By Tom Schweich
A reader wrote to Barb concerned that a recent composite photo in this column showing wildflowers on Schweich Hill included a very pretty, but pernicious and state-listed Noxious weed. Here are five common plants with pretty flowers, that are also very invasive weeds.
Dalmatian toadflax – Linaria dalmatica L.
Dalmatian toadflax has a bright yellow snapdragon-like flower with a long spur on the back side. It is a Colorado-listed Noxious Weed and is found in all Golden parks and open spaces. It is hard to eradicate because it spreads rapidly by seeds and by underground stems called rhizomes.
There is also less common and smaller Linaria vulgaris L. commonly called butter and eggs, though I see it more in the high country. The two Linaria also hybridize, producing an intermediate plant.
There is also a native toadflax in Golden – Linaria texana Scheele – but the flowers are blue making it easy to distinguish from Dalmatian toadflax and butter and eggs.
Hairy Willowherb – Epilobium hirsutum L
Hairy willowherb (Epilobium hirsutum) is a perennial, semi-aquatic plant also known by the names “codlins and cream” and “European fireweed.” The plant grows up to 6 feet tall and can reproduce via seeds or rhizomes. The entire plant is covered with fine, soft hairs, hence the name hairy willowherb.
Infestations can clog small waterways and displace native vegetation, increasing bank erosion and degrading wildlife habitat.
Hairy willowherb is a newcomer to Colorado, found for the first time at the Ward Road Ponds near Mount Olivet Cemetery in 2003. Since then, it has spread to numerous places in Golden on both private and public land.
We also have native willowherbs in and around Golden. Hairy willowherb is often found growing with them and eradication efforts require a careful identification to avoid eradicating the native plants.
Hounds Tongue, Gypsyflower – Cynoglossum officinale L.
Cynoglossum officinale L. “Gypsyflower” or “Hounds-tongue” has been found in almost every Golden open space and in many parks.
It was first seen in Jefferson County in 1961, about 1 mile east of Golden.
The common name of hounds-tongue is a translation of the Greek words in its scientific name Cynoglossum, "kynos" (κύων) meaning dog, and "glossa" (γλῶσσα) meaning tongue. The name refers to the shape and texture of the plant's leaves, which some have likened to a dog's tongue.
The seeds of hounds-tongue are covered by little hooks, and they will attach themselves to your shoes and pants, hitching a ride wherever you go.
Saponaria officinalis L. Bouncingbet
Around Golden, I see this plant primarily as a landscaping plant. I also notice that the white-lined sphinx moth (
Hyles lineata) is really attracted to the nectar of this plant in the evenings.
Bouncingbet is listed as a Noxious weed due to its toxicity to livestock and humans, its ability to displace native vegetation, and its potential to spread through seeds and rhizomes. It is also considered a nuisance weed due to its invasive nature in disturbed areas
Hesperis matronalis L. “Dame’s Rocket”
Dame’s rocket has been a cultivated species for a long time.
The successful spread of dame's rocket in North America is attributed to its prolific seed production and because the seeds are often included in prepackaged "wildflower seed" mixes sold for "naturalizing."
Dame's rocket poses ecological problems by outcompeting native plants, forming dense monocultures, and potentially acting as a host for viruses harmful to crops. It spreads to woodlands, prairies, and disturbed areas from a garden.
In Colorado, dame’s rocket is a List B Noxious Weed. In Golden it has been found at Heritage Dells, in Kinney Run, along the Welch Ditch, and at DeLong Park.
And … more that are not listed above …
There are many more plants that can be pretty and pernicious. Some of them not listed above are:
Myrtle Spurge – Euphorbia myrsinites L., was sold as an ornamental until recently, the sap is dangerous to humans and animals.
Leafy Spurge – Euphorbia esula L., not quite as dangerous as the above, but very invasive.
Thistles – Cirsium sp., etc. We have many non-native thistles invading our parks and open spaces but be careful when pulling out thistles, we do have one native thistle.
Mulleins – Verbascum sp., most everyone recognizes the common mullein – Verbascum thapsus L. – but we also have two less-common mulleins in Golden: V. blattaria and V. phlomoides. V. thapsus and V. blattaria are state-listed Noxious weeds.
Sweet Clovers – yellow sweet clover (Melilotus officinalis (L.) Lam.) and white sweet clover (M. alba Medik) are invading our parks. Honeybees really like them for their nectar. They are not listed noxious weeds, though they are in several other states.
Finally, we have two very valuable agricultural plants,
alfalfa (Medicago sativa L.) and smooth brome (Bromus inermis Leyss.), that are taking over large areas of our parks and open spaces.
