This is the time of year when Blue Cohosh (Caulophyllum thalictroides) comes into its own, brightening the forest floor with its fruit-like seeds which bear fleshy, blue seed coats. Botanically speaking, these blue structures are seeds, not fruits. A fruit is the seed-bearing structure in flowering plants that is formed from the ovary after the plant flowers, while seeds are formed from ovules, the structure that contains female reproductive cell of plants. Because the ovarian wall of a Blue Cohosh flower is shed during the early phases of seed development, the fruit can be considered a “naked” seed.
We think of gymnosperms (conifers, cycads, ginkos) as having naked seeds, lacking both flowers and ovaries, and flowering plants as typically having ovaries which develop into seed-containing fruits. The exposure of the seeds as in Blue Cohosh is an unusual condition for flowering plants. By bearing its seeds openly, Blue Cohosh is vulnerable to predators that would eat the seeds. The plant counteracts this vulnerability with the toxicity of its seeds, which are poisonous to many species including humans, under certain circumstances. (St. Olaf College Natural Lands)
Blue Cohosh, one of our early spring wildflowers, has diminutive flowers that open before its leaves fully expand. Like Wild Ginger, Blue Cohosh flowers are the color of rotting meat, which may account for the fact that flies are its main insect visitors. Flies tend to feed at a single flower until satiated, which is not conducive to cross-pollination, and thus most fertilization in Blue Cohosh is the result of self-pollination.
Native Americans treated a wide range of afflictions with Blue Cohosh, including gallstones, fevers, toothaches and rheumatism. The most common use of its rhizomes, or underground stems, was as an aid to speed and ease childbirth. Even today it still serves this purpose — 64% of midwives surveyed reported using Blue Cohosh to treat women before or during childbirth. It has, however, had deleterious effects on some women and has not been evaluated by the FDA.