Yellow toadflax is a member of the snapdragon family and thus easily recognizable by the bright yellow flowers, which have swollen corolla tubes that flare into two “lips” with an orange throat and long spur. The flowers are 1 to 1.5 inches long with many flowers on a raceme. The plants have an extensive creeping rhizomatous root system that spreads like leafy spurge. Yellow toadflax has narrow, linear leaves with a narrow stem.
The plants begin regrowth from the roots as soon as the soil warms in early spring. Toadflax flowers from late June through August in North Dakota and single plants may produce more than 500,000 seeds that are dispersed by wind, rain, wildlife, and movement of forage and livestock. The seed is disk-shaped, 0.08 inch in diameter and dark brown to black, and often have irregular papery wings. Seed dispersal begins a few weeks after flowering and continues into winter. The roots of a single plant can extend 10 feet and give rise to daughter plants every few inches.
Mecinus janthinus is currently being evaluated for yellow toadflax control.
From Lym and Travnicek, 2015, NDSU Circ. W-1411.