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General Description: Antennaria arcuata is a loosely white-woolly perennial herb with conspicuously arching stolons. Stolons extend up to 1 dm long and give rise to new plants. Plants are dioecious (either staminate or pistillate). Basal leaves are few, wider at the top, and several cm long. Flowering stems are solitary, 3 to 4 dm tall, with well-developed, and gradually reduced stem leaves. The flower heads are moderately numerous and arranged in a close terminal cluster. Male and female plants vary slightly in size of flowers, involucre (bracts at base of flower head), and pappus (modified calyx on top of ovary/fruit) (Lorain 1990).
Technical Description: Plants white-wooly, perennial, spreading by means of conspicuously arching stolons about 1 dm long or less, the stolons rooting at the end and giving rise to another short-lived plant with a single strict flowering stem 3 - 4 dm tall; basal leaves oblanceolate, several cm long, but few and not persistent; cauline leaves narrow, but well developed, moderately numerous, gradually reduced upwards; heads rather many in a close terminal cluster; involucre about 5 mm high, tomentose below, the bracts whitish and minutely striate above; pappus bristles only slightly irregularly united at the base (Cronquist 1950).
Diagnostic Characteristics: The most distinctive feature of Antennaria arcuata is its conspicuously arching, woolly stolons (hence its common name). This feature is diagnostic. Other characters to look for are the single flowering stem, white-woolly pubescence, and preference for damp meadow habitats.
Infraspecific Taxa: There are no infraspecific taxa for Antennaria arcuata.
Similar-appearing Taxa: A distinctive and diagnostic feature of Antennaria arcuata is its conspicuously arching, woolly stolons. This species is quite distinct from any other species of Antennaria in the western United States. The congener A. microphylla is sympatric at the one known Idaho population and can be differentiated by its mat-forming habit and conspicuous tuft of small basal leaves. Additionally, A. microphylla tends to grow in slightly drier habitats. Antennaria flagellaris is a short-lived perennial that forms filiform stolons, but is less than 1 dm tall, occurs on dry, rocky sites and should not be mistaken for A. arcuata. Antennaria arcuata can be confused with Gnaphalium chilense (cudweed), which grows in the same habitat and also has a white-woolly pubescence, but is an annual or biennial and lacks stolons.
Identification of this Taxon in Idaho: The conspicuously arching, wooly stolons are distinctive and serve as a ready feature for field identification.
Global Comments: A distinct species.
Idaho Comments: See Global comments.
Global: Antennaria arcuata is a regional endemic restricted to three disjunct areas of central Wyoming, northeastern Nevada, and south-central Idaho. Rangewide, the species is known from 25 - 26 occurrences. Twenty are found in Fremont County, Wyoming, one in Idaho, and the remainder in Nevada. All Wyoming populations occur wholly or in part on BLM lands. One occurrence is protected within The Nature Conservancy's Sweetwater River Preserve. Nevada populations occur on private and Humboldt National Forest land. The single Idaho population is located on private land and supports several thousand individuals (Lorain 1990). When last visited in 1989, the Idaho population near Carey contained about the same number of plants as reported in 1985.
Wyoming surveys in 1995, found an estimated 99,00 - 130,000 individuals. Compared with estimates made in 1982, total population numbers appear to be stable or slightly decreasing. Populations range in size from 200 to approximately 30,000 individuals. Populations consist of widely scattered, but often dense clusters of unisexual "clones" of flowering and vegetative plants. In demographic plots, total density ranged from 38 - 105 plants per square meter, and vegetative rosettes typically outnumber flowering plants by a factor of 5:1 or greater (Fertig 1996).
