Sium carsonii Durand ex A. Gray

Sium carsonii Durand; A. Gray, Man. ed. 5. 196. 1867
Sium cicutaefolium var. Carsonii G. T. Stevens, 111. Guide 442. 1910. Drepanophyllum Carsoni K.-Pol. Bull. Soc. Nat. Mosc. II. 28: 1S3. 1915. Sium suave f. fasciculatum Fassett. Rhodora 23: 111. 1921. Sium suave f. Carsonii Fassett, Rhodora 23: 113. 1921.
Plants weak and slender, often submersed, 2-6 dm. high, leaves oblong to ovate in general outline, excluding the petioles 5-12 cm. long, 3-10 cm. broad, pinnate, the leaflets lanceolate to ovate, 1-6 cm. long, 5-15 mm. broad, distinct and remote, coarsely serrate, or dissected in the submerged leaves, often reduced to the terminal lanceolate to orbicular leaflet; petioles 5-25 cm. long; cauline leaves frequently reduced to the broad terminal leaflet, and bearing similar fascicled leaves in their axils from a corm; peduncles slender, 3-8 cm. long; involucre of 3-5 linear-lanceolate bracts, acute, unequal, 1-10 mm. long; involucel of acute linear bractlets, 1-3 mm. long; rays 5-11, slender, unequal, 1-2.5 cm. long; calyx-teeth minute; halves of the carpophore adnate to the mericarps; fruit oval to orbicular, 1.5-2 mm. long, 1.5-2 mm. broad.
Type locality: "Pennsylvania, around the Pocono Mountain," Green. Distribution: Maine to Pennsylvania; Minnesota. {Fasselt 131, Fernald &■ Long 14,241.)