YELLOW TOADFLAX, butter-and-eggs, wild snapdragon (Linaria vulgaris Mill.). Noxious. Figwort family. This introduced creeping perennial is an escaped ornamental that reproduces by seed and extensive horizontal roots. Stems are smooth, erect, leafy, often in clumps, and 1 to 2 1/2 feet tall. Numerous pale green leaves are alternate, narrow, pointed at both ends, and 2 1/2 or more inches long. Flowers resemble those of cultivated snapdragon; each has a spur extending below from the lower lip of the corolla. They are about 1 inch long, bright yellow with a bearded, orange throat and occur in terminal, somewhat elongated clusters with the youngest flowers at the tip. The fruit is a brown, globe-shaped, two-celled capsule, 1/4 inch in diameter containing many seeds. Seeds are small, round, rough, flattened, with a papery, notched circular wing, dark brown, and about 1/12 inch in diameter. It is a persistent, aggressive invader in Colorado from 6,000 to 8,500 feet mostly on the Western Slope.

Germination and Emergence: Seeds of yellow toadflax germinate and emerge in early to mid-May while Dalmatian toadflax seeds may germinate and emerge earlier especially on south or southeast facing slopes. In Washington, Dalmatian toadflax seedlings on south facing slopes usually emerge in early to mid-March. First year Dalmatian toadflax plants often produce prostrate shoots in fall that survive into the following spring. Mature Dalmatian toadflax may produce prostrate shoots, but to a lesser extent, and these typically die before winter and shoots emerge the following spring from roots. Yellow and Dalmatian toadflax shoots that grow from roots emerge as early as mid-March along the Front Range in Colorado, but vegetative shoot emergence may not begin until mid- to late June at 9,000 feet to 10,000 feet. In Canada, vegetative shoots begin to emerge when soil temperatures range from 42 to 50 F.

Root growth: Seedling root develop is slow and represents a life stage vulnerable to control attempts and plant competition. Disturbance promotes toadflax invasion and may be necessary for establishment to occur. However once established, toadflaxes readily spread into adjacent non-disturbed areas. Much of this spread is by vegetative means, reflecting a vigorously-growing root system. Dalmatian toadflax roots may grow 20 inches deep or more nine weeks after seedlings have emergedand have vegetative buds that give rise to new shoots. Patch expansion can be dramatic. In Colorado, Dalmatian toadflax shoot density increased over 1,200 percent in six years at one location and 190 percent over three years at another. Yellow toadflax seedlings produce vegetative shoots from root buds two to three weeks after germination. Mature toadflax have well-developed and extensive root systems. Dalmatian toadflax roots may penetrate the soil 4 feet to 10 feet and lateral roots may extend 10 feet from the parent plant; while yellow toadflax roots grow 3 feet deep or more with lateral roots that may extend several yards.

Flowering: Dalmatian toadflax typically flowers begining in late May or June in Colorado and may continue until fall, particularly if moisture is not limiting. Yellow toadflax begins to flower when shoots are from 16 to 24 inches tall, mid- to late May along the Front Range in Colorado, although at higher elevations (9,000 feet or more), flowering may not begin until late July. Yellow toadflax may not flower until fall under drought conditions. Yellow toadflax shoot phenology in any given patch may range from vegetative to flowering to seed set, depending on the time of season and environmental conditions (particularly moisture). This contributes to management difficulties.

Origin: The toadflaxes have a storied past and a long relationship with humans. Dalmatian toadflax is native to the Mediterranean region. Broad-leaved Dalmatian toadflax (L. dalmatica) has been cultivated as an ornamental for at least 400 years. It was introduced into the western U.S. as an ornamental in 1874. The majority of Dalmatian toadflax infestations in the west are broad-leaved Dalmatian toadflax; however in its native Eurasian habitat, narrow-leaved Dalmatian toadflax (L. genistifolia) is more widespread, indicating its potential to also invade and become widely dispersed in the U.S. Narrow-leaved Dalmatian toadflax currently infests several areas in western Oregon, northwestern Washington, British Columbia, and possibly in Colorado.
Yellow toadflax is native to south-central Eurasia where it was used for fabric dyes and for medicinal purposes. It was imported into North America in the late 1600s as an ornamental and for folk remedies. It was widely distributed in North America by the mid 20th century. Unfortunately in states where yellow toadflax is not noxious, it still is sold by some nurseries as “butter and eggs” or as “wild snapdragons.”