Antennaria arcuata

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).

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.

Moist meadows, often on hummocks of sedges and rushes that stay drier than the surrounding areas, or at the edges of these meadows. 1500-2400 m. The wet meadows are usually surrounded by sagebrush grassland communities.

In Wyoming, Antennaria arcuata is found primarily in subirrigated meadows within broad stream channels dominated by tufted hairgrass (Deschampsia arcuata), 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).

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 Antennaria 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).

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).