Milkweed is a common name for plants in the genus Asclepias. Over 100 species can be found in this genus, living in a variety of environments all over the world. Some are treated as literal weeds and nuisance plants, but they are also grown as ornamentals and companion plants. Some garden stores offer several cultivars.
These plants have simple leaves, umbel-shaped flowers, and a distinctive milky sap. The sap looks almost like latex, and at one point, people tried to refine it into a form of natural latex, unsuccessfully. Milkweed sap is also a mild skin irritant, and it can be toxic if it enters the bloodstream. When the plants go to seed, the umbels burst open to reveal pods filled with tiny, feathered seeds that are borne on the wind across great distances.
Depending on the species, milkweed may be orange, white, yellow, purple, pink, or a variety of other colors, and the height of the plant varies. Most plants produce a nectar that is especially appealing to butterflies, although other insects may be drawn to it as well, and many birds also enjoy the nectar. This leads some people to grow it in their gardens to attract butterflies and birds. The plant is also used by some bee species. Garden stores which specialize in plants for butterfly or bird gardening often carry milkweed, usually in a range of colors for gardeners to choose from.
While milkweed attracts some insects, it also repels some insect pests, which can make it a good companion plant. When planted around the garden, it may prevent crop pests from settling, and it will keep pests out of ornamentals as well. Depending on the cultivar, milkweed can be grown in USDA zones 3 through 9, and there are some exceptions which fall outside this range, and it usually has minimal water requirements. In warmer climates, it is usually a perennial, although some species are annuals.
Milkweed has historically been used in folk remedies to treat warts and rashes, although it can irritate the skin. It has also been used as a source of toxin for poisonous arrows, demonstrating the considerable variation between various species. Some enterprising individuals even used the fine hairs on the seeds to spin rope and thread historically, although there are more efficient sources of plant fiber for such tasks.
This plant was also used in folk medicine in Europe, inspiring the genus name, which is a reference to the Greek god of medicine. The use of toxic plants in medicine in Europe was actually quite common historically, with many doctors believing that the resulting vomiting, fever, and other symptoms of poisoning were indicators that a disease was being expelled from the body.