Wildflowers of the Adirondacks:
Roundleaf Sundew (Drosera rotundifolia)
Roundleaf Sundew (Drosera rotundifolia L.) is tiny insectivorous wildflower which grows in acidic wetlands in the Adirondack Mountains and throughout New York State. It is a member of the Sundew (Droseraceae) family.
The term "droseros" is Greek for "dewy" and refers to the moist, glistening drops on the leaves, to which small organisms stick. The term "rodundifolia" comes from the Latin, meaning "round leaves." Other common names for the plant include Common Sundew, Round-leaved Sundew, and Round-leaf Sundew.
The Roundleaf Sundew is among a specialized group of bog plants that trap insects.
- The high acidity which characterizes the bog environment discourages the growth of fungi and bacteria, retarding decomposition and creating a chronic shortage of the mineral nutrients, such as nitrogen, that plants need for growth and reproduction.
- Insectivorous plants such as sundews, bladderworts, and the Pitcher Plant, consume insects as a supplemental source of nitrogen. This allows such plants to survive on nutrient-poor soils. The increased consumption of nitrogen from insect prey benefits plant growth, flowering, and seed production.
The extent to which Roundleaf Sundew depends on its insect prey for nutrition depends on the site. Studies have shown that the proportion of nitrogen derived from carnivory varies from about a quarter to about half. Reliance on carnivory is highest in nutrient-poor, open habitats. On shadier sites, under more nutrient-rich conditions, the Roundleaf Sundew reduces its investment in carnivory.
Identification of Roundleaf Sundew
The Roundleaf Sundew is a small plant, growing from two to ten inches high. The root system is usually shallow and consists of a taproot.
The rosette of basal leaves provides the primary key to identification.
- The leaves are small and round (about ¾ inch across).
- The upper surfaces are covered with reddish, glandular hairs, each tipped with a clear, sticky secretion that glistens in the sun.
- The green or red leaf stalks are flat, ½ to 2 inches long, and covered with fine hairs.
- The leaves generally lie flat or nearly flat against the ground.
A similar species Spatulate-leaved Sundew (Drosera intermedia) also grows in our area, but it has spoon-shaped flowers, and its leaf stalks lack hairs.
Roundleaf Sundew's leaves are adapted to catch and consume insect prey.
- Insects are trapped by the sticky droplets at the tip of the longer, outer tentacles. The plant responds by folding the tentacles around the prey. Plant response depends on what is being devoured, with more rapid response when the victim is actively struggling.
- The prey is digested when the shorter hairs on the inner surface of the leaf secrete a mucilage containing digestive enzymes and an anesthetic that debilitates the prey.
- The captured insect becomes digested into soluble materials that are absorbed into the leaf cells and later distributed to other parts of the plant.
- Midges and other small flies reportedly constitute Roundleaf Sundew's main prey.
The role of the distinctive red color of the leaves is unclear. One hypothesis is that it is designed to attract insects. However, this theory has not been supported by experiments.
The flower of the Roundleaf Sundew is small and white (sometimes pinkish), occurring at the end of a long, leafless stem rising above the leaf rosette. The flowers are about ¼ inch wide, with five petals and five tiny sepals. The flowers grow in one-sided clusters. The flowering stem is tightly curled and unfurls as the flowers bloom.
In the Adirondack region, Roundleaf Sundews usually bloom in July of early August. A tally of flowering dates for the upland Adirondack areas compiled by Michael Kudish, based on data collected from the early seventies to the early nineties, lists the bud date as 17 July and the flower date as 4 August.
The fruit of Roundleaf Sundew consists of capsules with many small, light brown seeds. Seeds may be distributed by flowing water, wind, the feet or feathers of birds, or mammals' fur.
Uses of Roundleaf Sundew
Roundleaf Sundew appears to have limited edible or medicinal use in the US. Native American groups reportedly made little use of this plant.
Historical accounts suggest that Roundleaf Sundew has been used in the past in Europe as a herbal remedy for a variety of ailments, including warts, chronic bronchitis, asthma, and whooping cough. For instance, a tincture of the plant was said to be used for dry, spasmodic coughs; a poultice of plant juice was reportedly used on corns and warts. Harvesting of the plant for use in European herbal medicine has raised conservation concerns.
Wildlife Value of Roundleaf Sundew
Roundleaf Sundew has minimal food or cover value in our area, although the wetland habitats that host them are important breeding areas for boreal birds, such as the Palm Warbler and Lincoln's Sparrow. The plant may be an important food source for bog-dwelling ants, who reportedly scavenge up to two-thirds of the prey caught by the plant.
Distribution of Roundleaf Sundew
Roundleaf Sundew is generally cirumboreal, found in all of northern Europe and much of Siberia. In North America, it grows in the eastern half of the United States and throughout Canada.
- Roundleaf Sundew occurs south along the Pacific coast to California and inland as far as western Montana and western Colorado.
- In the East, round-leaved sundew is found from Nova Scotia south to Georgia, Florida, and Alabama and west to the Mississippi River, Iowa, and Minnesota.
- This plant is listed as Endangered in Illinois and Iowa, Threatened in Tennessee, and Exploitably Vulnerable in New York.
In New York State, Roundleaf Sundew may be found in most counties in the northeastern part of the state. It is found in all Adirondack Park Blue Line counties except Clinton and Warren counties.
Habitat of Roundleaf Sundew
Roundleaf Sundew is an obligate wetland species, meaning that it is generally restricted to sites that provide continually moist or wet situations. Roundleaf Sundew is most often found in acidic bogs, but can also be seen growing in swamps or on rotting logs, mossy crevices, pond, lake, and stream margins, and floating sphagnum mats or hummocks. Roundleaf Sundew prefers full sun, but can survive in limited shade.
In the Adirondack Mountains, Roundleaf Sundew is found in several ecological communities:
In Inland Poor Fens, for instance, look for Roundleaf Sundew growing on sphagnum. Characteristic shrubs in this ecological community include Bog Laurel, Sheep Laurel, Leatherleaf, Bog Rosemary, and Labrador Tea. There may be scattered stunted trees, such as Tamarack and Black Spruce. Characteristic herbs growing near Roundleaf Sundew include Rose Pogonia, Grass Pink, and Pitcher Plant.
A convenient place in our area to find Roundleaf Sundew is on Barnum Bog at the Paul Smiths VIC, where it may be viewed from the boardwalk on the Boreal Life Trail. It can also be found growing on the decaying trunks of trees lying in the water along the shores of area ponds and in the peat moss of alpine bogs at high elevations.
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