Exclosure studies suggests A. arcuata can decline or be eliminated in habitats where graminoid cover becomes very dense and soils become too mesic. Throughout its range, livestock grazing continues to be the dominant land-use practice. Under appropriate stocking rates, grazing meadow habitats may benefit the A. arcuata by keeping competing graminoid and shrub cover short (Fertig 1996). The restricted habitat of A. arcuata make this species vulnerable to habitat degradation or loss. The primary real or potential threats to this species are trampling by congregated livestock and vehicles, water developments altering local hydrologic regimes, plowing and reseeding its meadow habitat to hayfields, disturbances associated with mineral exploration and development, and competition from introduced and native weeds. Status surveys for A. arcuata were compiled in 1979 (Packard 1979) and 1980 (Atwood 1980), before much information was known about the species. Comprehensive status surveys have been completed for Idaho (Lorain 1990), and more recently for central Wyoming (Fertig 1996).
Antennaria arcuata had been under consideration for federal listing under the Endangered Species Act from 1975 to 1996. Based on the absence of significant downward population trends, and survey work completed in Wyoming, where most populations are known, A. arcuata was not recommended for federal listing (Fertig 1996).
In Wyoming, A. arcuata is listed as a Special Status plant species by the BLM Rock Springs District, and has been recommended for state-wide BLM Sensitive status by the Wyoming Natural Diversity Database (Fertig 1996). Antennaria arcuata is on the provisional Nevada BLM Sensitive Species list. It has also been recommended for addition to the Idaho BLM Sensitive Species list (Lorain 1990). Antennaria arcuata has a global conservation rank of G2, indicating it is globally imperiled because of rarity or other factors making it vulnerable to extinction. Antennaria arcuata is ranked S2 in Wyoming. It is ranked S1 in Idaho and Nevada, indicating it is critically imperiled in these two states because of rarity or some other factor making it vulnerable to extinction.
Idaho:Antennaria arcuata is on the Idaho Native Plant Society's list of globally rare plant taxa where it has a priority of 5, indicating that in Idaho, the species faces high magnitude, non-imminent threats. It has a Conservation Data Center rank of S1, indicating the species is critically imperiled in Idaho because of extreme rarity or because of some factor of its biology making it especially vulnerable to extinction.
Global: Antennaria arcuata is a regional endemic found in three disjunct areas in south-central Idaho, northeastern Nevada, and central Wyoming (Bayer 1992).
Idaho: In Idaho, Antennaria arcuata is known only from Huff Creek Meadows, near Carey, Blaine County, in the south-central part of the state.
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| Antennaria arcuata habitat |
Elevation (Global): 4950 feet to 7900 feet.
Elevation (Idaho): 4950 feet.
Global: In Wyoming, Antennaria arcuata is found primarily in subirrigated meadows within broad stream channels dominated by tufted hairgrass (Deschampsia cespitosa), Baltic rush (Juncus balticus), Kentucky bluegrass (Poa pratensis), Nevada bluegrass (Poa nevadensis), Junegrass (Koeleria macrantha), and clustered field sedge (Carex praegracilis). These communities are often found in a matrix of silver sagebrush (Artemisia cana) and shrubby cinquefoil (Potentilla fruticosa). Within these communities, A. arcuata is most commonly associated with hummocky topography, but it also occurs on level ground, or shallow depressions. Soils tend to be alkaline, clayey, and high in organic matter. At higher elevations in the South Pass area, it may be found at the edge of silver sagebrush stands and willow thickets in subirrigated meadows of tufted hairgrass, Baltic rush, spike-rush (Eleocharis sp.), and meadow barley (Hordeum brachyantherum). Antennaria arcuata is notably absent from riparian sites with tall, dense graminoid or shrub cover, and where soils are saturated. It is also absent from the dry, gravelly big sagebrush (Artemisia tridentata) grassland ridges bordering the meadow habitats (Fertig 1996).
The one Idaho population occupies a mesic natural grass-sedge meadow surrounded by sagebrush-steppe (Lorain 1990). Nevada populations are found in open, flat meadows that are not permanently wet (Mozingo and Williams 1980).
Idaho: At the one Idaho population, A. arcuata occurs on small, bare or lichen-covered spots of soil within a moist, grass-sedge-dominated meadow. The meadow is surrounded by sagebrush-steppe vegetation (Lorain 1990).
