Luzula parviflora (Ehrh.) Desv.
Click to enlarge
Luzula parviflora ssp. melanocarpa, Luzula parviflora var. melanocarpa
Basis for Listing
In Minnesota, Luzula parviflora (small-flowered woodrush) is restricted to the Arrowhead region in the northeastern corner of the state (Northern Superior Uplands). This is an area with large tracts of forest, where suitable habitats for this species appear to be wide-spread. Yet extensive searching has found only a relatively few small isolated colonies. It is unclear why this species is so rare and why so few individuals exist at each site, but it is likely related to the biology of the species, rather than historical factors. Threats are largely related to timber management, especially clear-cutting and site preparation. However, threats from residential and recreational development are increasing in this part of the state as well.
When L. parviflora was first proposed for protective status in Minnesota in 1984, it had been recorded only three times in the state and all were pre-1948 (Coffin and Pfannmuller 1988). It was not listed at that time due to lack of current information. Subsequently, more information became available, and it was cautiously listed as special concern in 1996. A more protective status was considered at that time, but it was thought more field work was needed to clarify its status. After several years of targeted field inventories by the Minnesota Biological Survey, its rarity has been confirmed and additional threats have been revealed. For these reasons, its status was elevated to threatened in 2013.
Luzula parviflora can be a relatively tall plant, sometimes reaching 80 cm (2.6 ft.) in height. However, the stems and inflorescence are rather sparse, which can make the plant difficult to spot in some situations. The inflorescence is a loose compound cyme, with small flowers occurring singly at the tips of the branches. Each flower develops into a shiny dark capsule containing 3 seeds. The basal leaves are flat and relatively wide, sometimes as wide as 1.5 cm (0.6 in.). The stem leaves are smaller and narrower than the basal leaves. Many plants in a population exist as sterile rosettes of basal leaves without any stem.
There are three species of Luzula native to Minnesota and all are recognizable by having long hairs on the leaves, a feature not seen in most grasses or sedges. Of the three Luzula, only in L. parviflora are the flowers solitary at the ends of branches in a compound inflorescence. The inflorescence of L. acuminata (pointed woodrush) is simple rather than compound, meaning it branches only once, and the inflorescence of L. multiflora (many-flowered woodrush) is composed of tightly packed flower clusters.
In Minnesota, L. parviflora is associated with a variety of forest types, including dryer portions of conifer swamps with Thuja occidentalis (northern white cedar) or Picea mariana (black spruce); variously wet hardwood forests with Fraxinus nigra (black ash); and upland forests with a variety of hardwoods or conifers. Within these larger forest types, L. parviflora typically seeks out areas where conditions grade from an upland to a lowland or from mesic soil to wet soil. Although L. parviflora is not truly a swamp species, it can be found on slightly elevated microhabitats within a swamp, where its roots can be in well-aerated mosses or poorly decomposed organic material rather than in saturated peat.
Biology / Life History
Luzula parviflora is a short-lived perennial adapted to shaded and acidic forest environments. It appears that the flowers are wind-pollinated, and the seeds are gravity and/or insect dispersed. It produces horizontal off-shoots in the duff layer, however, normally only one is produced each year, so the plant does not form dense clumps of stems. These off-shoots typically produce sterile rosettes the first year, which may produce flowering culms in subsequent years. Often these basal rosettes outnumber the flowering plants, frequently by a large margin. The leaves of the basal rosettes resemble those of the flowering culms and can be easily recognized.
Conservation / Management
The only immediate management consideration is the maintenance of important habitat parameters where colonies of L. parviflora occur. This entails preserving the structure of the canopy trees and the integrity of the soil environment. Natural processes can be relied upon to achieve these goals even though storms, insect outbreaks, and wildfire do occur in the region and might appear to damage the forest habitat. In fact, these stochastic and cyclical events are components of important ecosystem processes that maintain the habitat on the large scale by regenerating it on the small scale. Human activities, such as mining, road and trail building, lakeshore development, and to some extent logging are different than these natural processes and tend to have a harmful effect on habitats of L. parviflora.
Best Time to Search
The best time to search for L. parviflora is when the reproductive structures are mature, from early July through August.
Conservation Efforts in Minnesota
Many of the known colonies of L. parviflora in Minnesota occur on public land in the Superior National Forest. This presumably protects the habitat from most types of development but not from logging, mining, road building, or recreational activities.
Welby Smith, MN DNR, 1988, 2008, and 2018
Cheney, L. S. 1893. A contribution to the flora of the Lake Superior Region. Transactions of the Wisconsin Academy of Sciences, Arts and Letters 9:234-254.
Lakela, O. 1965. A flora of northeastern Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 541 pp.
Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.
Penskar, M. R., and S. R. Crispin. 2008. Special plant abstract for Luzula parviflora (small-flowered woodrush). Michigan Natural Features Inventory, Lansing, Michigan.
Shackleford, R. 2003. Conservation assessment for Small-flowered Woodrush (Luzula parviflora (Ehrh.) Desv.). United States Forest Service, Eastern Region, Milwaukee, Wisconsin.
Swab, J. C. 2000. Luzula. Pages 255-267 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 22. Oxford University Press, New York, New York.