Sundews are named for the reddish glandular hairs that cover their leaves, each of which terminates in a large, sticky, dew-like drop that glistens in the sun.
If not for these red, gland-tipped hairs, Minnesota's four native sundews might be overlooked. When sundews form dense colonies in sunny settings, their bright, dewy hairs appear as patches of tiny sparkling rubies within a sea of green sphagnum moss.
The leaves of all Minnesota sundews are arranged in a basal rosette. The size and shape of the leaf blade distinguish one species from another. Linear-leaved sundew (Drosera linearis Goldie) has the longest (½ inch to 2 inches) and narrowest leaves. English sundew (D. anglica Hudson) has leaves ranging from ½ inch to nearly 1½ inches long that are broader toward the tips. The leaves of spatulate-leaved sundew (D. intermedia Hayne) are similar to those of English sundew, but slightly smaller and more vertically separated along the stem, giving the plant a leafier and more upright appearance. Round-leaved sundew (D. rotundifolia Linnaeus) is the smallest of the four species, with leaves less than ½ inch long, terminating in a circular shape.
All Minnesota sundews have an arrangement of tiny white flowers that grow on one side of a slender, leafless stem. The flowering stem is tightly coiled as it emerges from the center of the leaves, unfurling as it matures. Flowers open in mid- to late summer.
Habitat and Range.
Round-leaved sundew is the most common sundew in Minnesota and the most broadly distributed across North America, Europe, and Asia. It can be found in forested swamps or bogs under black spruce, cedar, or tamarack trees, as well as in sunny, open fens, where it prefers mossy hummocks. Spatulate-leaved sundew prefers the wetter environment of open fens or the margins of bog ponds, often growing in shallow water. English and linear-leaved sundews are much rarer, and both are species of special concern in Minnesota. Both occur almost exclusively in open rich peatlands, and often in water track fens, within the interiors of large patterned peatlands.
Like all carnivorous plants, sundews have leaves that catch, digest, and absorb insect prey for their nutrients. The insects are attracted to the hairs that cover the leaves, each one tipped with a glistening drop of sugary, sticky mucilage. A visiting insect's movement triggers the hairs, which respond to the slightest stimuli, to entangle the insect. As it struggles, it touches more of the sticky drops, trapping it against the leaf, which secretes digestive enzymes that dissolve its soft tissues. Some sundews curl their leaf blades in order to maximize contact with the entrapped prey.
Sundews have evolved their carnivorous habits in response to the limited supply of nutrients in their wet, fairly acidic habitats. The plants capture a diversity of small insects to supplement their nutrient needs throughout the growing season, with peak activity before flowering begins.
All of our sundews reproduce from seeds. Sundews' most common pollinators include several fly species and occasionally small bees. Spatulate-leaved sundew is also able to reproduce vegetatively, developing new plantlets from portions of the flowers.
History and Status.
Approximately 170 sundew species, which vary greatly in size and shape, occupy temperate and tropical habitats throughout the world. Charles Darwin was captivated by carnivorous plants. In his 1875 book Insectivorous Plants, he writes extensively about round-leaved sundew, the focus for much of his research.
Erika Rowe, DNR botanist