Global: Antennaria arcuata appears to decrease in areas with tall or dense vegetation cover. Colonies within BLM exclosures have declined or been locally extirpated where grazing has been prevented and the vegetation notably denser and taller. High vegetation cover may also promote greater water retention in the soil, creating microsites too wet for A. arcuata. Several Wyoming colonies have also declined over time where shrubs have replaced the graminoid plant community. In Wyoming, A. arcuata is often found with A. microphylla in hummocky habitats. Antennaria microphylla generally replaces A. arcuata on drier hummock tops and on wetter soil sites. Changes in soil moisture retention capacity, either through increased vegetation density or soil compaction, may favor A. microphylla at many sites (Fertig 1996).
Idaho: The Idaho population occurs in a meadow that is seasonally moist to wet in the spring, and can receive considerable snow accumulations during the winter with the possibility of frost heaving. This population is located between a thermal spring and cold water channel, which feed into the meadow. It is unknown if the mixing of these waters is an important ecological factor. Plants tend to be associated with small, bare soil sites within the graminoid-dominated meadow in places lacking much other vegetation cover.
Global: Antennaria arcuata is a perennial that reproduces vegetatively by spreading stolons, or sexually by seed. Although many species of Antennaria also reproduce asexually by apomixis (the production of viable seed without fertilization or meiosis), there is no evidence of this in A. arcuata (Bayer 1984). Chromosome counts and demographic analysis of Wyoming and Nevada populations have shown this species to be a diploid, with populations containing approximately equal proportions of staminate and pistillate individuals (Bayer 1992). Mature, presumably viable fruits were commonly observed in Wyoming populations. On average, pistillate plants contained 10 - 12 heads per flowering stem, and 20 fruits per head (Fertig 1996). The one Idaho population is reported to be comprised of only pistillate plants (Lorain 1990). This needs further investigation. Known apomictic species of Antennaria are polyploids with populations consisting almost entirely of pistillate plants (Bayer 1984).
Bayer (1992) found the amount of genetic diversity within populations of A. arcuata to be much lower than other narrowly endemic, or wide-ranging sexual species of Antennaria. Due to inbreeding within populations and low gene flow between populations, Bayer also reports small, but meaningful differences in the genetic structure of six A. arcuata occurrences in Nevada, Idaho, and Wyoming. These observations support the contention that populations have been isolated from each other for a relatively long time (Bayer 1992).
Possible hybridization or introgression between A. arcuata and A. microphylla has been reported from one Wyoming occurrence (Bayer 1992). Unlike polyploid species in Antennaria, hybridization appears to be uncommon among the diploid taxa of the genus (Cronquist 1994).
Idaho: See Global Reproduction comments.
Phenology (Idaho): Flowering takes place in late June and continues through August in Idaho. Fruits develop in August and September.
Global: The Idaho population of Antennaria arcuata occurs on private land. There have been no systematic surveys done for this species in Idaho since the late 1980's. It has also been recommended for addition to the Idaho BLM Sensitive Species list because of the close proximity of the known population to BLM land (Lorain 1990).
No new populations have been discovered in recent years in Nevada despite occasional survey work. Populations are known from private and Humboldt National Forest lands. Antennaria arcuata is on the Humboldt National Forest's Sensitive Species list (Anderson 1991), and is also on the provisional Nevada BLM Sensitive Species list. These designations confer some special management considerations for the species on public lands. However, there are no studies or special management activities presently in place for the Nevada populations.
In Wyoming, the BLM Lander Resource Area began a long-term monitoring study of the effects of grazing on A. arcuata in 1983 (Marriott 1986). Two one-acre, livestock-proof exclosures were established to determine plant production and frequency. Examination of the sites in 1995 found A. arcuata outside, but not inside the exclosure. A number of recommendations have been made for the Wyoming populations. Development needs to be carefully regulated on BLM sites containing A. arcuata to prevent damage from water development projects, road construction, recreational activity, and mineral exploration and development.
