Stems pilose, trichomes appressed, malpighiaceous, or minutely stalked, forked, plants rarely glabrescent. Basal leaves: blade surfaces pubescent, trichomes sessile, forked, and/or stellate. Fruits (4-)4.5-6(-6.5) cm; style 0.5-1.3 mm. Flowering Mar-Jun. Ravines, pastures, cliffs, calcareous talus, dolomite glades, rich woods, bluffs, rocky ledges; 0-300 m; Ont.; Ill., Ind., Iowa, Kans., Mo., N.Y., Ohio, Pa., Tenn., Va. R. C. Rollins (1941, 1993) recognized both pycnocarpa and adpressipilis as distinct varieties of Arabis hirsuta; G. A. Mulligan (1996) treated adpressipilis as a synonym of A. hirsuta var. pycnocarpa. In my opinion, the differences in trichome morphology of the stems and leaves are significant enough to justify recognition of infraspecific taxa of one species.
From Flora of Indiana (1940) by Charles C. Deam
Infrequent to rare in the state and probably absent from some of the central counties. It grows in sandy soil in alluvial bottoms, in crevices of rocks, and on rocky slopes and high banks of streams. Since all of my specimens are from the borders of streams and lakes, its affinity for them is apparent. This species is variable in its pubescence which is sometimes restricted to the lower part of the plant. Its pubescence, strict habit, and its habit of sending up several erect branches from the base usually identify it.