Habitat
Trifolium virginicum is a native clover generally distributed within the shale-barren region of Virginia, West Virginia, Maryland and Pennsylvania (Davison 1985, Keener 1970, Core 1952). Although most commonly found on shale-barrens, it is not endemic to them (Bartgis pers. comm.). Outside of barrens, T. virginicum can be found in cedar glades, dry limestone woods with thin canopies and roadside rights-of-way. There is no apparent elevational constraint within the species. Plants are found between 300 feet and 4000 feet in elevation on suitable habitat (Bartgis pers. comm.).
The term "shale barrens" 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). Local variations in associated flora may vary considerably.
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 of other species. For additional detailed information pertaining to the shale-barren community, see Dix (1990).
In Pennsylvania, Kate's mountain clover inhabits south facing, open, dry slopes of Devonian shale in the south-central portion of the state (Davison 1985). Associates include other shale barren endemics, including Senecio antennariifolius and Pseudotaenidia montana (Davison 1985), as well as Opuntia humifusa, Phlox subulata, Oenothera argillicola, Convolvulus purshianus, Antennaria virginica, Viola pedata, Plantago aristata, Penstemon hirsutus, Silene pennsylvanica, Houstonia longifolia Geranium carolinianum and Asclepias tuberosa (Duppstadt 1972, Henry 1954, Wherry 1933).
In Maryland, T. virginicum is not a true shale-barren endemic. Populations are commonly found in cedar glades, dry limestone woodlands with open canopies and similar habitats (Bartgis pers. comm.). Some populations have also been found on roadbanks. Preferred habitats include sites with a 20-30% shrub/tree cover, a south-to-west orientation and substrates of circumneutral (Braillier formation) shale (Bartgis pers. comm.). Associates on shale barrens include Convolvulus purshianus, Senecio antennariifolius and Penstemon canescens (Wherry 1929).
The shale barrens of West Virginia, composed of Devonian shale, also contain populations of T. virginicum. Associates include Eriogonum alleni, Arabis serotina, Clematis viticaulis, Oenothera argillicola, Phlox subulata, Convolvulus purshianus, Senecio antennariifolius, Deschampsia flexuosa, Campanula flexuosa, Draba ramosissima, Arabis lyrata, Houstonia tenuifolia, Penstemon canescens, Dicentra eximia, Silene pennsylvanica, Asclepias quadrifolia, A. tuberosa and Iris cristata (Artz 1948). On the outcrops of shale, T. virginicum usually grows along crevices within the harder layers of rock. Recently, populations have also been found on limestone glades within the state (Ludwig pers. comm.).
In Virginia, T. virginicum occurs on xeric, open shale slopes most frequently referred to as shale barrens (Ludwig pers. comm.). Shales are principally of Devonian and Ordovician age with exposures being primarily south or west.