Wildflowers of the United States

Blue Toadflax, Canada Toadflax, Oldfield Toadflax - Nuttallanthus canadensis

Family: Plantaginaceae - Plantain family

Native Status: Native

Dicot Annual Biennial Herb Leaves:Opposite Leaves:Alternate Leaves:Whorled

Nuttallanthus canadensis - Blue Toadflax, Canada Toadflax, Oldfield Toadflax.
The three native North American and single native South American species of Linaria were separated into the four-species genus Nuttallanthus in 1988 by David A. Sutton in his comprehensive treatment of the tribe Antirrhineae which is now placed in the Plantaginaceae (formerly within Scrophulariaceae.) The remaining species of Linaria are Eurasian in origin. Some use American Toadflax as the genus common name for Nuttallanthus.

Of the three species found in the United States, Nuttallanthus floridanus is, as the name implies, primarily a Florida species, but also found in the adjoining Southeastern states of Georgia, Alabama, and Mississippi. N. texanus is a more western species, found sporadically in the Southeastern states, but mostly centered west of the Mississippi in the south central U.S, and scattered through most of the rest of the West, and into Canada. N. canadensis, the one presented here, is an eastern species, found in all states east of the Mississippi River and west to Texas and north to Minnesota and Canada. (There is some disagreement as to whether this plant is found in North and South Dakota.) While several reliable organizations report it as being in California, Oregon, and Washington, it is possible that is not present there. Some of the confusion on those western states might be because Nuttallanthus texanus was once classified as Linaria canadensis var. texana. I know that at least one source has (as of 2019-01-12) photos of what appears to me to be Nuttallanthus texanus but listed as Nuttallanthus canadensis.
Synonym: Linaria canadensis

Found in:
AL, AR, CT, DC, DE, FL, GA, IA, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MS, NC, ND, NH, NJ, NY, OH, OK, PA, RI, SC, SD, TN, TX, VA, VT, WI, WV, GS

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Distribution of Nuttallanthus canadensis in the United States and Canada:

Map courtesy of The Biota of North America Program.
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Site: Lula Lake, Walker County, Ga Date: 2018-April-28	Photographer: Gerald C Williamson
The blue to lavender flower of Blue Toadflax is two-lipped, with the lower lip being much larger than the upper lip - a differentiator with the Linaria species. That lower lip is three-lobed has two white ridges. The upper lip is two-lobed. The corolla has a thin spur; Linaria species' spur is stouter.

Site: Lula Lake, Walker County, Ga Date: 2018-April-28	Photographer: Gerald C. Williamson Nikon D7000 Tamron SP 90MM f/2.8 AF Macro
My initial identification as Nuttallanthus canadensis was based largely on the location - N. texanus isn't known in Georgia on Lookout Mountain near its northern terminus (although it is known in Alabama near the southern terminus of the mountain.) However, N. canadensis also has a smaller flower, usually less than 1/2 inch, while that of N. texanus is usually more than 1/2 inch long, up to almost 1 inch.
Click on the photo for a larger image
Site: Lula Lake, Walker County, Ga Date: 2018-April-28	Photographer: Gerald C Williamson Nikon D7000
Blue Toadflax grows to about 2 feet tall. The flowering stems are almost leafless, with a few alternate leaves on the lower stem. The stems are green to reddish.
Click on the photo for a larger image
Site: Lula Lake, Walker County, Ga Date: 2018-April-28	Photographer: Gerald C Williamson Nikon D7000
Shown poorly here, there is a rosette of mostly-prone leafy (non-flowering) stems. They usually have opposite leaves, which are linear and up to an inch long.
Click on the photo for a larger image

References used for identification and information:

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Nuttallanthus canadensis initially published on USWildflowers.com 2019-01-12; Updated 2019-01-12

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All content except USDA Plants Database map Copyright Gerald C. Williamson 2024
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Code Update 20230302