Name honors Joseph F. C. Rock (1884-1962), Austrian-born American botanical explorer, botanist, geographer, and ethnologist, who lived in Hawai 'i from 1907 to 1920. Among his many publications are the books The Indigenous Trees of the Hawaiian Islands and The Ornamental Trees of Hawaii. While an explorer for the U.S. Department of Agriculture, the National Geographic Society, the Arnold Arboretum, and other organizations, he traveled and worked extensively in southern China.

Blades ovate to ovate-lanceolate, pinnotisect to sometimes fully 2-pinnate, nearly pectinate; basal portions often resemble those of the typical variety. Ultimate segments narrow-linear, 2-3 mm wide, up to 30 mm long, margins entire, slightly crenulate to unevenly sinuate. Sori 1-7 on a lobe.

Rare on Kaua'i, the Ko'olau Range of O'ahu, Moloka'i, and Maui. Intermediates between this and the typical variety have been reported. A few plants have been collected at around 900 m elevation, but its full distribution is not known.

Adenophorus pinnatifidus var. rockii is distinguished from var. pinnatifidus by its longer, narrower, more linear acute-tipped segments arising at an oblique angle from the midrib, and by the presence of more sori on the lobes.