Packera cana (Hook.) W.A. Weber & A. Love
Basis for Listing
Packera cana (gray ragwort) is widespread and abundant in semi-arid regions of the western United States and Canada. Occurrences become less common going eastward into the Great Plains and end rather abruptly near the North Dakota/Minnesota border (Barkley 1980). The most likely explanation is the gradual climatic change from dry to moist conditions going from west to east. There are very few places in Minnesota that provide the dry grassland habitat required by this species. Most suitable habitats in Minnesota are found in native grasslands in isolated pockets of sandy and gravelly soil in the northwestern counties (Aspen Parklands Subsection). These places are also desirable places to mine for aggregate materials, which is the main threat to this species and its habitat. The number of known occurrences in Minnesota is fewer than a dozen and most consist of only a few plants. For these reasons, P. cana was listed as an endangered species in Minnesota in 1996.
Packera cana is a cespitose perennial with a felt-like covering of short grayish white hairs (tomentum). The stems are erect, or nearly so, usually about 30 cm (12 in.) tall. The leaves are found on the length of the stem as well as the base of the stem. They are 2-12 cm (0.8-4.7 in.) long and 1-2 cm (0.4-0.8 in.) wide with entire margins and rounded tips. The flowers are yellow, in heads up to 2.5 cm (1.0 in.) across; the heads are arranged in cymes. Fruits are hairless, ribbed achenes (Greenman 1917).
Packera cana appears sporadically and locally in the northern plains. In Minnesota, it is found on the upper slopes of hills in dry prairie remnants in sandy or gravelly soil. Associated species include Gaillardia aristata (blanketflower), Oenothera suffrutescens (scarlet gaura), Orobanche fasciculata (clustered broomrape), and Penstemon albidus (white beard tongue).
Biology / Life History
Packera cana is an insect-pollinated perennial. Specific pollinators have not been identified, but the structure of the flower indicates it is likely pollinated by a variety of common flying insects. Reproduction is entirely by seeds, which are spread short distances by wind and possibly by small ground-foraging animals. The habitat of P. cana is characterized by extremely droughty soils, which indicates it will be little harmed by periodic droughts. In fact, droughts may give it a competitive advantage over prairie species not so well able to survive extreme water stress.
Conservation / Management
Gravel quarrying is a serious threat to the habitat of P. cana. It is virtually impossible to extract gravel without completely destroying the prairie habitat. Overgrazing can also pose a threat, though the plants may be able to survive low-intensity livestock grazing for a limited period of time. Prescribed burning may be useful in managing the habitat of this species but should be limited to early spring before plants have emerged from the ground. Invasive species such as Centaurea stoebe ssp. micranthos (spotted knapweed) also pose a potential threat and should be carefully monitored.
Best Time to Search
The best time to search for Packera cana is when it is in flower, from mid-May through June.
Welby R. Smith (MNDNR), 2020
(Note: all content ©MNDNR)
References and Additional Information
Barkley, T. M. 1980. Taxonomic notes on Senecio tomentosus and its allies (Asteraceae). Brittonia 32(3):291-308.
Greenman, J. M. 1917. Monograph of the North and Central American species of the genus Senecio. Part II. Annals of the Missouri Botanical Garden 4(1):15-36.
Rickett, H. W. 1999. Wildflowers of the United States. Volume 6, Part 3, Central Mountains and Plains. McGraw-Hill, New York, New York.
Trock, D. K. 2006. Packera. Pages 570-602 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 20. Oxford University Press, New York, New York.
Vance, F. R., J. R. Jowsey, J. S. McLean, and F.A. Switzer. 1984. Wildflowers of the Northern Great Plains. University of Minnesota Press, Minneapolis, Minnesota. 382 pp.