A small, flattened and fairly inconspicuous shrub (3) (4), the dwarf bilberry (Vaccinium cespitosum) grows in low, dense, circular mats that may spread for several metres (2) (4) (5) (6). It is a perennial species (7), with branching, angled twigs that are yellow-green, reddish-green or reddish-brown, sometimes covered in a greyish, bluish, or whitish waxy coating (2) (6).
The small, deciduous leaves of the dwarf bilberry are alternately arranged along the stem and are somewhat paddle-shaped, being narrow and tapered at the base and becoming wider and more rounded towards the top (2) (3) (4) (5) (7). The edges have fine, bristle-tipped teeth (3) (4) (5). The upper surface of the leaves is bright green and smooth, while the underside is paler and has a number of simple glands (2).
The dwarf bilberry produces small, usually pinkish, bell-shaped flowers which are attached singly in the leaf axils (2) (3) (4) (5) (6). The small round berries of this species are blue to dark blue or blackish, sometimes with a whitish waxy coating (2) (3) (4) (6). The berries contain small brown seeds (2).
- Also known as
- dwarf blueberry, dwarf huckleberry, dwarf whortleberry.
- Vaccinium caespitosum.
- Height: 5 - 50 cm (2)
Dwarf bilberry biology
The dwarf bilberry is an important host plant for the larvae of the rare northern blue butterfly (Plebejus idas) (3) (4) (5) (8). The butterfly lays its eggs on the stems of the dwarf bilberry in late summer and autumn, and the eggs hatch the following spring. The caterpillar of the northern blue butterfly feeds on the dwarf bilberry until it pupates and emerges as an adult butterfly (9).
Flowering occurs in late May to early July (2) (4), and the flowers are primarily pollinated by bees (9). Fruits are produced and begin to mature immediately after flowering, becoming fully ripe by late summer or early autumn (2) (4) (6) (9). The berries of the dwarf bilberry are an important food source for many North American birds and small mammals, while plants in the Vaccinium genus are also known to form an extremely important dietary component of both brown (Ursus arctos) and black (Ursus americanus) bears (2).
The dwarf bilberry reproduces by creeping horizontal plant stems, called stolons, which take root at points along the stem to form new plants. As a result, the dwarf bilberry typically forms large, dense, spreading mats, although each large colony only actually consists of one or a few individual plants (4).
Dwarf bilberry range
The dwarf bilberry occurs in North America, ranging from Alaska to Labrador in the north, and extending south to Newfoundland, New Brunswick, New England, Michigan, Minnesota and Wisconsin. It also occurs in the western mountains as far south as Colorado and California (2) (4).
Dwarf bilberry habitat
Occurring mainly in open or semi-open habitats, the dwarf bilberry is typically found on areas of dry, sandy soil up to elevations of 4,500 metres. It is frequently found in the dry northern forests and dry sand prairies, as well as in seasonally wet meadow-like areas (4) (5) (6) (8).
The dwarf bilberry occurs as an understory species in coniferous forests. It may also occur in alpine heath habitats (2), along or near former railroads, along shoreline trails and among mossy rocks or rocky, gravelly or sandy clearings along riverbanks (4). This species commonly grows on moist subalpine or alpine slopes and on mossy forest floors, where it will form a low, nearly continuous layer of vegetation (2).
Dwarf bilberry status
The dwarf bilberry has yet to be assessed by the IUCN.
Dwarf bilberry threats
The dwarf bilberry is considered rare or threatened in many parts of its range, largely because its habitat has been severely degraded and diminished (5). Further habitat disturbance remains a threat to the dwarf bilberry (4).
Changes in management practices and fire suppression have resulted in the loss of many areas of suitable habitat for the dwarf bilberry in recent years (9). This species thrives in open and semi-open habitats, and the encroachment of dense vegetation and woody plants is therefore a major threat to existing populations (4) (9). Non-native species, such as invasive grasses and weeds, may also impact dwarf bilberry populations through competition for space and resources (9).
Dwarf bilberry conservation
The dwarf bilberry occurs on State and National Forest lands throughout its range, affording it some level of legal protection (4) (9).
Management and conservation of the dwarf bilberry is particularly important because of its critical role in the life cycle of the northern blue butterfly. Recommended conservation measures include avoiding and reducing levels of habitat disturbance to the dwarf bilberry, while its habitat should be carefully managed by thinning and controlled burning of vegetation in order to prevent encroachment by other plants (4). At smaller sites, where fires presents a high risk to butterfly eggs, larvae, and pupae, manual removal of trees and dense ground vegetation is recommended (9).
A systematic monitoring programme should be introduced for both the dwarf bilberry and the northern blue butterfly, and the results should be used to inform suitable conservation measures and enable land managers to implement long-term management activities (9). Further research is needed into the impact of climate change and non-native species on the dwarf bilberry’s population (9).
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- The angle between the upper side of a leaf or stem and the supporting stem or branch.
- A plant that sheds its leaves at the end of the growing season.
- A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
- An organ that secretes substances used by the plant, such as hormones, enzymes, waxes, nectar, salt and water.
- Immature stage in an animal’s lifecycle, after it hatches from an egg and before it changes into the adult form. Larvae are typically very different in appearance to adults; they are able to feed and move around but are usually unable to reproduce.
- A plant that normally lives for more than two years. After an initial period, the plant usually produces flowers once a year.
- The process of becoming a pupa, the stage in the life cycle of some insects during which the larval form is reorganised into the adult form. The pupa is usually inactive, and may be encased in a chrysalis, cocoon or other protective coating.
ITIS (February, 2012)
USDA Forest Service: Fire Effects Information - Dwarf bilberry Vaccinium caespitosum (February, 2012)
University of Wisconsin-Green Bay Herbarium - Dwarf bilberry Vaccinium caespitosum (February, 2012)
Michigan Natural Features Inventory - Dwarf bilberry Vaccinium caespitosum (February, 2012)
Michigan Natural Features Inventory: Rare Species Explorer - Dwarf bilberry Vaccinium caespitosum (February, 2012)
Flora of North America - Dwarf bilberry Vaccinium caespitosum (February, 2012)
Robert W. Freckmann Herbarium, University of Wisconsin-Stevens Point - Dwarf bilberry Vaccinium caespitosum (February, 2012)
Wisconsin Department of Natural Resources - Dwarf bilberry Vaccinium caespitosum (February, 2012)
Wolf, A.T and Brzeskiewicz, M. (2002) Conservation Assessment for Northern Blue Butterfly - Plebejus (Lycaeides) idas nabokovi (Masters) and Dwarf Bilberry - Vaccinium caespitosum (Michx). USDA Forest Service, Eastern Region, Milwaukee, Wisconsin. Available at: