The Russian comfrey (Symphytum × uplandicum Nyman) is a cultivated perennial herb reaching about 1 m high with large, lance-shaped hairy leaves, hairy stems and magenta-pink flowers (Bareeba et al., 1992; Göhl, 1982; Boonman, 1993; Teynor et al., 1997). The root system of a well-established comfrey plant is fleshy and extensive. The plant can be harvested for both leaves and tubers (Bareeba et al., 1992; Boonman, 1993).
Comfreys have been used as traditional medicinal plants in Europe for centuries, and have been presented in the 19th century as "wonder plants" for food and forage. Russian comfrey has been a staple of organic gardening and commercial herbal medicine since the 1950s due to its allantoin content, which is used by herbalists for treating digestive disorders (Teynor et al., 1997; Bareeba et al., 1992). However, in the 1980s, the use of comfrey leaves was recognized as a substantial health hazard causing hepatic toxicity in humans and with carcinogenic potential in rodents due to the presence of toxic pyrrolizidine alkaloids (see Potential constraints on the "Nutritional aspects" tab). This led to the ban of certain comfrey-based herbal products in several countries (Culvenor et al., 1980; Stickel et al., 2000).
As a fodder, Russian comfrey is valuable for its quick regeneration from the large food reserves in the roots, an ability that once earned the plant the nickname of "world's fastest protein builder" (Bareeba et al., 1992). It used to be promoted as a high-yielding protein-rich forage crop, a promise that was not supported by research data. Because of low yields and digestibility values, high cost of establishment and weed control, and low palatability to some animal species, some authors were not able to recommend Russian comfrey as a forage crop (Hart et al., 1981).