Roan Mountain Bluet
Roan Mountain Bluet
Hedyotis purpurea var. montana
|Listed||April 5, 1990|
|Description||Low-growing perennial with clusters of bright purple flowers.|
|Habitat||Steep mountaintop slopes and cliffs.|
|Threats||Hikers, recreational and residential development.|
|Range||North Carolina, Tennessee|
The Roan Mountain bluet is a low-growing perennial with square, narrowly winged stems, which form loose tufts 4 in (10 cm) to 6 in (15 cm) tall. The untoothed leaves are arranged in opposite pairs. Terminal clusters of bright, four-petaled, purple flowers appear in July and early August. This variety is easily distinguished from other bluets by its relatively large reddish purple flowers, relatively small sessile ovate leaves, compact stature and clump-forming growth habit, and its exposed mountaintop habitat. The species has also been known by the names Houstonia montana and H. purpurea var. montana.
The four main flower visitors, listed in decreasing order of probable pollination effectiveness, were small staphylinid beetles, bumblebees, syrphid flies, and ants. A field experiment showed that hand-pollination, using mixed pollen donors, could not boost the percentage of seeds set above the 50% level achieved by natural pollinator activity. The hand-pollination study also provided insight into the breeding system and genetic integrity of the Roan Mountain study population. Plants of both heterostyly morphs did not set seeds when self-pollinated but did set normal levels of seeds when cross-pollinated with pollen from the opposite morph. This suggests that this population of Roan Mountain bluet is self-incompatible, as is expected in a heterostylous breeding system. Moreover, plants that were hand-pollinated, using neighboring pollen donors, set seeds just as well as naturally pollinated plants and just as well as plants that were hand-pollinated using distant, presumably unrelated, pollen donors. Inbreeding depression was not evident in the study population.
Asexual propagation occurs in late summer when Roan Mountain bluets begin to produce basal rosettes from rhizome buds. Field observations revealed some evidence of fungal pathogens and vertebrate grazing in the study population during late summer.
Roan Mountain bluet is endemic to mountaintop sites in western North Carolina and eastern Tennessee. It is an early successional plant that grows in shallow, acidic soils on sunny slopes, cliffs, and rock outcrops.
The plants typically grow in gravel-filled pockets found on northor northwest-facing cliff ledges or on talus slopes associated with outcrop exposures on the south or southwest slopes of mountain balds. Winter freezes and thaws can chum gravelly substrates, potentially burying or exposing seeds, dislodging rooted plants, and exposing new substrate for recolonization. During the growing season, these sites are often bathed by water condensing from up-welling air, frequent mountain fogs, passing mid-elevation clouds, or summer thunderstorms. Although outcrop soils are relatively high in organic matter compared to typical mineral soils, they are still shallow. Therefore, once moist conditions pass, the soils drain rapidly and dry out within two to three days.
Plants growing on most cliff sites receive direct sunlight for less than half the day. In comparing presence versus absence data, it was found a correlation between relatively low levels of solar radiation and the presence of Roan Mountain bluet (potential solar radiation decreases with an increasing north aspect and slope steepness). Plants growing on the talus slopes of balds potentially receive more hours of direct light, but their lower leaves are often shaded by neighboring forbs. Frequent fog and clouds further reduce the amount of light the plants receive during the growing season. Surface temperatures are moderated throughout the year by winds and the thermal mass of rock outcroppings.
Associated species include sand myrtle, Catawba rhododendron, asters, sedges, goldenrod, alumroot, mountain saxifrage, and various grasses. On some sites it occurs along with spreading avens, which is federally listed as endangered. It is also found with Heller's blazing star, which are listed as threatened. Surrounding coniferous forest is dominated by red spruce and Fraser fir, a candidate for federal listing.
Within the past few years, the existence of eight populations of Roan Mountain bluet have been documented, all on mountain peaks in northwestern North Carolina (Ashe, Avery, Watauga, and Mitchell Counties). An additional population was last observed in 1980 at a site in Yancey County, North Carolina, but the population has not been re-confirmed since then, despite several search efforts, and is now presumed to be extirpated. The cause of this extirpation is not clear but probably reflects a combination of successional change, small population size, and trampling by hikers. The Tennessee portion of the Roan Mountain population also may now be extirpated.
Most of the populations are spread among cliff ledges that are difficult to census without climbing gear. Current estimates of population size are based on crude visual estimates of the numbers of plant clumps found in accessible portions of these populations.
