Jack-in-the-pulpit

Key ID characteristics:
  Jack-in-the-pulpit is most easily recognized by its distinctive flower from which it gets its name.  The "pulpit" is a cylindrical cone that has one flap which curls over the top and provides a protective cover for the "jack" inside.  The flower is only visible for a few weeks in the spring.
  If the flower is absent, you can also look for the berry cluster along with the three leaflet clusters.  The berry cluster starts out covered in a sheath, which wears away and exposes the unripe berries, which are green.  When the berries are ripen, they turn red.  I don't have any pictures of my own of the berries yet, but take a look at the links to get a view.
   There isn't any aboveground part of the stem, so the three leaflet clusters always grow directly from the ground and never branch off of a stem or trunk.  There can be one or two leaflet clusters per plant.
  The flower usually is not directly underneath the leaves, so you can see it from above.

Habitat:
Jack-in-the-pulpit is a common woodland wildflower that grows all across the eastern U.S. and Canada.

It can appear in clumps with multiple plants right near one another.  

Here is a picture of the plant as it is just emerging in the spring:

Here is a photo of a jack-in-the-pulpit in a sea of other spring woodland flowers (mostly trout lily):

All pictures in this post were taken at Nerstand Big Woods State Park in Nerstrand, MN.

Interesting tidbits:

The flowers are pollinated by fungus gnats (Sciaridae & Mycetophilidae) and the larvae of parasitic thrips.  They may emit a faint odor of stagnant water or fungi.

Mammals rarely eat the plant itself because it contains crystals of calcium oxalate, which makes it somewhat poisonous.  

"Jack" is the spathe in the middle of the flower, and contains both the male and female flower parts.  The "pulpit" is the spadix.

Links for further information:

USDA Plant Profile

Lady Bird Johnson Wildflower Center Native Plant Database

Zen's North Carolina Nature Notebook

all-creatures.org (lots of nice pictures here of the variation in flowers and fruits)

illinoiswildflowers.info