Chrysosplenium iowense Rydb.
Iowa Golden Saxifrage
Basis for Listing
The Midwestern populations of this small saxifrage are thought to be relicts of the Pleistocene flora that survived the most recent glaciation in the unglaciated portion of southeastern Minnesota (The Blufflands and Rochester Plateau subsections) and northeastern Iowa. Although this refuge escaped glaciation, the habitats became cold and boreal-like. When the glaciers retreated 15,000 years ago, Chrysosplenium iowense (Iowa golden saxifrage) persisted in isolated pockets of habitat where cold microhabitat remained essentially unchanged. Because of the generally temperate climate of Minnesota and Iowa, the plants remain largely isolated in their refugia, unable to colonize surrounding habitats that are postglacial in origin. This explains why the nearest populations are hundreds of kilometers to the north in Manitoba, where true boreal habitats predominate and the species is not uncommon.
The populations of C. iowense in Canada are thought to have originated from a different glacial refugium that is now extinct (Levsen and Mort 2008). According to this theory, the Canadian populations have been separated from the Minnesota populations by at least 115,000 years, which explains the genetic differences between the populations seen in DNA analysis. The genetic differences may be great enough to consider the two populations as separate species (Levsen and Mort 2008). The recently discovered population in Banning State Park (Pine County; Mille Lacs Uplands Subsection) has not undergone genetic testing but is believed to have been derived from a singular long-range dispersal event from Minnesota or Iowa populations further south.
Chrysosplenium iowense is a very small inconspicuous plant. It will require very careful searching to find it and close inspection to correctly identify it. The leaves are opposite on the stem rather than alternate and simple rather than compound. Each leaf is roundish with shallowly but distinctly lobed margins. The flowers have 4 yellowish green sepals and no petals. The flowers are found in a small group of 3-12 at the very top of the plant, closely subtended by the uppermost leaves. They are quite small and visually inconspicuous. The fruit is a capsule with 20-30 minute seeds. The whole plant will be about 10 cm (4 in.) tall and will be growing in small stolon-linked clusters (Freeman 2009).
The only other member of this genus in Minnesota is C. americanum (American golden saxifrage). It differs from C. iowense by having opposite leaves rather than alternate and long decumbent stems rather than short upright stems.
In Minnesota, most C. iowense plants have been found on algific talus slopes associated with dolomite formations in the Galena geologic group. One location in Beaver Creek Valley State Park in Houston County is associated with the Prairie du Chien geologic group or the St. Lawrence Formation. The term algific means "cold producing"; such conditions result from cold air draining from ice caves in north-facing talus slopes. These slopes retain some periglacial features and are often quite restricted, as small as 1m² (10.8 sq. ft.). They support a habitat that is cool and moist all summer, with temperatures rarely exceeding 16 °C (61 °F). Algific talus slopes are highly localized phenomena within the unglaciated region in southeastern Minnesota and adjacent Iowa. This habitat is shared with several other relict boreal species, such as several endemic land snails and a variety of plants: Abies balsamea (balsam fir), Ribes hudsonianum (northern black currant), Rhamnus alnifolia (alderleaf buckthorn), Mertensia paniculata (panicled bluebells), Mitella nuda (naked miterwort), and Adoxa moschatellina (moschatel). Chrysosplenium iowense is often infrequent on the algific slope, but in some places it may be locally abundant. It often grows in carpets of mosses.
Biology / Life History
Chrysosplenium iowense behaves much like a spring ephemeral, emerging and flowering in early to mid-spring and often withering by mid-summer. The flowers are designed to be pollinated by small flying insects, though the transfer of pollen between flowers has not been witnessed. At maturity, the seed capsule is open on the top, exposing the seeds to drops of rainfall. This type of structure is sometimes called a “splash cup” because the splash from a single drop of water falling onto the cup propels seeds a surprising distance, resulting in significant, albeit short-distance, dispersal of the seeds. Long-distance dispersal must be a very infrequent and unpredictable event. Vegetative reproduction is accomplished by short ephemeral stolons that grow horizontally on the surface of the substrate.
Conservation / Management
Chrysosplenium iowense is very rare in this state, in part because suitable habitat is extremely limited and habitat alteration is a threat to the populations. Maintaining the boreal-like microhabitat conditions required by this species is key to plant survival. Some populations consist of only a few individuals and may not be viable. Even the largest population occupies less than 250 m² (300 sq. yd.) and is very susceptible to disturbance. Livestock grazing has degraded several populations. In addition to grazing, threats include trampling by hikers, removal of adjacent forest canopy, construction of roads, and disruption of the subterranean cold air and moisture system. An emerging challenge at a larger scale is that this species may suffer local habitat impacts from global climate change (Levsen and Mort 2008).
Best Time to Search
The best time to search for Chrysosplenium iowense is May through July.
Conservation Efforts in Minnesota
Welby R. Smith (MNDNR), 2020
(Note: all content ©MNDNR)
References and Additional Information
Freeman, C. C. 2009. Pyrola. Pages 378-384 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 8. Oxford University Press, New York, New York.
Levsen, N. D., and M. E. Mort. 2008. Determining patterns of genetic diversity and post-glacial recolonization of western Canada in the Iowa golden saxifrage, Chrysosplenium iowense (Saxifragaceae), using inter-simple sequence repeats. Biological Journal of the Linnean Society 95(4):815-823.
Nekola, J. C. 1990. Rare Iowa plant notes from the R. V. Drexler Herbarium. Journal of the Iowa Academy of Science 97(2):55-73.
Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis. 320 pp.
Packer, J. G. 1963. The taxonomy of some North American species of Chrysosplenium L., section alternifolia Franchet. Canadian Journal of Botany 41: 85-103.
Rosendahl, C. O. 1947. Studies in Chrysosplenium with special reference to the taxonomic status and distribution of C. iowense. Rhodora 49(578):25-36.