Chrysosplenium iowense Rydb.
Iowa Golden Saxifrage
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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 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 persisted in isolated pockets of habitat where cold microhabitat remained essentially unchanged. Because of the generally temperate climate of Minnesota and Iowa, the plants are 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.
Although C. iowense is an inconspicuous plant in its native habitat, it is technically quite distinct from any other species with which it might occur. Though very short, the stem is erect and glabrous, producing thin stolons. Leaves are alternate, and lower leaves are roundish with 7-11 lobes and nearly closed sinuses. The upper 2 leaves are basally adnate to branches in the inflorescence. Flowers are yellowish green with yellow anthers. Plants often occur in moderately dense, though often small, patches. The only other member of this genus in Minnesota is C. americanum (American golden saxifrage), which does not occur in the same habitat as C. iowense and differs from it in having a decumbent stem with opposite leaves.
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 1 m² (10.8 ft.²). 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 (dwarf alder), 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 classification of the alternate-leaved Chrysosplenium is a confusing and hotly debated issue. For example, several botanists consider C. iowense to be endemic to Minnesota and Iowa and distinct from the Canadian plants, which they refer to as C. tetandra (northern golden saxifrage). There are also authorities who consider both C. iowense and C. tetandra to be varieties of the European C. alternifolia (alternate-leaf golden saxifrage). The position adopted here is derived from Rosendahl (1947) and Packer (1963). They consider the Midwestern plants to be conspecific with the plants of western Canada (C. iowense) but distinct from the arctic plants (C. tetandra) and the European plants (C. alternifolia).
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 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 yd.²) 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 (especially logging 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.
Conservation Efforts in Minnesota
Nekola, J. C. 1990. Rare Iowa plant notes from the R. V. Drexler Herbarium. Journal of the Iowa Academy of Sciences 97(1):55-73.
Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis, Minnesota. 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):25-35.