It can be either annual or biennial. Leaves are greyish and softly haired, lanceolate to oblong. Reddish-purple funnel-shaped flowers bloom between May and September.

The plant owes its common and scientific name to the long greyish leaves that are reminiscent of a dog's tongue and were once given as a remedy for dog bites.^[3]

Found in most parts of Europe, and also North America, where it was accidentally introduced^[4] including in British Columbia, where it is designated a noxious weed under the British Columbia Weed Control Act.^[5] It lives in wet places, sand dunes, waste land and hedges.

Houndstongue may be pollinated by bees, and may also self-pollinate.

The name "houndstongue" (and the Latin genus Cynoglossum) comes from the roughness of the leaf.

In 1725, houndstooth was presented in the family dictionary, Dictionaire oeconomique, as part of a cure for madness.^[6] In that book, madness was viewed as "a distemper, not only of the understanding, but also of the reason and memory, proceeding from a cold, which drys up everything it meets with that is humid in the brain."^[6] To cure madness, Dictionaire oeconomique noted:

You must shave the head of the unhappy patient, and after that, apply to it a pidgeon, or a hen quite alive; or else bathe it with some brandy distilled with rosemary, elder, hounds tooth, and the roots of bugloss, or with the oyl of elder flowers: they rub their heads and wash their feet with a decoction of the flowers of camomile, melilot, balm gentle and laurel; they put into their noses the juice of comfrey, with either two or three spoonfuls of honey-water, broth, or white-wine, wherein wormwood and sage are infus'd ; or else they do for five and twenty days together, mix with their broth in the morning, halt a dram of the ashes of tortoise, and they put into the pot bugloss, borage, with a pinch of rosemary to season it.^[6]

In the 1830s, houndstooth was known in France to be made into an emollient and diuretic for daily use in inflammatory diseases, especially of the urinary organs.^[7] To prepare as a diuretic, the houndstooth leaves were mashed, and then boiled in water to extract oils, volatile organic compounds, and other chemical substances.^[7] The mix could be sweetened with liquorice to create Ptisan of Dog's-grass.^[7] After decoction, the herbal tea was taken internally a cupful at a time.^[7] In 1834, the Hospital of Paris provided a formula of 2/3 ss—J to Oij of water for houndstooth tea.^[7] By the end of the 1830s, doctors in England were using houndstooth as an antiaphrodisiac to combat venereal excesses.^[8]

Herbalists use the plant for piles, lung diseases, persistent coughs, baldness, sores, and ulcers but the effectiveness of all these uses is not supported by any scientific evidence.^[9]

In 1891, the U.S. state of Michigan identified houndstooth, along with flea-bane, rag weed, burdock, cockle-bur, and stickseed, as some of the worst weeds in the state.^[10]

Cynoglossum officinale contains tumorigenic pyrrolizidine alkaloids.^[11] It is toxic to cows and is especially dangerous to pasture owners.^[4]

• Blanchan, Neltje (2002). Wild Flowers: An Aid to Knowledge of our Wild Flowers and their Insect Visitors. Project Gutenberg Literary Archive Foundation.

• Species Profile - Houndstongue (Cynoglossum officinale), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Houndstongue.