Androsace septentrionalis ssp. puberulenta
Basis for Listing
Androsace septentrionalis is wide ranging in North America including far northern latitudes. It is known as an alpine and subalpine wildflower in the Rocky Mountains and as a dry prairie species on the northern Great Plains. In Minnesota it appears to be restricted to dry prairie or prairie-like habitats in the northwest corner of the state, and it seems to be very rare.
The prairie affinity of A. septentrionalis is demonstrated by its need for loose, sandy soil in full sunlight, usually where there is little competition from other plants. On a few occasions small numbers of plants have been found in abandoned gravel pits and other human-created habitats, which seem to satisfy at least some of the species' habitat needs. However, the best habitats, and possibly the only habitats that are able to support viable populations, seem to occur on glacial beach ridges in dry prairie remnants. It is unclear if current conservation practices and land management activities in the northwest corner of the state are adequate to assure the long-term survival of this species in Minnesota.
The most recent taxonomic revision of the genus Androsace concluded that A. septentrionalis consists of six distinct subspecies (Robbins 1944). Based on that treatment, it appears the only subspecies occurring in Minnesota is subspecies puberulenta. A more recent assessment that falls short of a complete revision chose to treat the species as a highly variable complex and did not designate subspecies (Kelso 2009). The taxonomic debate might influence the name that we use for this plant in Minnesota, but it does not influence the conservation needs. Androsace septentrionalis was listed as a special concern species in Minnesota in 1996.
Androsace septentrionalis is an annual or a short-lived perennial with a rosette of small, narrow leaves 1-3 cm (0.4-1.2 in.) long. There is no leafy stem in the obvious sense of the word, but there are 1 or more naked flowering stems 1-10 cm (0.4-3.9 in.) long, each with an umbel of 5-20 small flowers at the tip. Each flower has 5 white petals.
According to Robbins (1944), subspecies puberulenta differs from the other subspecies in that it has more than 1 equally developed stem, puberulent leaves, and narrowly triangular calyx lobes. Only subspecies puberulenta is known to occur in Minnesota.
A similar relative, A. occidentalis, is common and widespread in Minnesota. In A. septentrionalis, the small bracts at the base of each umbel are relatively narrow and lanceolate to linear-lanceolate in shape. In contrast, the bracts of A. occidentalis are relatively broad and ovate to lanceolate in shape.
All of the records of A. septentrionalis from Minnesota are from sparsely vegetated, sunny habitats in dry, sandy soil. The sites are within prairies or at least within the prairie region of the state. Most are on glacial lake beach ridges, but a few are from other sandy habitats, including river banks, abandoned gravel pits, and gravelly roadsides.
Biology / Life History
Androsace septentrionalis is described variously as an annual, a biennial, and a short-lived perennial. It has also been described as a winter annual, which means the seeds germinate in the fall, and the plant overwinters as a small rosette. When the snow melts in the spring, the rosettes resume growth before producing an inflorescence (Inouye et al. 2003). It is possible that the species behaves differently in different parts of its range or in different habitats. How the species behaves in Minnesota is unknown.
The flowers of A. septentrionalis are known to be insect-pollinated, though it is not known what type of insect acts as a pollinator in Minnesota. A small syrphid fly and a small solitary bee were observed visiting flowers during a study of this species in Colorado (Inouye 2003).
The plants are shallowly rooted in sandy soil that typically has poor water holding capacity. This results in fluctuations in surface soil moisture, which in turn appears to cause fluctuations in flowering and fruiting success (Inouye et al. 2003). Flowering often starts early in the spring while there is still moisture in the soil from snow melt. By July, the soil moisture is typically quite low and the plants cease to flower and may die before the seeds are mature. If there is adequate rain in July, the plants survive to produce seeds and may even flower for the second time that year (Inouye et al. 2003).
A healthy population of A. septentrionalis apparently maintains a seed bank in the soil. This enables the population to survive periods of drought when no seeds are produced. It also allows the population to respond quickly to soil disturbances that expose unvegetated soil where there is little competition. In this scenario, the seeds would germinate quickly and complete an entire life cycle in only a few months, thereby replenishing the seed bank before competition becomes too intense. Even small-scale disturbances such as pocket gopher mounds may provide needed microhabitats (Laycock 1958). This ability to rapidly complete an entire life cycle is the likely explanation for how this species manages to appear in cultivated farmland in western Canada, at least in situations where zero-tillage is practiced (Blackshaw 2003).
An experiment in a dry prairie in southwestern Alberta, Canada determined that cattle grazing eliminated A. septentrionalis from the vegetation plots that were studied, but it did survive in the soil seed bank (Willms and Quinton 1995). Minnesota prairies have a different floristic composition so it is not known how these results might be applied here.
Since the phenology of A. septentrionalis is dependent on the progression of spring and on the timing and amount of rainfall, it is difficult to predict the best dates to search for this species. In an average year flowering will begin around the middle of May and last until the middle of June.
Conservation / Management
It seems likely that A. septentrionalis needs a fairly large area of habitat, or at least an interconnected network of habitats, in order to maintain a long-term presence in Minnesota. Although a large area of habitat would not be fully occupied by the species, a large extent of habitat might be needed to maintain a variety of microhabitats that this species apparently requires. Such microhabitats may include naturally occurring things like pocket gopher mounds, the area around badger dens, and wind-eroded ridge-tops. This is a classic example of a metapopulation where a large stable population is actually composed of numerous small transient colonies. Although each colony may be short-lived, the population might be able to endure a very long time.
Androsace septentrionalis plants have also been found in abandoned gravel pits and other temporary habitats created by human activities. Such ruderal habitats may have a role to play in the metapopulation concept. However, the appearance of appropriate ruderal habitats is unpredictable. For that reason, their conservation value is limited and can probably be discounted from management considerations.
Several programs and resources are available to land managers and landowners to help protect and manage remaining prairie parcels including the Native Prairie Bank Program, the Native Prairie Tax Exemption Program, and a prairie restoration handbook.
Conservation Efforts in Minnesota
An occurrence of A. septentrionalis has been reported from Lake Bronson State Park, and from two state Wildlife Management Areas. However, the condition and status of these occurrences are currently unknown.
Blackshaw, R. E. 2003. Soil temperature and soil water effects on pygmyflower (Androsace septentrionalis) emergence. Weed science 51:592-595.
Inouye, D. W., F. Saavedra, and W. Lee-Yang. 2003. Environmental influences on the phenology and abundance of flowering by Androsace septentrionalis (Primulaceae). American Journal of Botany 90(6):905-910.
Kelso, S. 2009. Androsace. Pages 259-263 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 8. Oxford University Press, New York, New York.
Laycock, W. A. 1958. The initial pattern of revegetation of pocket gopher mounds. Ecology 39(2):346-351.
Robbins, G. T. 1944. North American Species of Androsace. The American Midland Naturalist 32:137-163.
Wilms, W. D., and D. A. Quinton. 1995. Grazing effects on germinable seeds on the fescue prairie. Journal of Range Management 48:423-430.