Oenothera argillicola Mack.:
China (Asia)
United States (North America)

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Endemic to the Appalachian shale barrens of Virginia, West Virginia, Maryland and southern Pennsylvania; approximately thirty counties total.

Flowers yellow, buds erect, petals 2-4 cm, anthers 8-12 mm, ovary terete or nearly so; fruit terete, obscurely and roundly 4 angled or sulcate; stamens equal; seeds horizontal, very angular; sepal appendages separate from the base, subterminal.

Comments:

Oenothera argillicola is an endemic of the Appalachian shale barrens, occurring in the states of Virginia, West Virginia, Maryland and southern Pennsylvania (Stinson 1953).

The term "shale barren" is a general reference to certain mid-Appalachian slopes that possess the following features: 1) southern exposures, 2) slopes of 20-70 degrees and 3) a covering of lithologically hard and weather-resistant shale or siltstone fragments (Dix 1990). These barrens support a sparse, scrubby growth of Quercus ilicifolia, Q. prinus, Q. rubra, Pinus virginiana, Juniperus virginiana, Prunus alleghaniensis,, Rhus aromatica, Celtis tenuifolia, Kalmia latifolia, Bouteloua curtipendula, Andropogon scoparius, Phlox subulata var. brittonii, Silene caroliniana ssp. pensylvanica, Sedum telephoides, Antennaria spp., Aster spp., and species of Solidago (Dix 1990). Considerable variations in associated flora may occur locally.

Although adequate moisture is available for most plants within the substrata of the shale layers, adverse surface conditions act to restrict germination and establishment success of plants (Platt 1951). It is primarily the effect of high surface temperatures that limits reproductive success in these habitats. Surface soil temperatures are often well above the physiological tolerance of most plant species, reaching maximum temperatures of 63 degrees Celsius (Dix 1990). Such temperatures are high enough to cause direct damage to seedlings. For additional detailed information pertaining to the shale-barren community, see Dix (1990).

Artz (1948) stated that O. argillicola is able to exist in habitats other than shale barrens, but always requires areas with little or no competition. This inability to withstand competition may be one of the chief reasons why O. argillicola is largely restricted to shale barrens (Artz 1948). Typically, shale barren endemics are apparently obligates of high light intensity, a soil adequate for extensive root development, and a low level of competition (Platt 1951). The sparsity of plant life in the shale barrens has been explained as the result of a restriction in seedling establishment imposed by low soil moisture and high soil temperatures (Stinson 1953). Oenothera argillicola is apparently able to withstand and thrive in such conditions.

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

Estimated Number of Occurrences: 81 to >300

Comments: Unknown; approximately forty in Maryland; 100+ sites in Virginia.

Oenothera argillicola flowers in late summer, typically July through October (Gleason and Cronquist 1963).

Oenothera argillicola is unusual among eastern euoenotherids in its tendency to display only minor cytogenic aberrations typical of the subgenus, as well as its restriction to a specific habitat (Stinson 1954).

According to Stinson (1954), O. argillicola consists of: "ecologically restricted, essentially lethal-free, open-pollinated individuals with all-pairing chromosomes or small circles and several pairs. In natural populations, open-pollination should lead to considerable crossing among individuals occupying the same area. At the same time, as a result of the absence of lethals, one would expect that whenever self-pollination in the circle-bearing forms did take place segregation for chromosomes configuration would occur."

Stinson (1954) further stated that based on segmental end arrangements of chromosomes, O. argillicola is most closely related to O. hookeri of the southwestern United States. The two taxa share a number of similar features, including the presence of mostly-paired chromosomes, alethal complexes, open-pollination and ancestral end arrangements.

Morphologically, however, O. argillicola most closely resembles O. parviflora. Both show similar narrow, thick glabrous leaves, subterminal sepal tips and bent stem tips (Stinson 1954). In addition, O. parviflora is able to occupy the same shale barren habitat as O. argillicola. Based on primitive characters present in O. argillicola, Stinson (1954) surmised that it is a relict of a once widely-distributed taxon that invaded the East from its ancestral home in the Southwest. This belief was also shared by Keener (1970).

It has been suggested that O. argillicola likely played a role in the origin of O. parviflora, through crossing with ancient O. strigosa or O. biennis populations in the East (Stinson 1954).

Easily cultivated and self seeding, this species shows exceptional growth in sandy or heavy soils. Germination percentage high.

