Ledum is a genus that was formerly classified under the family Ericaceae. As of 2010, it is recognized under the family Rhododendron because of new genetic evidence. This genus is composed of eight species of evergreen shrubs. It is native to cooler climates in the subarctic regions of the northern hemisphere, especially Canada, the United States, and Scandinavia. The leaves and shoots of these plants are used as spice, medicine, and insect repellent.
These shrubs grow to a height of 3 feet (1 m). Their flowers usually bloom from April to June, but they have leaves all year through. They are hermaphrodites, with both male and female organs, and they are pollinated by bees. The flowers contain oil that smells like antispectic, and the highly aromatic leaves smell strongly of hops when crushed. Ledum thrives in any shade, but the plants flower more profusely when fully exposed to the sun. These types of plants require moist humus-rich soil that is sandy, peaty, or loamy acidic.
The species Ledum groenlandicum, or Rhododendron groenladicum, is commonly known as labrador tea. It has white flowers and characteristic leaves with edges that are curled under and thick, hairy tan undersides. The tea, brewed from its leaves, is used in folk medicine to treat external skin irritations and is drunk to settle the nerves and stomach. It can also be made into syrup to treat cough and throat hoarseness.
Leaves of the Ledum palustre, renamed Rhododendron palustre, and more commonly known as wild rosemary, can be made into an aromatic tea. This is used in homeopathic therapy in powdered form for ailments such as kidney ailments, joint pains, and menstrual pain. Its aromatic tea is consumed for asthma, cough, and stomach aches. Homeopaths believe Palustre has the ability to heal tissue from its deepest point, going outward to the surface, and is therefore used for insect bites, lacerations, and puncture wounds. It is given also to people who have rheumatic pains or painful joints.
Palustre is also used in the kitchen as a substitute for bayleaf. It was once used as a substitute for hops in beer making, but it caused a different kind of drunkenness accompanied by headache and dizziness. In Scandinavia, the leaves were once placed in closets to repel insects while the branches were placed with grains to repel mice. When growing or handling this plant, one must be careful, as all parts of it contain a poison that attacks the central nervous system; the mere smell can cause headache.