Viorna addisonii (Britton) Small:
United States (North America)

Clematis addisonii Britton:
United States (North America)

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Known only from the counties of Montgomery, Botetourt, Rockbridge, and Roanoke in the Ridge and Valley physiographic province of western Virginia. All but three of the populations known to be extant in 1994 are in Montgomery County. Two populations are in Botetourt County. One extant occurrence in Roanoke County. Historical occurrence in Rockbridge County.

Stems usually ascending to erect, occasionally somewhat viny, 0.6-1 m, glabrous. Leaves all simple, blade often 1-pinnate on distal and middle leaves on vigorous plants 4-13 × 2-9.5 cm; leaflets 2-6 plus additional tendril-like terminal leaflet, ovate, unlobed, 1.5-6 × 1-4.5 cm, not prominently reticulate; surfaces abaxially glabrous and glaucous. Inflorescences terminal and axillary, flowers solitary. Flowers ovoid to broadly urn-shaped; sepals purple or reddish purple, whitish toward tips, ovate-lanceolate, 1.2-2.5 cm, margins not expanded, thick, not crispate, tomentose, tips acute, spreading, abaxially glabrous. Achenes: bodies puberulent; beak 2.5-3.5 cm, plumose. 2 n = 16.

Clematis addisonii is known only from Botetourt, Montgomery, Roanoke, and Rockbridge counties in western Virginia. Reports of this infrequent species from other southeastern states have been based on misidentified specimens (W. M. Dennis 1976).

Viorna addisonii (Britton) Small

Comments: Thin soils, either on open outcrops or under light to moderate shade in mixed hardwood-juniper forests. All known sites are underlain by Elbrook Formation dolomite.

Flowering spring-early summer. Calcareous, dry woods, glades, rock outcrops; of conservation concern; 200-600 m; Va.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 21 - 80

Comments: 21 known extant occurrences as of March 1994, all in western Virginia; at least 20 populations to be gained from additional field surveys. At least 41 estimated total occurrences.

United States

Rounded National Status Rank: N2 - Imperiled

Rounded Global Status Rank: G2 - Imperiled

Reasons: Known only from 4 counties in western Virginia and restricted to areas underlain by Elbrook Formation dolomite. 21 populations are known extant (as of 1996), but more will probably be found with additional field work.

Comments: Threats from road widening projects, grazing, quarry operations. A proposed highway connecting Blacksburg with Roanoke does not directly threaten the known populations, but additional field survey work would likely locate populations that are in the corridor. Threatened by invasive plants, land-use conversion, and habitat fragmentation (Southern Appalachian Species Viability Project 2002).