Great blue lobelia

Conservation Status

IUCN Red List

not listed

NatureServe

NNR - Unranked
SNR - Unranked

Minnesota

not listed

Wetland Indicator Status

Great Plains

OBL - Obligate wetland

Midwest

OBL - Obligate wetland

Northcentral & Northeast

FACW - Facultative wetland

Description

Great blue lobelia (var. siphilitica) is a 12″ to 48″ tall, erect or strongly ascending, perennial forb that rises from a taproot.

The stems are erect, stout, leafy, and angular, at least near the top. They are usually unbranched, sometimes there are a few branches toward the top. They are mostly hairless but may be sparsely covered with short hairs on the angles.

The leaves are alternate, thin, lance-shaped to elliptic or inversely lance-shaped, ¾″ to 6″ long, and ¾″ to 2⅜″ wide. They taper to a point at the tip and are tapered or angled at the base. They are stalkless or on short leaf stalks. The upper and lower surfaces are hairy. The margins are finely, irregularly toothed.

The inflorescence is a spike-like, unbranched, elongated, 4″ to 12″ long cluster of usually 20 to 60 flowers at the end of the stem. The flowers are on ascending, hairy, ⅛″ to 5 ⁄16″ long stalks. The stalks have a pair of bracts at or above the middle and a pair of minute bracteoles at the base of or just below the calyx. The bracts are leaf-like in the lower part of the inflorescence, gradually becoming smaller as they ascend the stem.

The flowers are ⅝″ to 1¼″ long and about ½″ wide. At the base there are 5 are lance-shaped, hairy, 5 ⁄16″ to 11 ⁄16″ long sepals that are fused at their base into a bell-shaped, 1 ⁄16″ to ⅛″ long tube, then separated into 5 slender, ¼″ to 9 ⁄16″ long lobes. At the base of each lobe of the calyx is a pair of long, conspicuous projections (auricles).

There are 5 blue to bluish-purple petals fused at their base into a 7 ⁄16″ to ¾″ long corolla tube, then separated into an upper and lower lip with spreading, 3 ⁄16″ to ½″ long lobes. The tube has slit-like openings and is sometimes striped with white. The lower lip is large with 3 lobes, the upper lip is smaller and split nearly to the base into 2 spreading lobes. There are 5 stamens. The filaments are fused from just above the base into a ½″ to ⅝″ long tube surrounding the style. The anthers are fused into a ⅛″ to 3 ⁄16″ long ring around the style. The style and filament tube protrudes from between the 2 lobes of the upper lip and bends downward near the tip. The flowers are not fragrant.

The fruit is a yellowish-brown, 3 ⁄16″ to ⅜″ long capsule, ellipse-shaped lengthwise, round in cross section.

Height

12″ to 48″

Flower Color

Blue to bluish-purple

Similar Species

Great blue lobelia (Lobelia siphilitica var. ludoviciana), the western variety of this species, has hairless leaves that are mostly less than ¾″ wide. The inflorescence has 6 to 20 flowers. The flower stalks and calyces are hairless. Minnesota lies where the ranges of these two varieties meet. The plant characteristics that identify each variety intergrade in this area and the varieties may not always be distinguishable (or even valid).

Lobelia siphilitica var. siphilitica f. albiflora is a rare form with all white flowers.

Habitat

Wet to moist. Meadows, streambanks, river banks, bottomland forests, edges of lakes and ponds, swamps, fens, roadsides. Full sun.

Ecology

Flowering

August to September

Pests and Diseases

Use

Distribution

Sources

7, 24, 28, 30.

Biodiversity occurrence data published by: Minnesota Biodiversity Atlas (accessed through the Minnesota Biodiversity Atlas Portal, bellatlas.umn.edu. Accessed 9/16/2026).

Midwest Herbaria Portal. 2026. https://midwestherbaria.org/portal/index.php. Accessed 9/16/2026.