PlantFiles: Common Toadflax, Bread and Butter, Brideweed, Bridewort, Butter and Eggs
Linaria vulgaris

MN DNR's website has this plant listed on the invasive list.
"Ecological Threat:
This plant has the ability to adapt to various site conditions, in Minnesota it grows on gravelly to sandy soil along roadsides, railroad yards, waste places, dry fields, pastures and croplands.
It competes well against less aggressive native plants in gravelly and sandy soils; its capability to spread also vegetatively is largely responsible for its invasive behavior.
It presents a problem in prairie reconstruction projects, once it has established itself.
This plant is a serious problem in Alberta and is on the state noxious weed list in New Mexico and Arizona.
This plant was introduced into North America as an ornamental from the steppes of Europe and Asia in the 1700s, and is still sold commercially. "

It grows everywhere here, so if you want some and it is not considered invasive where you are-let me know and I will go pull it from the cracks along the roads :o)

This plant is listed on the North Dakota invasive/troublesome list and this information is being distributed in a guide developed by the ND Weed Control Association and other agencies.

Plant Features
Perennial, up to 2 feet tall
Numerous soft leaves are long, narrow, pale green and are attached directly to the stem
Bright yellow snapdragon-like flowers with a bright orange throat and long yellow spur
Blooms May through September
Spreads by creeping roots (rhizomotous, spreads laterally 10 feet per year), and seeds

Distribution
Widespread invasive that grows under most conditions
Very aggressive, tolerates shade
Very difficult to eradicate

Interesting Facts
Gardeners call it butter-and-eggs
Flowers resemble Dalmatian toadflax
A single plant can produce up to a half-million seeds per year
May be mildly poisonous to livestock (contains glucoside) if ingested
Escaped ornamental, known to be planted in cemeteries

Toadflax is Very Dangerous to Livestock,if you have live stock and it can get into your pastures,it can kill your stock...I wanted to grow this but now I'm scared to because we have horses and it spreads to easy and is a weed to ranchers and livestock owners..:-(

Very Cheery and delightful plant

It is considered a noxious weed here in Saskatchewan, the local R.M. spray it where ever it is spotted. Has been spread quite extensively by the snow-machines.
Beautiful flowers, such a cheery yellow but we find it so hard to get rid of or even control.

A perennial from Europe.

Has grey-green, linear or lance shaped, almost hairless leaves. Bears 2 lipped, pale yellow flowers with a dark gold spot on the lower lip, behind the flower is a conspicuous spur.

Flowers June-October

Loves moist but well-drained, soil in full sun but can tolerate a wide range of soils and situations. It can become invasive via it's creeping root system and self-sows quite easily.

The common name Toadflax derives from the time when Flax (Linum usitatissimum) was widely grown as a fibre crop. This Linaria would happily self sow within the Flax and grow virtually unnoticed until it flowered. It has no use at all for fibre making and could devalue the crop.

It was once considered a cure for jaundice under the Doctrine of Signatures but was also used as a diuretic. It's still sometimes used as a diuretic today by trained herbalists.

Other British country names for Toadflax are:
Weasel Snout
Lion's Mouth
Pig's Chops
Dragon Bushes
Fox and Hounds

Well-drained, moist soil. Propogate by seed, self sows