Each of the three largest populations— Grandfather Mountain, Roan Mountain, and Bluff Mountain—reportedly contains 1,000 or more plant clumps. However, these populations are highly fragmented, and individual colonies within each population rarely contain more than 250 clumps. Each of the five smallest populations— Three Top Mountain, Paddy Mountain, Phoenix Mountain, Rich Mountain, and Hanging Rock— probably contains less than 100 plant clumps. Populations have not been counted or mapped until recently; therefore, it is not known if the populations are maintaining themselves.
Two populations of Roan Mountain bluet are found at the juncture of Avery and Watauga Counties, North Carolina; one is at the boundary of Mitchell and Avery Counties, North Carolina, and Carter County, Tennessee; two are in Ashe County, North Carolina, and one is in Watauga County, North Carolina.
The surviving populations are small and vulnerable. One site located on Forest Service land contains 41% of the known species population.
Roan Mountain bluet populations may be better described as metapopulations; each population consists of a series of discrete subpopulations isolated from each other by 328.1 ft (100 m) to several kilometers of intervening habitat. It is unknown whether these subpopulations survive indefinitely; each may be threatened either because of natural biological processes, such as successional encroachment by native plants or the local build-up of pathogens or herbivores, or because of vegetational destruction caused by severe weather conditions such as freeze/thaw cycles, downpour-induced landslides, or lighteningignited fires.
The main threats to the Roan Mountain bluet are habitat disturbance by hikers and recreational and residential development. The largest remaining population is on public land heavily used by hikers, rock climbers, and sightseers. Two populations are on sites that have been developed for commercial recreation. The construction of roads, trails, and parking lots threatens the remaining populations. The presence of Roan Mountain bluet needs to be taken into account when construction is planned.
Roan Mountain bluet faces additional long-term threats from natural processes. As an early successional plant, it is susceptible to invasion by shrubs and trees, which would shade out the remaining populations. In addition, the surrounding high elevation forest is suffering a drastic decline caused by air pollution and the invasion of an exotic insect, the balsam woolly aphid. The loss of these forests might allow the habitat to become too arid to support healthy, reproducing Roan Mountain bluet populations.
Conservation and Recovery
In North Carolina, the Natural Heritage Program, the North Carolina chapter of the Nature Conservancy, and the U.S. Fish and Wildlife Service are working with landowners to protect and manage Roan Mountain bluet sites. The Nature Conservancy owns part of one cliff-side site and is monitoring and protecting its populations by limiting public visitation. The U.S. Forest Service owns the Roan Mountain site and the historic Big Bald site, and is trying to protect the species by placing new recreational facilities away from known locations and by creating innocuous natural barriers to discourage access and trampling at heavily used locations. Unfortunately, these barriers have not proven particularly effective in alleviating visitor impacts at scenic public recreation areas where the Roan Mountain bluet grows.
Fortunately, current landowners support conservation efforts at all three large sites. Potential recovery success is highest for the Roan Mountain population, found entirely on national forest lands. Federal law mandates protection of this population, and cooperation has been established with the U.S. Forest Service. Potential recovery success is also high for the Grandfather Mountain population. Much of this population is in remote or inaccessible areas, and the private landowner has shown a serious conservation commitment by donating a conservation easement that protects much of the bluet's habitat. He has also rerouted visitor traffic at one popular location to protect two other federally threatened plant species. Recovery efforts are also promising for the third large population—the Nature Conservancy's Bluff Mountain Nature Preserve. However, most of this population is on steep cliff sides, just beyond the preserve's property boundaries, and will require further work.
The North Carolina Arboretum in Asheville recently became an allied facility of the Center for Plant Conservation. They have proposed to serve as the seed-storage and plant-propagation facility for Roan Mountain bluet and have established a collection of specimens in cooperation with the North Carolina Plant Conservation Program.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
Massey, J., P. Whitson, and T. Atkinson. 1980. "Endangered and Threatened Plant Survey of Twelve Species in the Eastern Part of Region Four." U.S. Fish and Wildlife Service.
U. S. Fish and Wildlife Service. May 13, 1996. "Recovery Plan for Roan Mountain Bluet." U. S. Fish and Wildlife Service, 46 pp.
"Roan Mountain Bluet." Beacham's Guide to the Endangered Species of North America. . Encyclopedia.com. (January 22, 2019). https://www.encyclopedia.com/environment/science-magazines/roan-mountain-bluet
"Roan Mountain Bluet." Beacham's Guide to the Endangered Species of North America. . Retrieved January 22, 2019 from Encyclopedia.com: https://www.encyclopedia.com/environment/science-magazines/roan-mountain-bluet
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