Sagina nodosa ssp. borealis Crow
Click to enlarge
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.
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.
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.
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.
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.