Rare Species Guide

  Basis for Listing

Iodanthus pinnatifidus (purple rocket) 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 tributary rivers (Paleozoic Plateau Section). 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. In 1988, a DNR botanist discovered a small population on a state Scientific and Natural Area and since then, two new occurrences of this species have been confirmed.

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 tributary rivers have also suffered extensive habitat changes. Many alluvial forests have been cleared for planting of row crops, and cattle are often 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) and can become quite long. Flowers are violet to nearly white. Fruits are slender, widely divergent, and 2-4 cm (0.8-1.6 in.) long. Valves of the fruit are covered with short blunt transparent projections (Gleason and Cronquist 1991).

  Habitat

Minnesota records of I. pinnatifidus are from floodplain forests (bottomlands) of the Mississippi, Cannon 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 an insect-pollinated perennial species. Specific pollinators and dispersal agents are unknown, but it is said to attract bees and butterflies. The seeds are small and possess no morphological structures indicative of a specialized dispersal mechanism. It is likely they are dispersed short distances by small ground foraging animals and perhaps longer distances by spring floodwaters.

  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).

  Best Time to Search

The best time to search for Iodanthus pinnatifidus is when it is in flower, from early June to mid-July.

  Authors/Revisions

Welby R. Smith (MNDNR), 2021

(Note: all content ©MNDNR)

  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. Minnesota County Biological Survey Biological Report No. 44. Minnesota Department of Natural Resources, St. Paul.

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