Leavenworthia Compared to Hairy Bittercress

I’ve recently received emails from two different people, describing their exciting discoveries of populations of the state threatened Leavenworthia uniflora in their lawns and flowerbeds. It’s always exciting to find a population of rare plants, especially when they’re growing as thick as weeds, which is how one correspondent described his find. They had both read some of my earlier posts on the species and wanted me to share in their joy of their newfound flora neighbors.

Unfortunately, the photo documentation they sent along with their emails showed the plants to be something other than Leavenworthia.  Their plants did bear a superficial resemblance to the Leavenworthia, but they were actually a non-native weedy species known as Hairy Bittercress, Cardamine hirsuta. No wonder they were thick as weeds.  I thought it appropriate to make a comparison between the two plants using easy to see features. I certainly don’t want people to be protecting weeds because of a mistaken identification, nor would I want a rare plant to be destroyed because of the same mistake.

Leavenworthia will grow in most locations that provide competition free conditions. In natural situations these are generally dry, rocky, shallow soils. These are annual plants that begin growth in early winter and by early spring, begin to flower. Leavenworthia produces leaves from a basal whorl. The leaves fan out horizontally, almost hugging the ground and presenting an appearance of level flatness across the top of the plant.

Hairy Bittercress has a growth habit similar to that of Leavenworthia, but is more typically found in areas of urban disturbance such as is found in people’s yards. It also begins growth in early winter, but it tends to flower one or two weeks earlier than Leavenworthia. The plant begins by producing several rings of basal leaves, but as it grows, the center portion of the whorl heaves upward, making the plant appear slightly mounded.

Leavenworthia flowers emerge from ground level at the center of the leaf whorl.  Flower stalks produce no leaves and bear only a single bloom at the top of the stalk.

Hairy Bittercress produces a branched stalk from the center of the whorl that produces both leaves and clusters of flowers.

Hairy Bittercress, shown on the left, produces compound leaves with leaflets that produce rounded lobes. The Leavenworthia develops sharply pointed lobes.

Here we have Leavenworthia on the left and Hairy Bittercress on the right. Hairy Bittercress most resembles Leavenworthia in its younger stages. I have yet to see both of these species actually growing together in a single location. To get this photo, I plucked a Hairy Bittercress rosette from another location and posed it beside the Leavenworthia. It’s easy enough now when making plant identifications to go online and find authoritative information about the plant in question. When doing that type of search, just make sure you go beyond the photo and read what the text has to say about the plant.