Plant of the Week
Heartleaf Arnica (Arnica cordifolia)
By Walter Fertig
Many plant-lovers get discouraged with identifying the myriad species of yellow-flowered composites in the aster or sunflower family (Asteraceae). Telling genera and species apart among the “DYC”s (damn yellow composites) can require mastery of arcane botanical terminology and observation of minute floral and fruiting parts not always readily apparent to the naked eye. Thankfully, the arnicas (genus Arnica) are relatively simple to identify. They are the only genus of yellow-rayed composites that regularly have opposite, simple leaves (not divided into leaflets) and hair-like (capillary) bristles topping the fruits. All of these features can be seen without magnification.
Just because the genus is easy to recognize, however, doesn’t mean that individual species are so distinctive. Taxonomists recognize 29-32 species of Arnica across the Northern Hemisphere, with 26 native to North America. Some of these species apparently arose through hybridization, while others maintain themselves by apomixis (production of viable seed by asexual means, rather than cross-pollination). Polyploidy is also present in many species, with the same population often containing diploids, triploids, and tetraploids. The result of all of this genetic re-shuffling and clonal reproduction is the creation of a lot of morphological variability that can blur species boundaries.
Fortunately, Heartleaf arnica (Arnica cordifolia) is one of our more easily identifiable Arnica species. The plant derives its common and scientific names from its basal leaves which usually have a deep, heart-shaped notch at the base. The lower leaves are borne on long petioles (leaf stalks) and have coarsely-toothed margins. By comparison, other Arnica species generally have sessile or smooth-margined leaves or at least lack the heart-like shape. Arnica cordifolia can also be recognized by its single (occasionally 2-3) large and showy flower head of bright yellow petal-like ray flowers surrounding a central cluster of small, yellow tubular disk flowers. Heartleaf arnica is one of the most widespread of the arnicas in North America, occupying forests, thickets, and streamsides in the mountains from Alaska and western Canada to central California, Arizona, and New Mexico (with isolated populations in Michigan).
Europeans and Native Americans independently discovered the medicinal qualities of Arnica species. For centuries, the European species Arnica montana has been used to treat acne, bleeding, and pain. More than 100 arnica-based teas and preparations are still marketed in Germany, though physicians caution against over-consumption or taking it internally, as the plant can be toxic. Native Americans used the root of Heartleaf and other arnica species to treat sort throats, aching teeth, cuts, and bruises. Mixed with ocher and bird feathers, arnica was also used as a sort of love potion. No word from the medical community on the efficacy of the latter.