The leaves of lomatium plants are often the best means of identifying similar-looking species; those of lomatium dissectum
are ternate, divided three times, first into well separated, opposite pairs, then into more closely-spaced alternate leaflets, and finally to two or three smaller, pointed lobes; usually narrow and non-overlapping. Leaves grow on stalks, up to 12 inches long, similar to the length of the blade. This is one of the largest lomatium species, reaching heights of 4 feet or more. Leaves and stems are usually smooth and hairless, but can have a covering of short, fine hairs. Leaves grow mostly from the base, spreading upwards and outwards.
Plants produce many stems, topped by flat-topped clusters of tiny flowers, which may be yellow or orange-red in color. The inflorescence is a compound umbel of 10 to 30 umbellets, each bearing a dozen or so flowers. There are two varieties, var dissectum and var multifidum, differentiated by pedicel length and fruit attachment (sessile or pedicelled).