Lobelia siphilitica L.

Blue Cardinal Flower

Lobelia siphilitica plant

Family - Campanulaceae

Stems - To 1m tall, angular, glabrous to pubescent on angles, herbaceous, with milky sap.

Lobelia siphilitica stemStem with milky sap.

Leaves - Alternate, sessile, oblong to lanceolate or oblanceolate, 2-6cm broad, to 15cm long, crisped or toothed(or both) on margins, typically pubescent on both surfaces, acute at the apex.

Lobelia siphilitica leaves

Inflorescence - Terminal raceme with +20 flowers. Flowers subtended by foliaceous bracts.

Lobelia siphilitica inflorescenceInflorescence

Flowers - Resupinate. Corolla purple-blue, tubular, 2-3cm long, with perforations (fenestrate), 5-lobed. Filaments united into a tube to 1.5cm long and surrounding style. Pedicels with pair of small bracteoles at or above the middle. Calyx pubescent to glabrous, +/-1.5cm long. Calyx lobes 5-6mm broad, with auricles at base.

Lobelia siphilitica calyxCalyces.

Lobelia siphilitica flowerFlower.

Lobelia siphilitica flower

Flowering - August - October.

Habitat - Wet areas.

Origin - Native to U.S.

Other info. - Steyermark splits the species into two varieties, the most common being variety siphilitica. A white flowered form of var. siphilitica, fo. albiflora, is presented on the "White flowers alternate" portion of this website. Another form, fo. purpurea Palmer &Steyermark, has very deep purple flowers. The second variety is variety ludoviciana A. DC., which has fewer flowers in the inflorescence and leaves and stems which are mostly glabrous. Because the two varieties intergrade and most Missouri material lies somewhere in between, Yatskievych chose not to formally recognize these varieties.

This species is quite common along pond margins and and in wet woods and meadows. The brilliant flowers have earned the plant a place in cultivation and it is becoming quite common. The plant contains piperidine and tetrahydropyridine alkaloids and is somewhat toxic.

Like many members of our flora, this one can occasionally be found with flowers lacking pigmentation. This white form has been called f. albiflora Britton. A photo is shown below.

Lobelia siphilitica albifloraf. albiflora.

Photographs taken at the Kansas City Zoo, 8-13-99 (f. albiflora) and in the Ozark Scenic Riverways, Shannon County, MO., 8-15-03(DETenaglia); also at Little Lost Creek Conservation Area, Warren County, MO, 9-6-2015 (SRTurner).