Colorado Mountain Gardener: Noxious weed look alikes

by Irene Shonle

It is heartening to see so many people being committed stewards of their land who are working to eradicate the noxious weeds on their property. Thank you to everyone who is participating! A word of caution - it is possible to be a little too enthusiastic. This happens when someone pulls or treats the wrong plant – a plant that has the misfortune of looking like a noxious weed. These look-alike plants are often native, and can provide good habitat for pollinators, or at the very least, will occupy space that otherwise could be invaded by a noxious weed, so it’s best to learn how to distinguish which is which.

Some of the most common mistaken identities up here are:

Golden banner/yellow toadflax,
Pineapple weed/scentless chamomile,
Cutleaf daisy/oxeye daisy
Fireweed/purple loosestrife.

Golden banner is a native plant – it blooms in the spring, and has solid yellow flowers, and three-lobed (trifoliate) leaves. Yellow toadflax blooms in the second half of summer with two-tone yellow flowers with a darker throat, and has strap-shaped leaves.

Golden banner

Yellow toadflax

Pineapple weed, while an introduced plant, is not on the noxious weed list. It is, however, having a very good year, and can be easily controlled by hoeing or pulling. It has ferny leaves that, when crushed, smell like pineapple. The whole plant only gets to 6-8” tall at the most. It develops small yellow buttons, but never white ‘petals’ (ray flowers). Scentless chamomile also has ferny leaves, but they have no odor (the plant names give good ID clues). It gets up to 3’ tall, and has hundreds of white flowers.

Pineapple weed

Scentless chamomile

Cutleaf daisy is a native plant with small white flowers and finely cut leaves that could look a little ferny. It can (and has been) mistaken for pineapple weed, scentless chamomile and oxeye daisy. The flowers on the native bloom in the spring, and the foliage has no smell. The whole plant is no taller than about 4” tall. Oxeye daisy blooms mid-summer, and has much larger flowers, as well as broader leaves with teeth (not ferny). The plant grows 1’-3’ tall.

Cut-leaf daisy and penstemon

Oxeye daisy

Fireweed is a native plant with 4 pink petals. It blooms mid-summer to fall. The leaves are alternate, and the plant can grow up to 4’ tall. Purple loosestrife is not known to be up at this elevation, but people have frequently pulled out fireweed by mistake. Loosestrife has opposite leaves (or even whorled – meaning that four leaves come out of the stalk at the same place). It has 5-7 purple petals and can grow up to 8’ tall.

Fireweed

Loosestrife

Finally, we have many wonderful native thistles, and it’s easier to just learn to recognize our two common noxious thistles, Canada thistle and musk thistle, rather than all of the native thistles. Musk thistle has large, solitary purple flowers with a formidable row of teeth under the flower. The leaves have a whitish edge. Canada thistle usually forms thickets due to the root system, and has clusters of small purple flowers. See below table for a quick reference to distinguishing these plants.

Native plant	Bloom	Leaves	Noxious weed	Bloom	Leaves
Golden Banner	Solid yellow, spring	Three-parted	Yellow toadflax	Two-toned with a darker throat, Mid-late summer	Strap-shaped
(Pineapple weed – not native, but not noxious)	Just a yellow button, spring-mid summer	Ferny, smells of pineapple	Scentless chamomile	White flowers, Mid-late summer	Ferny, odorless
Cutleaf daisy	Small white flower, spring	Finely cut, a little ferny	Oxeye daisy	Large, white, blooms	Small teeth on leaves
Fireweed	4-petals, pink, mid-late summer	Alternate leaves	Purple loosestrife	5-7 pink petals, mid-late summer	Square stem, 4 or more leaves come out of same place on stalk (whorled)
Native thistles	Varies – white, pink, brownish	Varies – usually very white on underside	Noxious thistles (especially Canada and Musk)	Purple-pink	Varies