Humans have always relied on plants for medicine and many modern remedies are still derived from plants.
Blessed milk thistle, or Silybum marianum, isn’t so holy when it forms prickly, invasive thickets. Conservationists quick to eradicate it from Maui pastures. Photo courtesy of Maui Invasive Species Committee
The active ingredient in aspirin, salicylic acid, is now synthesized in a lab but used to be obtained from the bark of willows, or plants in the genus Salix. Digitalis, a drug for heart conditions, is one of a group of medicines extracted from the foxglove plant, Digitalis purpurea. An Alzheimer’s treatment, galantamine, is either produced in the lab or extracted from daffodils. Present-day herbalists harvest or grow plants to treat everything from acne to weight loss.
But while they may have health benefits for people, some medicinal plants may sicken our environment. Mullein, notable for its use as a respiratory aid and a remedy for skin problems, is one example. Common mullein, or Verbascum thapsus, thrives on bare soil at mid to high elevations—think the painted landscape of Haleakalā crater. It can monopolize the habitat of native plants, such as the iconic silversword. Mullein is not established on Maui, but the cinder slopes of Mauna Kea and Mauna Loa on Hawai‘i Island are now covered with this highly invasive plant.
Blessed milk thistle, or Silybum marianum, is renowned to herbalists for protecting the liver from poisons. This thorny thistle is equally famous for its invasiveness. Darwin commented on the impacts of this European native as he rode through the pastures of Argentina: “When the thistles are full-grown, the great beds are impenetrable…” He continued to describe the murderous robbers who hid amongst the thistles. Blessed milk thistle has been found in a Makawao pasture, and is on track for removal. At one time this plant was in cultivation on Maui for its medicinal properties. Fortunately that is no longer the case.
Mullein, or Verbascum thapsus, invades on the open slopes of Mauna Loa and Mauna Kea. This medicinal plant is not a good prescription for the environment. Photo by Forest and Kim Starr.
There is much to be learned from studying plants. The practices of herbalism in naturopathy, traditional Chinese medicine, or lā‘au lapa‘au, Hawaiian plant medicine, all stem from living close to nature. Knowing when to harvest plants and what parts to use is an impressive skill. So too is knowing which plants to grow and where.
Hawai‘i is home to a diversity of plants and animals found nowhere else in the world, some with healing properties. When non-native, invasive species become established, they disrupt the interdependent relationships that characterize healthy, intact native ecosystems. Growing medicinal plants can be a way to revive and retain ancient types of knowledge. It can be an avenue to connect with your natural surroundings. And, with a little forethought, it can be done in balance with the environment.
If you are going to grow your own medicinal plants, choose species that are not invasive or otherwise harmful. The common artichoke, for example, has the same liver-supporting compounds as blessed milk thistle, without the invasive characteristics.
How can you determine whether a plant is problematic? The Hawai‘i Pacific Weed Risk Assessment is a screening tool that evaluates plant species’ biological characteristics and their potential for becoming invasive. Check it out at www.plantpono.org.
By Lissa Fox Strohecker. Originally published in the Maui News, May 12th, 2013 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.
