Saxifraga paniculata    P. Mill.

Encrusted Saxifrage 


MN Status:

threatened
Federal Status:
none
CITES:
none
USFS:
yes


Group:

vascular plant
Class:
Dicotyledoneae
Order:
Rosales
Family:
Saxifragaceae
Life Form:
forb
Longevity:
perennial
Leaf Duration:
deciduous
Water Regime:
terrestrial
Soils:
rock
Light:
full shade, partial shade
Habitats:

(Mouse over a habitat for definition)


Best time to see:

  Foliage   Flower   Fruit  
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Saxifraga paniculata Saxifraga paniculata Saxifraga paniculata Saxifraga paniculata

Click to enlarge


Map Interpretation

Map Interpretation

  Synonyms

Saxifraga aizoon var. neogaea

  Basis for Listing

This arctic-alpine species occurs from the arctic regions of northeastern North America south to rocky areas in northern New England and in rocky places in the Lake Superior region. Saxifraga paniculata also occurs across the North Atlantic in Iceland, Greenland, and Norway. Its distribution differs from other amphi-Atlantic arctic-alpine species by occurring in central and southern Europe and in the Caucasus (Voss 1985). There are several varieties of the species in Europe. The populations in Greenland, Iceland, and North America are usually referred to as variety neogaea (Butters 1944).

Saxifraga paniculata has an unusual history of discovery in Minnesota. From 1932 to 1993, it was only known from the northern border of Cook County. The 1930s marked a period when Fredrick Butters and Ernst Abbe (1953) were researching the flora of Cook County, aided by such notable field botanists as Murray F. Buell, G. W. Burns, and M. J. Hendrickson. Little additional work was done in that region until the 1980s when Minnesota DNR and U.S. Forest Service professionals attempted to relocate historic collection sites of rare plants and assess their status. Between 1980 and 1984, 9 of the 11 historical sites for S. paniculata were relocated and 2 additional populations were found.

Ten years later, in 1994, a large but localized population of S. paniculata was found in Lake County, the first time the species was found outside of Cook County. With additional inventory efforts a few years later, Minnesota Biological Survey botanists found about 10 new populations in Lake and Cook counties, all on or near the North Shore of Lake Superior. The North Shore locations probably weren't discovered until recently because this species wasn't targeted or expected in earlier studies, it can occur in fairly inaccessible or dangerous locations, and sites are often on private land.

Currently, the known populations of S. paniculata contain from 10 to over a 1,000 individuals, typically in scattered small or large patches on rocky ledges and crevices on steep cliffs. Only a few populations have been observed repeatedly over successive years because of the difficulty accessing some of the sites, so it is not possible to estimate any overall trends in population sizes. Saxifraga paniculata was listed as a threatened species in Minnesota in 1984.

  Description

Saxifraga paniculata is a perennial herb that is most easily and reliably identified by its distinctive basal rosette of leaves. Leaves are 2-3 cm (0.8-1.2 in.) long, and stiff, with margins finely and densely toothed. At the base of each tooth is a white, lime-encrusted pore, hence the common name of the plant. Rosettes of S. paniculata grow at the ends of long, horizontal stolons (runners). The flowering stem may rise 10-30 cm (4-12 in.) in height and display most of the small white flowers near the top. Each flower has 5 white petals, 1 inferior ovary, 2 styles, and a 2-beaked capsule.

  Habitat

In Minnesota, S. paniculata typically occurs in rock crevices and on small ledges on shady cliffs that generally face northward. The crevices in which the plants are rooted may be fairly dry. In some places the plants are in thin gravelly soil on uppermost ledges, sometimes in full sun for a portion of the day. Most plants are in more mesic portions of a particular cliff. The general bedrock types may be diabase, gabbro/diorite, basalt, or Rove Formation rocks (shale, argillite, greywacke), but there may be localized mineral concentrations in cracks and crevices in which the plants are rooted. Associated plant species include Aquilegia canadensis (columbine), Campanula rotundifolia (harebell), Carex eburnea (ivory sedge), and Woodsia glabella (smooth woodsia).

  Biology / Life History

Saxifraga paniculata is an herbaceous, perennial plant that forms basal rosettes and an erect flower stalk. Leaves are stiff but not evergreen. New shoots are produced in late summer next to the previous year's rosettes, and they turn green quite early. Plants begin to produce new stolons and rosettes in the spring. Stolons allow this plant to spread vegetatively. Flowers are perfect, having both male and female parts. Plants begin flowering in June and fruits usually begin maturing in late July or early August.

The best time to search for S. paniculata is when it flowers, from early June to July, and when it fruits, from late July through August. Rosettes can be seen anytime during the growing season and even through the winter, though they lose most of their green color.

  Conservation / Management

Like the other rare, arctic-alpine plants in Cook and Lake counties, S. paniculata has a very limited amount of suitable habitat in which it can survive. Only about half of Minnesota's North Shore populations happen to be on public land in federal or state ownership; many important populations are on privately owned land. Recreational rock climbing is one of the few human activities that directly threaten this species. Indirect impacts could come from changing habitat conditions due to global climate change.

  Conservation Efforts in Minnesota

A fairly thorough inventory by the DNR Minnesota Biological Survey has been completed for rare plants along Minnesota's North Shore of Lake Superior and in portions of the Border Lakes Ecological Subsection, which includes the Boundary Waters Canoe Area Wilderness. It is possible that additional locations of S. paniculata may be found in the Border Lakes Subsection before the survey is complete. The potential discovery of new populations does not alter the need for conservation of this species because of the exceedingly limited amount of suitable habitat.

  References

Butters, F. K. 1944. The American varieties of Saxifraga aizoon. Rhodora 46:61-69.

Butters, F. K., and E. C. Abbe. 1953. A floristic study of Cook County, northeastern Minnesota. Rhodora 55:21-201.

Voss, E. G. 1985. Michigan Flora. Part II: Dicots (Saururaceae-Cornaceae). Cranbrook Institute of Science Bulletin 59 and the University of Michigan Herbarium. University of Michigan, Ann Arbor, Michigan. 727 pp.