The flower is 3 to 4 inches tall and about 2 inches across, made up of a 2 to 3 inch long club (the “Jack”, or spadix) sitting in a tubular base with a hood (the “pulpit”, or spathe). The spadix is light green to reddish green. The spathe is light green to purplish green and often dotted with white or purplish stripes. Plants are either male or female and the flowering structure looks essentially the same from the outside, with the staminate or pistillate flowers hidden on the lower part of the spadix at the bottom of the tube.
Leaves emerge after the flowers, in 1 or 2 sets of compound leaves (male and non-flowering plants have 1, female 2), each leaf with 3 leaflets. Each leaflet is up to 7 inches long and 3 inches across, generally oval with a pointed tip. The middle leaflet is generally larger than the lateral 2. The leaves can tower over the flower and hide it from view.
The vein pattern is distinct with a continuous vein around the edge of the leaf, creating a border effect. The leaf edges are a bit wavy but otherwise smooth. Stems are smooth and green to purple, or mottled green and purple.
While Jack-in-the-pulpit has both male and female plants, they can change gender from year to year, apparently in response to successful (or failed) reproduction the previous year. Males resprout from an underground corm that can last several seasons, the corm sending off shoots and producing new plants as well. Males tend to be smaller than females and have a small hole at the bottom of the spathe which allows pollinators to escape (with their pollen) more easily. Female plants lack the hole and pollinators are more likely to become trapped, better ensuring successful pollination. Sneaky devils. Jack-in-the-pulpit leaves might be confused for a species of Trillium, but Trillium leaves tend to be proportionately broader and the vein pattern lacks the border effect of Jacks.