On moist ground, Water Parsnip initially forms a rosette of basal leaves up to 1½' across. In shallow water, this wildflower initially forms a cluster of aquatic or semi-aquatic leaves of variable length. The terrestrial basal leaves are very similar to the alternate leaves (described below), except the leaflets of the former are wider. Fully aquatic leaves are double-pinnate or double-pinnatifid with filiform leaflets or lobes that are pale green and glabrous. Semi-aquatic leaves are primarily odd-pinnate with linear to linear-lanceolate leaflets; these leaflets usually have narrow pointed lobes along their sides. In addition, semi-aquatic leaves may have whorls of secondary leaflets at the bases of the primary leaflets. These secondary leaflets are similar to the primary leaflets, except the former are smaller in size. Regardless of which kind of leaves has been developed, this is followed by a flowering plant 2½-6' tall (above the ground or water surface) that branches sparingly. The stems of the flowering plant are light green, glabrous, and longitudinally veined; they are terete or angular-terete in cross-section. Alternate leaves along the stems are up to 1½' long and about one-half as much across; they are odd-pinnate with 7-17 leaflets. The leaflets of these compound leaves are 1½-4½' long and ¼-1¼' across; they are linear-lanceolate to narrowly lanceolate in shape and their margins are finely serrated. The upper surface of these leaflets is medium green and glabrous, while the lower surface is pale green and glabrous. The lateral leaflets are sessile, while the terminal leaflet of each compound leaf has a short petiolule (basal stalklet) up to 1' long. Each compound leaf has a sheath that extends along the entire length of its petiole (¼-4' long); the lower leaves have longer petioles than upper leaves. Both the petiole and rachis of each compound leaf is medium green, glabrous, and angular; they are often finely grooved along their upper surfaces.