Basis for Listing

Iodanthus pinnatifidus is a southern plant that ranges northward in the Mississippi River drainage to Minnesota. This species is exceedingly rare in Minnesota, where it prefers moist or wet alluvial woods along the Mississippi and Root rivers. When I. pinnatifidus was proposed as a state special concern species in 1984, there were only three historical records from Minnesota, dated 1886, 1902, and 1937. All were from hardwood forests in the southeastern corner of the state, but none had been relocated since their initial discovery. Since then, a comprehensive biological survey of the southeastern counties has been completed and just one population of this species was found.

It is likely that I. pinnatifidus has undergone a decline in numbers in the last century because of continued destruction and degradation of its floodplain forest habitat, especially along the Mississippi River. Beginning with the construction of locks and dams in the 1930s and continuing with the dredging of a navigational channel, the natural riverine habitats have rapidly disappeared. The riparian area of the Root River has also suffered extensive habitat changes. Many alluvial forests have been cleared for planting of row crops, and cattle are pastured where cultivation is impractical. Iodanthus pinnatifidus was subsequently listed as an endangered species in Minnesota in 1996.

  Description

Iodanthus pinnatifidus has stems up to 1 m (39 in.) tall, with thin leaves that are lanceolate to elliptic or oblong in shape with an acute or acuminate tip. The leaf margins are commonly sharply dentate or laciniate. Leaves taper to a petiole-like base, frequently with appendages around the stem. The larger or lower leaves are often pinnatifid at the base with 1-4 pairs of small segments. Racemes elongate before anthesis (flowering). Flowers are violet to nearly white. Fruits are slender, widely divergent, 2-4 cm (0.8-1.6 in.) long. Valves of the fruit are covered with minute, transparent, short, blunt projections (Gleason and Cronquist 1991).

  Habitat

Minnesota records of I. pinnatifidus are from floodplain forests (bottomlands) of the Mississippi and Root river valleys. These are seasonally flooded habitats typically dominated by Acer saccharinum (silver maple), Ulmus americana (American elm), and other deciduous trees.

  Biology / Life History

Iodanthus pinnatifidus is a perennial, insect-pollinated species. Specific pollinators and dispersal agents are unknown.

The best time to search for I. pinnatifidus is when it is in flower, from May to July.

  Conservation / Management

Land management should promote the protection and restoration of the vital floodplain forest habitat supporting this species. Land use changes that significantly alter its floodplain habitat could be detrimental to the species. The introduction and spread of non-native invasive plant species must be monitored closely, and controlled. The threat of displacement by invasive species is especially great from Rhamnus cathartica (common buckthorn), Alliaria petiolata (garlic mustard), and all of the non-native Lonicera spp. (Eurasian honeysuckle shrubs).

  Conservation Efforts in Minnesota

The Minnesota DNR County Biological Survey has been completed within the likely range of this species in the state, resulting in the discovery of one new population.

  References and Additional Information

Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. Second Edition. New York Botanical Garden, Bronx, New York. 910 pp.

Minnesota County Biological Survey. 1995. Natural communities and rare species of Goodhue County. Biological Report No. 44. Minnesota Department of Natural Resources, St. Paul, Minnesota.

Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis, Minnesota. 320 pp.