invasive plants

All posts tagged invasive plants

By Ian Stewart, Ashland Nature Center Weekend Naturalist

Anyone walking the creekside trails at Ashland Nature Center in early spring is likely to see three very different and distinctive yellow flowers. At first glance these bright flowers are a welcome sight after the long hard snowy winter. Look more closely however and they are not so welcome – all three are alien invaders native to Europe which have now become firmly established in the US.

The most abundant of these species, and the one that has the most negative effects upon native wildflowers, is the Lesser Celandine (Ranunculus ficaria). This is in the buttercup family and is commonly found in damp areas like floodplains where it forms dense green carpets studded with shiny yellow flowers. It is particularly problematic because the heart-shaped leaves appear early and are packed so tightly together that the later-emerging native flowers never receive enough sunlight to fully develop.

Lesser Celandine blooms over a dense carpet of their foliage.

Lesser Celandine blooms over a dense carpet of their foliage.

Once established, Lesser Celandine can smother just about all other plants, especially on floodplains.

Once established, Lesser Celandine can smother just about all other plants, especially on floodplains.

The second is the Dandelion (Taraxacum officinale), a flower in the Aster family that is a perennial source of frustration to anyone who tries to maintain a tidy lawn. It gets its peculiar name from its long toothed leaves which were thought to resemble lion’s teeth (or ‘dent de lion’ in French, which over time became corrupted to ‘Dandelion’). The yellow flower heads later become gray spherical ‘clocks’ of seed which are easily dispersed by even a light breeze or human touch, so it is not hard to see how they have become so widespread.

The ever-familiar lawn weed...Dandelion.

The ever-familiar lawn weed…Dandelion.

The third not-so-mellow yellow is the Daffodil (Narcissus sp.). Daffodils do not occur in carpets like the Celandine or in loose clusters like the Dandelion but regrow in the same place each year, as the bulbs contain toxic substances and few animals eat them. Daffodils and Dandelions are both tolerant of a wide range of soil conditions and can be found growing throughout the state.

Daffodils can be found growing throughout Delaware, but especially near places near human settlements.  They pop up in the strangest places far from humans too, but are not native.

Daffodils can be found growing throughout Delaware, but especially near places near human settlements. They pop up in the strangest places far from humans too, but are not native.  Lesser Celandine meets Daffodil.  Daffodil wins.

Invasive flowers such as these three species present many problems for native flora and fauna. As well as simply blocking out sunlight and using up soil nutrients they likely host fewer native arthropods which in turn reduces the amount of food available for animals higher up in the food chain such as small mammals and birds. Plus, they seem less likely to be eaten by native animals, perhaps because they have not evolved with them, which is probably part of the reason they have become so widespread. They were probably introduced by European settlers for obscure medicinal purposes and as colorful reminders of their homeland gardens, but whatever the reason, we are stuck with them now. However, there are many native alternatives if you would like to plant early spring flowers, including Trillium (Trillium sp.), Bloodroot (Sanguinaria canadensis) and Spring Beauties (Claytonia sp.), and Common Blue Violets (Viola sororia). All of these produce attractive, colorful flowers that would enhance any garden!

Ian Stewart

Weekend Naturalist