blue toadflax

Blue toadflax is an early season prairie wildflower. It is native to North America, Mexico, and western and southern South America. It is sometimes cultivated as an ornamental. It was introduced and is naturalized in Japan, North and South Korea, eastern Russian Federation, and the Indian subcontinent. In the United States it is common in the south and on the East Coast. It is uncommon in the southeast and metro regions of Minnesota, where it is at the northwestern extent of its range, and it is absent from the remainder of the state. It is found in prairies, old fields, roadsides, and disturbed sites. It grows under full sun in dry, sandy soil.

Blue toadflax is an annual forb that rises on two kinds of stems from a small taproot. First to appear is a radiating cluster (rosette) of a few to several vegetative stems. Vegetative stems are ⅜″ to 2⅜″ long (1 to 6 cm) long, hairless, and usually unbranched. They usually lay flat on the ground (prostrate), sometimes with just their tips ascending (decumbent). Some may eventually reach 4″ (10 cm) in length with age. Later, one to four flowering stems emerge. Flowering stems can be 4¼″ to 27½″ (11 to 70 cm) tall but are usually no more than 20″ (50 cm) in height. They are usually erect, but sometimes curve upward very near the base (strongly ascending), and are usually unbranched, but sometimes have a few branches near the tip. They are hairless below the inflorescence. Both kinds of stems are slender, round, and green to reddish-green. Vegetative stems are often withered or absent at flowering time.

Leaves on vegetative stems are opposite or in whorls of three, 1⁄16″ to ½″ (2 to 12 mm) long, and 1⁄64″ to ⅛″ (0.5 to 3.0 mm) wide. They may be stalkless or on short leaf stalks. The leaf blades are narrow and inversely egg-shaped or elliptic. Leaves on flowering stems are alternate, unstalked, 3⁄16″ to 1⅝″ (5 to 43 mm) long, and 1⁄64″ to 1⁄16″ (0.5 to 2.2 mm) wide. The leaf blades are linear or thread-like. Leaves of both kinds of stems are unlobed, hairless, and untoothed.

The inflorescence is a slender, up to 7″ (18 cm) long, unbranched arrangement (raceme) of flowers at the end of the flowering stem. The flowers are widely spaced on the raceme, even at the start of flowering time. Each flower is on a 1⁄32″ to ¼″ (1 to 7 mm) long, erect or strongly ascending stalk (pedicel). At the base of the pedicel there is a single 1⁄32″ to ¼″ (1 to 7 mm) long, linear, bluntly pointed, modified leaf (bract).

The flowers have both male and female reproductive parts (perfect). They bloom from mid-May to mid-June. Each flower is 5⁄16″ to ½″ (8 to 13 mm) long including the spur. There are 5 outer floral leaves (sepals), 5 petals, 4 stamens, and 1 style. The sepals, together referred to as the calyx, are united at the base then separated into 5 narrow, sharply pointed, 1⁄16″to ⅛″ (2.1 to 3.5 mm) long lobes. They are green to purplish-green and sometimes hairless but more often glandular-hairy toward the base. The petals, together the corolla, are light blue to light purplish-blue. They are united at the base then separated into two unequal lips. The upper lip is 1⁄32″ to 1⁄16″ (1.2 to 2.0 mm) long, sometimes a little longer, and divided into two equal lobes. The lobes are erect or slightly angled backward. The lower lip is 1⁄16″ to ¼″ (2 to 5 mm) long and is divided into three rounded, spreading lobes. The base of the lower lip is white and strongly arched. A nectar spur extends backward from the throat of the corolla. The spur is 1⁄16″ to ¼″ (2 to 7 mm) long and may be straight or curved. The stamens are arranged as two pairs of unequal lengths. The stalks (filaments) are hairless. The style has an unlobed, cap-like stigma.

The fruit is a ⅛″ (2.6 to 3.9 mm) long, ⅛″ (2.6 to 3.3 mm) wide, oblong egg-shaped capsule with 100 to 200 seeds.

4¼″ to 27½″ (11 to 70 cm)

Light blue to light purplish-blue and white

Kalm’s lobelia (Lobelia kalmii) basal leaves are spatula-shaped. It occurs in wet areas.

Dry. Prairies, old fields, roadsides, and disturbed sites. Full sun. Sandy soil.

Mid-May to mid-June

Sources

2, 3, 4, 5, 6, 24, 28, 29, 30.

Native

Uncommon in Minnesota

This species was formerly classified as Linaria canadensis. This and three other Linaria species were transferred to the new genus Nuttallanthus in 1988 based on characteristics of the flowers and the seeds.

Plants were in bloom. I have photos is you would like me to send them. There were about a half dozen plants present. This is an area that is commonly used by people in the summer, so I worry about it getting trampled.

Nuttallanthus canadensis, the blue toadflax. 3 Minutes plants. Simple flower/plants movie. 3分間の植物動画
ethnobotaist isamimasi

Leanne Hinke
5/19/2024

Location: Sandy beach on the Mississippi River. Across from the power plant at Genoa. (Houston County)

Plants were in bloom. I have photos is you would like me to send them. There were about a half dozen plants present. This is an area that is commonly used by people in the summer, so I worry about it getting trampled.

Location: Kellogg Weaver Dunes SNA, Weaver Dunes Unit