montanum, the soil formed when these rocks weather must be subacid (pH 4.5–5.0) to (pH 3.5–4.0) to support A. bradleyi; it is slightly calcium-tolerant. It usually grows tightly wedged into horizontal or vertical crevices in exposed rock or cliff faces. These microsites are too small for most other vascular plants to survive, except for a few other spleenworts. Some mosses and lichens may occur in the same habitat. The soil there is typically composed of a mixture of acidic sand weathered from the rock and decomposing organic materials, often including old fronds. Fronds are frequently lost and decompose in summer when the soil is drier, but the crevices are usually moist or wet in winter and spring. Some shade may be present, but dense shade is not tolerated. A. bradleyi specializes in growing in this rather hostile environment, and competes poorly with other plants in even slightly richer environments. The inaccessibility of its habitat affords some protection for A. bradleyi. Quarrying and strip mining may threaten the sandstone cliffs, especially on the Cumberland Plateau. Rock climbers and botanical collectors have also damaged populations of the fern. Toxic runoff from atop cliffs can affect them, and they may also be threatened by both natural and anthropogenic shading of cliffs due to increased tree growth at the cliff base, invasive vines overrunning the cliff face, or the piling of slash against the cliff after logging. Asplenium bradleyi is protected as an endangered species in the states of Illinois, Indiana, New Jersey, and Pennsylvania, and is considered threatened in Ohio. Acadia Cliffs State Nature Preserve in Ohio, acquired in 1994, contains the state's only protected population of A. bradleyi. See also Asplenium hybrids Notes and references Notes References Works cited External links Type specimen at JSTOR Plant Science bradleyi Hybrid plants Plants described in 1873 Ferns of the United States