Marsh Marigold, or Perhaps Not?

I look forward each year to looking along streams to find one of my favorite spring wildflowers soon to be in bloom—Marsh Marigold (Caltha palustris). But it has an exotic cousin, a look-alike that threatens its existence and that of other native spring ephemerals such as Trout Lily (Erythronium americanum) and Spring Beauty (Claytonia virginica). It is Lesser Celandine (Ficaria verna).

Both Marsh Marigold and Lesser Celandine (also called Fig Buttercup, Pilewort, and Fig-crowfoot) are in the buttercup family, Ranunculaceae. They both have heart- or kidney-shaped leaves and yellow flowers.

So how do you tell them apart? Lesser Celandine’s leaves emerge really early in the spring, as early as February, and they are out now. When you are driving or hiking, look around to see what plants are in leaf. Many non-native invasives like Japanese Barberry (Berberis thunbergii) and Garlic Mustard (Alliaria petiolata) will leaf out before native plants, thereby outcompeting them for light. Check out stream and river banks and pond edges. Marsh Marigold is usually near the water’s edge. Lesser Celandine is more adaptable and can also be found in rich soils farther from water, even in sunny yards.

Lesser Celandine is a slightly smaller plant and flowers earlier than Marsh Marigold, usually in March or April here in Connecticut. If you see flowers on plants in late April to June, you can be almost certain it is Marsh Marigold. Marsh Marigold has 5 to 7 yellow tepals (undifferentiated petals or sepals), whereas Lesser Celandine has 7 to 11 yellow petals and 3 green sepals below the petals.

Invasive Lesser Celandine can form huge, extensive mats if left unchecked. The U.S. Department of Agriculture has predicted that it could establish itself in 79% of the continental United States. Now that’s an adaptable plant! It can do this because it forms tubers, which break off very easily through ground disturbance and flooding. After flowering, Lesser Celandine also forms bulbils in its leaf axils. This vegetative little bulb is a clone and can become a new plant.

How do you control this plant? If you have a small patch, try to eliminate it before it spreads into a monoculture. Control small patches by hand-digging the plant, making sure to sift out all tubers and throwing them in the trash. The tubers and roots are in the first 3 inches (about 8 centimeters) of the soil. Larger incursions are more difficult to control.

Marsh Marigold’s deep yellow flowers, larger than those of Lesser Celandine, are very striking near water. If you have a damp place in your yard in part to full sun, try growing it. It is sold at nurseries, particularly for plantings next to water or in rain gardens. Be sure to ask that the plants sold are nursery propagated.

Native plants like Marsh Marigold have spent thousands of years co-evolving with the pollinators in their ecosystem. Insects are co-evolved to feed on its leaves or gather its pollen and nectar. They in turn are fed on by birds. The nectar and pollen of the flowers of Marsh Marigold attract flies and bees, including the Giant Bee Fly (Bombylius major), syrphid flies, and halictid bees.

Yet, in a few decades, Marsh Marigold can be undone by non-native thugs like Lesser Celandine. By knowing the difference between the two and giving the native a chance to compete we can control the invasive and ensure a healthy ecosystem, even on a small scale like our own backyard or nearby streams.