In Wyoming, A. arcuata is listed as a Special Status plant species by the BLM Rock Springs District, and has been recommended for state-wide BLM Sensitive status by the Wyoming Natural Diversity Database (Fertig 1996).
Idaho: The one known population of A. arcuata in Idaho is located on private land. The area is used for grazing livestock. Lorain (1990) comments that existing land usage appeared to be compatible with the species long-term viability at the site. She noted there are no known past, existing, or potential threats related to disease or predation, and that livestock grazing poses no significant threat at the current time. Indirect activities associated with livestock grazing, such as stockpond construction or other water developments do represent a potential threat, however. Other identified potential threats include the invasion of weedy species, and if ever proposed, widening or other alterations to Highway 93, which passes near the population.
Lorain (1990) made several recommendations in her status survey report for A. arcuata. These included: (1) Establish a monitoring program to study the long-term effects of livestock grazing on the species. (2) Study the hydrologic relationship between the thermal and cold springs, and A. arcuata. (3) Conduct additional inventories in areas with suitable habitat. (4) Add A. arcuata to the BLM state sensitive species list, as it is known to occur within approximately 0.25 mile of BLM land.
At one time, a Preserve Design Package was prepared and the Huff Creek Meadow site was considered a priority acquisition by the Idaho field office of The Nature Conservancy. This purchase was never consummated, however.
General Comments (Idaho): There have been numerous searches of potentially suitable habitat in the vicinity of the known Idaho occurrence, but no new discoveries have been made (Caicco 1986).
Inventory Needs (Idaho): The Duck Valley Indian Reservation area in southwestern Idaho is not too far from the location of the Nevada populations and may contain some areas of potentially suitable habitat.
Anderson, S., M. White, and D. Atwood. 1991. Humboldt National Forest sensitive plant field guide. USDA Forest Service, Intermountain Regional Office, Ogden, UT. Not paged.
Atwood, D. 1980. Status report on Antennaria arcuata. U. S. Forest Service, Ogden, UT. Not paged.
Bayer, F. J. 1992. Allozyme variation, genecology, and phytogeography of Antennaria arcuata (Asteraceae), a rare species from the Great Basin and Red Desert with small disjunct populations. American Journal of Botany 79(8): 872-881.
Cronquist, A. 1950. Notes on the Compositae of the northwestern United States. Leaflets of Western Botany 6(2): 41-56.
Cronquist, A., A. H. Holmgren, N. H. Holmgren, N. H. Holmgren, J. L. Reveal, and P. K. Holmgren. 1994. Intermountain flora: Vascular plants of the Intermountain West, U.S.A. Volume 5. New York Botanical Garden, N.Y. 496 pp.
Fertig, W. 1996. Status report on Antennaria arcuata in central Wyoming. Cooperative Agreement # K910-A4-0011, Task Order # 007. Prepared for the Bureau of Land Management, Wyoming State Office, Rawlins District, and Rock Springs District. Wyoming Natural Diversity Database, Laramie, WY. 34 pp. plus appendices.
Lorain, C. C. 1990. Report on the conservation status of Antennaria arcuata in Idaho. Prepared for Idaho Department of Parks and Recreation. Idaho Department of Fish and Game, Conservation Data Center, Boise. 42 pp. plus appendices.
Marriott, H. 1986. Status report for Antennaria arcuata. Prepared for The Nature Conservancy, Rocky Mountain Heritage Task Force, Boulder, CO. 42 pp. plus appendices.
Mozingo, H. N., and M. Williams. 1980. Threatened and endangered plants of Nevada. U. S. Fish and Wildlife Service, Portland, OR; U.S. Department of the Interior, Bureau of Land Management, Reno, NV. 268 pp.
Packard, P. L. 1979. Status report for Antennaria arcuata. The College of Idaho, Caldwell. 7 pp.
AUTHOR: M. Mancuso
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