28 mm) long; Corollas of Cirsium undulatum var. undulatum are pink, pink purple, or creamy white and are 0.88” to 1.16” (22 to 29 mm) long; Corollas of Cirsium vulgare are rose to purple and are 1” to 1.4” (25 to 35 mm) long
Pollinators: Cirsium undulatum and Cirsium vulgare are pollinated by bees, flies, moths, butterflies, beetles and self-fertile; some Cirsium species are pollinated by hummingbirds
Fruits: achene – 1 seeded with hard shell
Blooms in Arches National Park: May, June
Habitat in Arches National Park: hanging gardens, riparian, disturbed areas, desert shrub and pinyon-juniper communities
Location seen: Cirsium undulatum: Park road near Park Avenue, park road near Salt Valley road
Other: The genus name, “Cirsium”, is from the Greek “kirsion” meaning “swollen vein” because one species was used to treat swollen veins. The species name, “calcareum”, means “chalky white, or growing on chalky soil”; the species name, “neomexicanum”, means “of or from New Mexico” referring to the plant's range; the species name, “rydbergii”, honors Per Axel Rydberg (1860-1931), a plant taxonomist and the first curator of The New York Botanical Garden Herbarium whose specialty was the flora of the Rocky Mountains and Great Plains areas; the species name, “undulatum”, means “wavy” referring to the plant's leaves; and the species name, “vulgare”, means “common”.
Cirsium rydbergii is a C3 federal species of concern. C3 are taxa that are no longer being considered for listing as threatened or endangered species by the United States Fish and Wildlife Service. Although this C3 candidate is no longer officially considered for listing under the Endangered Species Act, the former candidate status is important historical information.
This family is the most advanced and complex of the dicots. The family is rich in oils and resins and is found in every part of the world, but is infrequent in the tropical rainforest. Aquatic or semi-aquatic species are also uncommon.