The ground is thawing out and the skunk cabbage is up – it’s time to start searching for the purple rock cress (Cardamine douglassii), a state-threatened plant. You may also find its more common cousins, all members of the mustard family – yes, like the mustard you eat, but with white to pink flowers rather than yellow. Moist woodlands with oak, hickory, and maple are a good place to look, including forests with vernal (spring) pools. Perhaps you might be out looking for frogs and salamanders around this time of year, if so -keep an eye out for these early flowering plants, too. Woodland rock cresses tend to be small, only about 3 to 8 inches tall, so they are easy to miss. If you see some patches of green that are not mosses or mounds of sedges (grass-like plants), take a closer look – you may be rewarded with some delicate flowers.
Forests with vernal pools or small streams or wetlands are a good place to look for these cresses.
Look for patches of green on the forest floor and take a closer look. You might find some flowers.
A close-up of that woodland patch of green reveals this beautiful plant, the cut-leaved rock cress or cut-leaved toothwort (Cardamine concatenata), a common woodland wildflower. This used to go by the name Cardamine laciniata or Dentaria laciniata. It is easy to identify by its lacy leaves that look a bit like bird tracks.
Several of the other rock cresses, including the purple rock cress, have smaller and less complex leaves like this or just small roundish leaves on the stem or at the base of the plant (see in background).
Spring cress (Cardamine bulbosa) is another common cress that blooms very early. The flowers can range from white to pink, and it can be hard to tell this apart from the rare purple rock cress. Note that all of the flowers in the mustard family have 4 petals regardless of their color.
Here is the rare Cardamine douglassii, so similar to the spring cress above. One has to consult the botanical keys in order to figure out which species you have. Some trout lilies are coming up too (leaves at upper left).
NY Natural Heritage and State Parks staff discovered two new locations for this rare species in State Parks in the past few years and hope that more are found in this year’s early spring surveys.
The flowers of the cresses don’t last long, only until the trees leaf out. Once in fruit, you can still recognize them by their elongate seed pods, which give rise to yet another common name for this group of plants, the “rockets”.
Post written by Julie Lundgren, NY Natural Heritage Program
NY Natural Heritage Program is affiliated with SUNY College of Environmental Science and Forestry (SUNY ESF) and works in close partnership with NYS Parks and NYS DEC. NYNHP conducts many kinds of surveys and studies to provide guidance and tools for conservation of native biodiversity across New York State.
Recommended references for identifying the rock cresses:
Newcomb’s Wildflower Guide by Lawrence Newcomb. Little, Brown and Co. 1989.
For more information:
NY Flora Atlas Purple Rock Cress
NYNHP Conservation Guides Purple Rock Cress