Basis for Listing

The status of Trillium nivale is somewhat equivocal. Although it grows in fifteen states and is considered "secure" nationwide, populations are considered "scattered to rare across its range" (NatureServe 2009). The species is listed as endangered or threatened in half of the states in which it occurs, and it is watch-listed or special concern in the remainder of states. First documented as "local and rare" in Minnesota in the late 19th century (MacMillan 1892), Minnesota's T. nivale populations vary wildly in size, with many of the largest located in vulnerable areas. The horticultural popularity of this species among wildflower gardeners is no assurance of its perpetuation, and actually places natural populations, in states where it is not protected, at greater risk. Given its rarity and vulnerability, T. nivale was listed as a special concern species in Minnesota in 1984.

  Description

Trillium nivale is a small plant, up to 10 cm (4 in.) tall. Its flowers are erect, facing up above the whorl of leaves. Petals are white, up to 3.5 cm (1.4 in.) long, and up to 1.5 cm (0.6 in.) wide (Case 2002). Both the sepals and leaves have a slight bluish-green cast. Trillium nivale can be distinguished from all other Minnesota trilliums not only by its earlier flowering period, but also by its whorl of 3 small, oval leaves with prominent parallel veins. Also unlike other members of the genus in Minnesota, the tips of the leaves in T. nivale are rounded. Leaves can be up to 4.5 cm (1.8 in.) long and 3.4 cm (1.3 in.) wide. Immature plants may exhibit 1 or 2 leaves (Martin 1935), which are recognizable by their shape, color, and vein pattern similar to flowering plants.

  Habitat

Most plant communities in which T. nivale occurs are classified as mesic hardwood forests dominated by Acer saccharum (sugar maple), Tilia americana (basswood), and Quercus spp. (oaks). Among canopy oaks, Q. rubra (northern red oak) prevails in the Paleozoic Plateau and only Q. macrocarpa (bur oak) is present in the drainages of the Cottonwood and Des Moines rivers. Populations along the Cottonwood River extend onto riparian terraces where the canopy has been lost due to Dutch Elm disease. The number of associated spring ephemerals declines from southeast to west and northwest. Sanguinaria canadensis (bloodroot) and Allium tricoccum (wild leek) most consistently co-occur with T. nivale throughout its Minnesota range. Similar spring groundlayer associates are found in slope and floodplain terrace habitat, but floodplain terraces tend to be dominated by Laportea canadensis (wood nettle) later in the summer.

As is the case throughout its range, Minnesota's populations of T. nivale prefer fine, moist, calcareous soils in previously glaciated areas. More Minnesota populations are located on prairie soils than on forest soils, but in the most extreme southwesterly cases, microhabitats may be influenced by groundwater discharge. All but two populations in the state lie within 183 m (600 ft.) of a stream. All populations in the Blufflands subsection of the Paleozoic Plateau are situated adjacent to designated trout streams. Despite their proximity to streams, the majority of Minnesota T. nivale populations occur on loamy soils on fairly steep slopes. In the prairie region of the state, five populations attain large size in floodplain forests and open floodplains on alluvial soils. Although the species was first documented in the southeastern part of the state, only one population in the Paleozoic Plateau is comparable in size to the large populations found in the Minnesota River Prairie and Coteau Moraines subsections. The state's largest populations are concentrated in the lower reaches and tributaries of the LeSueur and Blue Earth rivers, the Minnesota River Valley near Mankato, and the upper Cottonwood River in Lyon County. Populations in the Hardwood Hills subsection are located on rolling moraine between small lakes.

  Biology / Life History

Trillium nivale is a perennial spring ephemeral; one of a group of plants that emerge, photosynthesize, flower, and set seed during the brief time when leaves of forest canopy trees have not fully developed. The species thus experiences sunny or partially shaded conditions at the time it is above ground, but later in the summer, the habitat may be heavily shaded. Although March flowering is reported in states east of the Mississippi River, Minnesota populations of T. nivale tend to flower from early April through mid-May. Individual plants are reported to reach sexual maturity at three and to live to at least eight years of age (Nesom and La Duke 1985). The longevity of populations is not known, but one Minnesota population was first observed in 1908.

Although T. nivale colonies are often highly aggregated, producing an appearance of "drifts" of blossoms in the woods just as the snow is melting, clonal development is reported to be relatively unimportant (Nesom and La Duke 1985). The pollinator appears to be unknown. Fruits in Minnesota populations develop from mid-April through late May. After fertilization, the peduncle (stem of the flower) turns downward so that by the time the fruit is mature it is hanging below the leaves (Martin 1935; Nesom and La Duke 1985). Trillium nivale is one of a group of spring ephemerals whose seeds are dispersed by ants after the mature fruits have fallen on the forest floor (Smith et al. 1989). The dependence of the species on ant dispersal may account for the low genetic diversity reported among and between Ohio populations (Bayer et al. 1987). Recruitment of young plants can be very high in some Minnesota populations, with ratios of ten or more single-leaved, first year plants to each flowering plant recorded in at least one population.

  Conservation / Management

Minnesota is one of the strongholds for T. nivale, but many of the largest populations occur in places where they are subject to rapidly expanding residential development and/or increased recreational use. Although only one population is in the Twin Cities Metropolitan Area, eight of the state's populations are in the rapidly expanding development perimeter of Mankato. Several more are wholly within the city limits of Jackson. In all these cases, development, intensive land use, direct conversion to lawns and recreational uses, and potential expansion of Rhamnus carthartica (common buckthorn) and Alliaria petiolata (garlic mustard) are potential threats. The impact of canopy loss is not known, but may vary between harvested slope forests and floodplains where Ulmus spp. (elms) have died but other tall vegetation shades the ground during the summer months. The potential impact of large white-tailed deer (Odocoileus virginianus) populations, trail erosion, and exotic earthworms is unknown, but all three factors are known to be present at some T. nivale sites. The potential threat of competition from R. cathartica and A. petiolata is increasingly likely.

  Conservation Efforts in Minnesota

Very few T. nivale populations occur in sites where protection of rare features is the primary land management goal. The three populations that occur in state Scientific and Natural Areas or private preserves are among the state's smallest. Three populations occur in county and local parks, one of which supports the largest overall population in the state. At the present time, no special management on behalf of the species is known to occur at any of these sites. Potential threats from Alliaria petiolata and erosion are greatest in areas where trails pass through T. nivale populations.

  References and Additional Information

Bayer, R. J., J. C. La Duke, and D. J. Crawford. 1987. Isozyme variation in Trillium nivale (Liliaceae). Canadian Journal of Botany 65:2250-2254.

Case, F. W. Jr. 2002. Trillium. Pages 90-117 in Flora of North America Editorial Committee, editors. Flora of North America North of Mexico. Volume 26. Oxford University Press, New York, New York.

MacMillan, C. 1892. The metaspermae of the Minnesota Valley: A list of the higher seed-producing plants indigenous to the drainage-basin of the Minnesota River. Harrison and Smith, State Printers, Minneapolis, Minnesota.

Martin, J. N. 1935. The distribution and life history of the Trillium nivale Riddell. Proceedings of the Iowa Academy of Science 42:49-54.

NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. . Accessed 30 March 2009.

Nesom, G. L., and J. C. La Duke. 1985. Biology of Trillium nivale (Liliaceae). Canadian Journal of Botany 63:7-14.

Smith, B. H., P. D. Forman, and A. E. Boyd. 1989. Spatial patterns of seed dispersal and predation of two myrmecochorous forest herbs. Ecology 70(06):1649-1656.