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Wisconsin Plant of the Week

Impatiens pallida Nutt.

Balsaminaceae (Touch-me-not Family)

Common Name:

pale touch-me-not

09/11/2000

Impatiens is our only genus in this family and Wisconsin has two native species -- the orange spotted touch-me-not, I. capensis, and the yellow pale touch-me-not, I. pallida.  Until the flowers form,  plants from the two species are indistinguishable.

I. pallida is less common and grows in mesic woods and wooded floodplains usually on calcareous substrate. The plants are 1 to 2 m tall with succulent translucent stems with watery juice. The leaves are alternate, thin and ovate with coarsely toothed edges.  The flowers, which bloom from August until the first frost are up to 4 cm, and hang on long stalks from the axils of the leaves. The floral tube ends in a short spur (not visible in the photo).

The fruit is a capsule whose valves separate suddenly when the seed is ripe, throwing the seeds some distance from the plant. The common name refers to this explosive feature when touching the ripe capsules. The seeds also spread by floating on water.

Both Impatiens are true annuals whose seeds do not remain viable after one year. Since their propagation depends on at least some of the seeds being able to germinate, Impatiens have several ways to improve reproductive success under various conditions.

They have two types of flowers -- the flowers toward the top and outside branches open and are cross-fertilized by hummingbirds and insects; other flowers remain closed and are self-fertilized.  While seeds from these closed flowers lack the genetic diversity of cross-fertilization, they are easier for the plant to produce.

Impatiens are able to grow in a wide range of habitats due to both individual plants adapting to features in the environment and also by developing distinct ecotypes better adapted to certain conditions.  For example, regardless of the ecotype, plants in drier sites tend to be smaller to conserve moisture. But seeds of the “dry ecotype” produce plants with more closed flowers and set seed earlier than plants from the “wet ecotype” since selection favors early flowering where the plants are likely to be moisture stressed.  Differences among ecotypes here, as with all species, are not reflected in the Wetland Indicator Status.
 

  • Origin of the name: Impatiens, L., impatient; pallida, L. pallidus, pale
  • Range:  S. Canada, Nfld. to Sask., s. to OK, MO, NC, Mts in GA
  • WI Range:  Statewide except NW, often along large rivers
  • Common associates: Wood nettle, elms, maples
  • Wetland Indicator Status: FACW
  • Coefficient of Conservatism: C = 6 (S&W), C = 6 (MI)
  • ReferencesC.C. Bennington and J.B. McGraw. 1995. Natural selection and ecotypic differentiation in Impatiens pallida.  Ecological Monographs 65:303-323;
    G. Bell, M.J. Lechowicz, and D.J. Schoen. 1991.  The ecology and genetics of fitness in forest plants: III. Environmental variance in natural populations of Impatiens pallida, J. of Ecology 79:697-713.

     
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