The genus Symphytum, commonly called Comfrey, is a widespread genus native to Europe, but is particularly common around the Mediterranean region. They commonly have hairy leaves, some as long as two feet, with either soft or rough hairs covering the plants. The flowers are borne on scorpioid cymes and range in color depending on the species from light yellow to dark purple. The flowers are very attractive to bees of various types.
Comfrey in general has a long history of medicinal use due to the high concentrations of Allantoin, used to treat a wide variety of ailments including broken bones and sprains (one common name is 'knit-bone'). Internal use is not recommended because of the varying concentrations of alkaloids reputed to cause liver damage, and in the views of some scientists, cancer. Some strains are reputed to have lower concentrations and different types of alkaloids, apparently allowing limited internal use as a tea or tincture using the roots or eldest leaves, but not while the plant is in flower due to higher alkaloid content then. The safest bet, however, is to avoid internal use and stick to external use by way of poultices made from the roots and eldest leaves chopped, mashed, and wrapped directly over the affected area and left for hours to "do its thing".
The root structures vary from species to species, some being tuberous, rhizomatous, or taprooted while some seem to be a mix of these in functionality. The plants are generally easy to grow. Seed germinates readily after cold stratification or being sown shallowly in the Autumn and left out in the elements until germination in spring. Plants grow easily from root cuttings, which can also make them difficult to remove once planted, often requiring sifting through the soil for root fragments by hand. While not all species are invasive, caution should be taken to ensure the plants do not escape, not as much because they will run rampant through your yard, but so they don't overwhelm neighboring plants, because they will grow quite large. In practice, grow them like you would grow mint, with rich soil, plenty of water, and either physical barriers (below ground) or physical distance from smaller plants.
Like others in the Boraginaceae, they tend to flop over once they reach a large size, and are best chopped to the ground for another round of flowering. This can also help with overzealous self seeding, which may be an issue in some gardens. The seedlings, however, are easy to see and remove or transplant.
See a variety of botanical illustrations here.
Symphytum asperum Lepech is an invasive species that is often found on noxious weed lists, and should never be planted in a garden outside its native range. Rough or Prickly Comfrey is from the Caucasus and appears similar in appearance to common Comfrey (Symphytum officinale).
Symphytum bulbosum aka Bulbous Comfrey. The petals are pale yellow, about 1 inch long. The plant grows from small tubers or rhizomes in wet swampy places.
Symphytum officinale L. is the common Comfrey most often grown in gardens and used in herbal medicine, along with Russian Comfrey (Symphytum x uplandicum), a sterile hybrid of S. asperum and S. officinale. This species, as well as Symphytum x uplandicum are only rarely considered invasive by some gardeners. It is native to the Balkans and other parts of Europe, introduced elsewhere. The roots act as both taproots and rhizomes, growing both very deeply and laterally, but only producing new plants when the thick roots are mechanically broken by digging or some other disturbance. The leaves can grow quite large, up to three feet long, lanceolate to ovate with an accuminate tip. The flowers are borne on inflorescences on branched stalks in conspicuous scorpioid cymes. The flowers are often bicolored with blue, purple, or pink, and possibly shades closer to yellow and white on occasion. Honeybees, bumblebees and other types of solitary bees love the flowers and will search them out eagerly.
This is a large plant that demands a lot of growing space. It can reach up to four feet in all directions. It is best grown in full sun in most climates, part shade where summers are hot (90 °F or hotter). In either situation the plant likes rich water retentive soil that doesn't dry out. It may survive in low areas with stagnant water but will be most fit where good drainage is available. Photos by Travis Owen
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Symphytum tuberosum is a spreading species with yellow flowers. It grows from large rhizomes, and often spreads to form large patches in gardens and the wild. It is native to parts of the UK and surrounding region. The roots are sometimes ground and roasted to make a non-caffeinated coffee substitute like Taraxacum or Cichorium intybus roots.