Sagina nodosa ssp. borealis    Crow

Knotty Pearlwort 


MN Status:
endangered
Federal Status:
none
CITES:
none
USFS:
none

Group:
vascular plant
Class:
Dicotyledoneae
Order:
Caryophyllales
Family:
Caryophyllaceae
Life Form:
forb
Longevity:
perennial
Leaf Duration:
deciduous
Water Regime:
terrestrial
Soils:
rock
Light:
full sun
Habitats:

(Mouse over a habitat for definition)


Best time to see:

 Foliage Flower Fruit 
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Sagina nodosa ssp. borealis Sagina nodosa ssp. borealis

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Map Interpretation

Map Interpretation

  Synonyms

Sagina nodosa var. borealis

  Basis for Listing

Sagina nodosa ssp. borealis is a low, tufted or matted perennial characteristic of sea cliffs on rocky shores and bays on the Atlantic Coast of North America. Occasional inland occurrences are found on the shores of large, subarctic lakes in Canada, as well as the shores of Hudson Bay, Lake Manitoba, and Lake Superior (Crow 1978; Porsild and Cody 1980). This scattered distribution pattern has no simple explanation but is probably a result of the glacial history of North America. According to Crow (1978), the ability of S. nodosa ssp. borealis to colonize cold, rocky shores and gravel beaches made it well adapted to habitats that were common during Pleistocene glaciation, and it is now confined to the relatively few places where periglacial-like conditions still exist. The current populations are likely relicts of an earlier, more widespread distribution. However long S. nodosa ssp. borealis has been at this latitude, it is clearly restricted to places that are too harsh for most temperate-climate plants to tolerate.

In Minnesota, S. nodosa ssp. borealis occurs in a few locations along the rocky shores of Lake Superior. Prior to 2000, it was known only from Cook County. But in 2000, the Minnesota Biological Survey discovered two new locations in Lake County. Botanists also confirmed one of the Cook County sites in 1998. The native North American populations of S. nodosa have been segregated by Crow (1978) as the subspecies borealis. The typical subspecies is apparently native to Europe with a few adventive populations on the Atlantic Coast of North America. Sagina nodosa ssp. borealis was listed as an endangered species in Minnesota in 1984.

  Description

There is no other species in Minnesota that could be easily confused with S. nodosa ssp. borealis based on a few readily visible features. The plant itself is a low, tufted, mat-forming perennial. The lower leaves are triangular in cross-section and taper to a point. Upper leaves are paired and scale-like. At the base of some leaf-pairs there may be a tiny, sterile (non-flowering) shoot. The small, delicate, white flowers have 5 petals, each about twice as long (4 mm (0.16 in.)) as the tiny sepals (2 mm (0.08 in.)). Flowers are borne singly at the ends of slender branches. Capsules produce several black seeds that have a pebbly-textured surface.

  Habitat

In Minnesota, this subarctic species is known to occur only along the shore of Lake Superior. It is rooted in rock crevices within about 3 m (10 ft.) of the lake, where it is sometimes subjected to spray from waves, but in settings where it is not exposed to direct wave action or severe ice-scouring. The crevices are in rhyolite (in/near calcite veins), slate, and basalt. The rocky habitats surrounding the crevices are typically bare, have some mosses and crustose lichens, or support a few other small plant species such as Campanula rotundifolia (harebell) and Primula mistassinica (Mistassinica primrose). Typical populations of S. nodosa ssp. borealis in Minnesota are composed of isolated tufts or clumps ranging from 10 to over 100 stems in number.

  Biology / Life History

Sagina nodosa ssp. borealis is a low-growing, mat-forming, perennial plant. Speculatively, these seeds would fall from the ripened fruit capsule and lodge among mineral grains in a rocky crevice, be eaten, or carried off by birds, wind, or water. Sagina nodosa ssp. borealis flowers late June to early August and fruits develop in August.

The best time to search for S. nodosa ssp. borealis is from mid-June to mid-July when it is in flower. With careful searching, this plant can be found until the end of the season and distinguished by vegetative features.

  Conservation / Management

Of the sites at which S. nodosa ssp. borealis has been confirmed since 1998, two are on private land and one site has uncertain ownership or management status. Even in protected areas, rocky habitats are often in some danger of inadvertent disturbance because people are attracted to rocks for recreation. It may be most beneficial for long-term conservation to increase the awareness of the concentration of rare features on Minnesota's beautiful, but fragile, Lake Superior shoreline. Populations of S. nodosa ssp. borealis are threatened by increasing numbers of herring gulls (Larus argentatus) that nest on the bedrock islands and shores, often upslope from plant occurrences. The high concentration of gull droppings that result in excessive nutrient enrichment, as well as direct trampling by birds cause the elimination of most native shoreline plants. At least one S. nodosa ssp. borealis population is located alongside a herring gull nesting colony.

  Conservation Efforts in Minnesota

A thorough, nearly-complete inventory by the DNR Minnesota Biological Survey has been accomplished for rare plants along much of Minnesota's North Shore of Lake Superior, which is a great contribution to conservation. Botanists agree that potential locations of this species have been well documented except for a small portion of Cook County. While the discovery of new populations is possible, it is unlikely there will be many more because of the exceedingly limited amount of suitable shoreline habitat. The survey results increase our knowledge of this species status and establish a sound basis for developing conservation plans.

  References

Crow, G. E. 1978. A taxonomic revision of Sagina (Caryophyllaceae) in North America. Rhodora 80:1-91.

Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. Second Edition. New York Botanical Garden, Bronx, New York. 910 pp.

Porsild, A. E., and W. J. Cody. 1980. Vascular plants of the continental Northwest Territories of Canada. National Museum Natural Sciences, National Museums Canada, Ottawa, Ontario, Canada. 667 pp.