Studies indicate that the present population of Bradley's spleenwort arose from several independent doublings of sterile diploid hybrids.

While A. bradleyi is easily outcompeted by other plants in more fertile habitats, it is well adapted to the thin, acidic soil and harsh environment of its native cliffs, where it finds few competitors.

[6] Its rhizomes (underground stems) are short and parallel to the ground, or sometimes curving upwards, so the fronds spring up in a cluster.

The rhizome is about 1 millimeter (0.04 in) in diameter, covered with narrowly triangular scales that are dark reddish to brown[2] and strongly clathrate (bearing a lattice-like pattern).

Small brown scales at the base of the stipe diminish to hairs as one moves towards the tip of the leaf.

The blade is cut into 5 to 15 pairs of pinnae (possibly as low as 3 or as high as 20 in unusual specimens), which are themselves deeply lobed or further subdivided into pinnules.

Specimens found growing in a very shaded environment, which lacked color in the rachis and were simply pinnate, have been mistaken for green spleenwort (A. viride).

[4] A dwarfed form of A. bradleyi, with fronds about 1 centimeter (0.4 in) long, was discovered in Illinois by Wallace R. Weber and Robert H. Mohlenbrock.

× wherryi, the dark color of the stipe again ends at the base of the leaf blade, the overall shape of the blade tends to be more distinctly lance-shaped, and the fronds are somewhat more deeply cut than A. bradleyi, progressing from bipinnate in the lower half to pinnate-pinnatifid and finally pinnate at the apex.

On close examination, its spores are found to be abortive, and the sori are smaller and not do not become fused with each other as they grow, as they do in fertile A. bradleyi.

[15] The scientific discovery of A. bradleyi occurred in 1871, when Frank Howe Bradley collected a number of specimens near Coal Creek, on Walden's Ridge in East Tennessee.

[16] While both Asa Gray and Eaton identified A. bradleyi as a hybrid intermediate between A. montanum and A. platyneuron, the English botanist R. Morton Middleton proposed in 1892 that it was identical or closely related to A. viride.

This conclusion was based on the examination of forms growing in shade on the Cumberland Plateau which lacked color in the rachis, and was endorsed by contemporary Tennessee botanists such as Augustin Gattinger and Kirby Smith.

[17][9] This was rebutted in 1893 by Amos A. Heller, who pointed out that most collections of A. bradleyi had a dark stipe and that it possessed an auricle (the acroscopic pinnule) which A. viride lacked.

[9] Edgar T. Wherry speculated at length on the hybrid origins of A. bradleyi and other Appalachian spleenworts in 1925, but the scheme he proposed was later found to be untenable, although he did recognize the contribution of A. platyneuron to its ancestry.

[19][d] His cytological studies the following year showed that A. bradleyi was an allotetraploid, the product of hybridization between A. montanum and A. platyneuron to form a sterile diploid, followed by chromosome doubling that restored fertility.

This showed that it was not descended to A. pinnatifidum, whose chromatograms contain compounds inherited from walking fern (A. rhizophyllum), and verified that A. stotleri was simply a form of A. bradleyi.

[2] The sterile diploid hybrid of A. montanum and A. platyneuron, which resembles A. bradleyi except for its abortive spores and smaller sori, was not collected until 1972, at Crowder's Mountain, Georgia.

[14] Specimens believed to be A. bradleyi × platyneuron were collected at an early date at McCall's Ferry, along the Susquehanna River.

[31] It usually grows tightly wedged into horizontal or vertical crevices in exposed rock or cliff faces.

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.

NatureServe considers it critically imperiled (S1) in Indiana, Illinois, Maryland, New Jersey, Oklahoma, Ohio, Pennsylvania, South Carolina, and West Virginia, imperiled (S2) in Alabama, Georgia, North Carolina, Tennessee, and Virginia, and vulnerable (S3) in Kentucky.