Lobelia cardinalis is a perennial herb from basal offshoots (winter rosette), 50 to 150 (rarely) cm tall erect, stout, unbranched, fibrous rooted, usually hairy (Levine 1995), sap milky (Yatskievych 2006).
Leaves alternate, the lower stalks to 3 cm long, upper leaves becoming sessile, blade thin, narrow, 5-20 cm long, 2-5.5 cm wide, elliptic to lance-shaped (Radford et al. 1968), pointed at both ends, margin irregularly toothed.
Flowers scarlet, showy, 3-4.5 cm long, tubular, bilaterally symmetrical, tube 1.7-2.2 cm long, deeply two lipped, the longest 1.5-2.5 cm long, lower lip 3-lobed, upper lip 2-lobed, sepals linear, ca 1 cm long, stamens fused in a red tube 2-3.5 cm long, lower anthers hairy, blue-gray, ovary inferior, 2-parted, style grows through the anther tube and pushes out pollen, stigma 2-lobed, hairy; inflorescence of racemes 10-40 cm long at top of plant, bracts below each flower linear, flower stalks to 1.5 cm long; blooms July-Sept.; pollinated by hummingbirds (Lovell 1918).
Fruit becoming dry, a rounded capsule opening near the top to release numerous yellowish, oblong seeds, each 0.1 cm long, wrinkled (Levine 1995); seeds probably water dispersed.
Wetland status: FACW+.
Frequency in NYC: Infrequent.
Habitat: Swamp forests and marshes, wet edges, soil pH 5.8-7.8, tolerant of shade, intolerant of salt (USDA, NRCS 2006).
Notes: Also planted in wetland restorations. Plant contains toxic pyridine alkaloids typical of other Lobelia spp. and chemically similar to nicotine (Kingsbury 1964). Winter plant with old 2-parted fruit capsules cupped by calyx and parts of corolla (Levine 1995).