United States

Rounded National Status Rank: N3 - Vulnerable

Rounded Global Status Rank: G3 - Vulnerable

Reasons: Relatively common within its limited range, especially in Virginia. Endemic to the Appalachian shale barrens of Virginia, West Virginia, Maryland and southern Pennsylvania; approximately thirty counties total.

Global Short Term Trend: Relatively stable (=10% change)

Comments: Slightly declining due to habitat destruction, but also colonizing roadsides near shale barrens.

Comments: A significant threat to the insect pollinators of O. argillicola is presented by the spraying of Dimilin and BT insecticides for gypsy moth control. Because of the open habitat, shale barren insects are maximally exposed to pesticides (Dix 1990). Dimilin is a broad-spectrum biocide that persists until leaf fall and up to a few years in the duff and would have a long-term impact of shale-barren slopes. All insect occurrences on shale-barrens sprayed with Dimilin should be considered extirpated (Schweitzer in litt). BT is lepidopteran-specific and only persists for roughly one week (Dix 1990). Application during larval development may have devastating impacts on the fauna, however.

Five shale barrens in West Virginia and three in Virginia have been partially destroyed by road construction. Two additional barrens in Virginia were partially destroyed by railroad construction and one was crossed by a hiking trail (USFWS 1989). One barren has been destroyed through inundation caused by the damming of a stream (Dix 1990). Similar concerns have been expressed for barrens along the South Fork Valley of West Virginia where flood control measures are planned (Bartgis in litt.).

Moderately xeric sites may be subject to encroachment of exotic plant species such as Centauria maculata and a host of grass species (Dix 1990). Such encroachment may negatively impact the vigor of O. argillicola individuals. Threatened by succession due to suppression of fire (Southern Appalachian Species Viability Project 2002).

Preserve Selection and Design Considerations:

Any land acquisition effort for shale barrens and O. argillicola should take into account sufficient adjoining buffer land to adequately protect the site from outside influences, including aerial spraying for gypsy moth control.

Land protection must encompass the land needed to protect against potential impacts to O. argillicola populations and their pollinators. Shale barren habitats must be protected with sufficient buffer of scrub oak woodland or other habitat type to reduce the effects of pesticide application and other factors.

Management Requirements:

Management needs are not well understood at this time. Shale barrens may be naturally maintained due to extreme environmental conditions. Consequently, artificial habitat maintenance may not be needed. In other habitats, however, O. argillicola may benefit from active management such as canopy thinning or prescribed fire.

Management is primarily limited to exempting shale barren communities from pesticide application for gypsy moth control. Preventing application of Dimilin and BT is necessary in order to preserve the insect fauna that pollinates the species.

No active management of shale barrens appears necessary (Dix 1990). The influence of fire on barren formation and maintenance is likely negligible (Dix 1990). Fires do not typically carry through steep barrens where surfaces are bare and tree cover sparse (Platt 1951). These barrens remain open and do not require fire for opening maintenance. On barrens with shallower slopes, herbaceous cover may get relatively thick and fire may play a sole in limiting shrub succession (Thompson in litt.). Periods of severe drought may also act to eliminate shrub encroachment and reestablish the barren character (Bartgis in litt.).

Monitoring Programs:

At present, no active monitoring program is in place for O. argillicola, although all states within its range are tracking element occurrences.

Biological Research Needs:

Research needs include the identification of O. argillicola pollinators and their response and susceptibility to insecticides used to control gypsy moth infestations. Information along this line is conspicuously absent from the literature.

Basic life history information pertaining to this species is also needed, including seed germination requirements, habitat requirements and seedling survival rates.

Additional inventory work should be undertaken to determine the true status of O. argillicola.

At present, no known research is being conducted on O. argillicola.

Needs: Land acquistion efforts must encompass sufficient adjoining buffer to adequately protect the site from outside influences, including aerial spraying for gypsy moth control.

Stewardship Overview:

Monitoring should track the status of O. argillicola occurrences with respect to current management regimes, including population (flower production, seed set, pollinator abundance, seed germination, seedling establishment and/or individual survivorship) and habitat (shrub encroachment, vegetational change, etc.) maintenance. Research needs include the identification of pollinators and their susceptibility to insecticides used to control gypsy moth infestations, basic life history information pertaining to this species (including seed germination requirements, habitat requirements and seedling survival rates), and additional inventory work. Management needs are not well understood. Shale barrens may be naturally maintained due to extreme environmental conditions and artificial habitat maintenance may not be needed. In other habitats, O. argillicola may benefit from active management such as canopy thinning or prescribed fire.