Synonyms

Pinguicula vulgaris var. americana

  Basis for Listing

Pinguicula vulgaris is a circumboreal plant. In North America, it ranges from Newfoundland to Alaska, south to northern New England, and westward to northeastern Minnesota. In Minnesota, it is only known to occur on the shores of Lake Superior. One of the earliest collections in Minnesota was made in 1886 by E. P. Sheldon from the rocky shores of Lake Superior near Two Harbors. The species remained rather poorly documented in the state until intensive botanical surveys were conducted in the North Shore Highlands. Since these surveys began in 2000, 21 additional occurrences have been documented. As of 2009, approximately 50 locations had been documented in the state, all within Lake and Cook counties.

The habitat of P. vulgaris is not only restricted to Lake Superior shores, but further confined to a small portion of tiny pools, seepy cracks, and ledges that occur even less frequently along the shoreline. Although these occurrences are scattered along the shore, a variety of them occur in relative proximity to each other and thus would be subject to a single catastrophic event. Another concern is global climate change, which could alter the cool, moist habitat conditions the species requires.

Pinguicula vulgaris is a species with very limited available habitat in Minnesota, and it is very dependent upon high quality conditions for survival. North Shore habitats continue to be lost and degraded by development and the impacts of recreational use. For these reasons, P. vulgaris was listed as a special concern species in Minnesota in 1984.

  Description

Pinguicula vulgaris is a small, insectivorous plant 4-15 cm (1.6-5.9 in.) tall. It is readily recognized by the flat-lying, basal rosette of 3-6 yellowish-green and often sticky leaves. Single, bluish-purple flowers occur on 1-9 bractless scapes (stalks). Flowers are 5 parted consisting of an upper lip (with 2 lobes) and a lower lip (with 3 lobes). The lower lip is prolonged into a long spur. Observation of the leaves typically displays numerous tiny insects and fine debris seemingly stuck to the leaf surface.

  Habitat

In Minnesota, P. vulgaris only occurs along the rocky shores and cliffs of Lake Superior. Known locations are all near the edge of the lake in habitats shaped and climatically influenced by the dynamics of Lake Superior. Habitats are often moist or seepy and include: cracks and fissures in lake shore bedrock; peaty, rimmed edges of bedrock pools; low-lying rock ledges; moist, seepy cliffs sheltered from storm waves; and bouldery lake shore meadows. Most populations occur in a zone that is directly influenced by storm waves, though the plants find some shelter persisting in cracks or tucked behind bedrock structures that provide limited protection from a wave's direct impact. Lake Superior provides cool, moist conditions and natural disturbance regimes that maintain a microclimate seemingly well suited to P. vulgaris. The species most commonly occurs on the extensive, slightly alkaline, basalt lava flows that line major portions of the Minnesota shoreline.

In Michigan, P. vulgaris is known from a diversity of habitats including the alkaline rocks and sands of Isle Royale and Pictured Rocks, and marly fens and rock outcrops inland from the Great Lakes (Voss 1996). In Wisconsin, the species is known from the sandstone cliffs of the Apostle Islands where it occurs on ledges and fallen boulders (Wisconsin DNR 2010).

Plant species growing in association with P. vulgaris include: Campanula rotundifolia (harebell), Lobelia kalmii (Kalm's lobelia), Primula mistassinica (Mistassini primrose), Euphrasia hudsoniana var. ramosior (Hudson Bay eyebright), Bistorta vivipara (alpine bistort), Solidago ptarmicoides (upland white aster), Trichophorum cespitosum (tufted bulrush), Carex lenticularis var. lenticularis (lenticular sedge), Deschampsia cespitosa ssp. cespitosa (tufted hair grass), and Trisetum spicatum (spike trisetum).  Primula mistassinica

  Biology / Life History

Plants reproduce sexually and are insect pollinated. Pinguicula vulgaris can also produce offshoots, which grow asexually into new adults. This may sometimes explain the appearance of rosettes closely crowded and overlapping each other. Like other members of Lentibulariaceae (bladderwort family), P. vulgaris is an insectivorous plant. Leaf surfaces contain two types of glands. Stalked glands are tipped with globular, mucilaginous (sticky) secretions and sessile glands release digestive enzymes. Small insects landing or crawling on the leaf surface become increasingly mired in the sticky, honey-like secretion, which stimulates the release of digestive enzymes. The prey gradually becomes pooled in digestive juices, and these nutrients (including phosphorus) are gradually absorbed into the leaf. It is also suggested that other nutrient rich substances, including pollen, are also digested and utilized by the plant. Leaves also produce a bactericide that retards the insects from rotting while they are being digested. This substance is reported to curdle milk and promote healing. Plants need to grow in moist, humid conditions because the pores in the leaf surface, which are needed to absorb digested nutrients, can also lead to undesired loss of moisture resulting in desiccation.

Minnesota occurrences of P. vulgaris range in number from several individuals to hundreds of plants. They typically occur in small patches of several plants to a couple dozen or more at a given microsite. Larger numbers are often associated with areas that provide a greater diversity and frequency of small pools and suitable habitat patches.

  Conservation / Management

Water levels in lake shore pools vary accordingly with rain and storm events, and water volume and quality are both directly affected by run-off. Geese, gulls, and other species loafing on the rocky shores contribute their feces, likely altering the water quality and chemistry of some small pools and seepy shoreline cracks. The nutrient enrichment and trampling associated with the numerous gull breeding colonies has an exceptionally deleterious effect on nearby shoreline vegetation, especially on the rock pools. Like the gulls (mainly ring-billed gulls (Larus delawarensis)), the number of geese along the North Shore has increased and they are known to graze the scant vegetation along the rocky shore and pools. The combined effects of increased grazing and localized pollution could well be a serious threat to some P. vulgaris populations. Additional threats include any activities that result in habitat degradation, increased competition, and alteration of water levels or water quality. Pinguicula vulgaris is a species with a very limited amount of available habitat in Minnesota, and it is very dependent upon high quality conditions for survival.

  Best Time to Search

The best time to search for P. vulgaris is when it is in flower from early June through late July, though plants have been reported flowering into early August. The distinctive yellow-green basal rosettes can be detected throughout much of the growing season and on into the fall.

  Conservation Efforts in Minnesota

Nearly 60% of the known occurrences of P. vulgaris occur on lands in private ownership. Only 13% are located within State Parks and just one occurrence (less than 2%) is in a Scientific and Natural Area. The remaining occurrences are on lands in tribal, state, or corporate ownership.

Some efforts are being made to encourage state park visitors to stay on designated trails. Scenic trails frequently occur near open shorelines where park visitors are tempted to leave the trail and explore and relax at the nearby shoreline. Although the bedrock appears to be nearly indestructible underfoot, the often sparse and patchy vegetation and associated native plant communities are very vulnerable to trampling.

  References and Additional Information

Voss, E. G. 1996. Michigan Flora. Part III: Dicots (Pyrolaceae-Compositae). Cranbrook Institute of Science Bulletin 61 and University of Michigan Herbarium, Ann Arbor, Michigan. 622 pp.

Wikipedia contributors. 2010. Pinguicula. Wikipedia, The Free Encyclopedia. . Accessed 02 February 2010.

Wisconsin Department of Natural Resources [WIDNR]. 2010. Common Butterwort (Pinguicula vulgaris) (Smith). . Accessed 02 February 2010.