Conyza canadensis (Horseweed)

Conyza canadensis (L.) Cronquist

Horseweed, Canada horseweed

Kingdom	Plantae	Plants, but not fungi, lichens, or algae
Subkingdom	Tracheobionta	Vascular plants—plants with a “circulatory system” for delivering water and nutrients
Division	Magnoliophyta	Flowering plants, also known as angiosperms
Class	Magnoliopsida	Dicotyledons—plants with two initial seed leaves
Subclass	Asteridae	A large class that encompasses asters
Order	Asterales	Flowering plants with a central disk flower and surrounding petals, like daisies
Family	Asteraceae	The aster family, which also includes daisies and sunflowers; from the Greek ἀστήρ, “star,” for the star-shaped flowers
Genus	Conyza	From Greek konops, “flea,” for the use of the leaves in beds as a flea repellant
Species	canadensis	“From Canada”

About plant names...

Horseweed is a native weed that is widespread in North America, now also found in Europe, Asia, Africa, and South America. It is a serious problem in some regions, competing actively with crops.

Identification: Plants are 20-79" (50-200 cm) in height, with a single erect stem that has bristly hairs on it. Leaves grow alternately from the stem in a pattern that looks whorled, but isn’t. They are all about the same length and orientation, making the plant resemble a green cylinder. Leaves are narrowly lanceolate or oblanceolate, 3-4" (7.6-10 cm) × ½" (1.3 cm). They are mostly untoothed, but have a few teeth toward their tips, and they have small white hairs along their edges. The top of the plant branches into a shape like the top of an ice cream cone, which becomes covered with a profusion of little flowers. The flowers are greenish-white, but only ⅛" (3.2 mm) in size. They are composite flowers, producing tiny white ray flowers as well as itsy-bitsy yellow disk flowers, but their small size and coloring overall is barely noticeable. Flowers appear from June to October. Although horseweed is big and common, you are likely to overlook it completely unless it starts muscling out your vegetables—it just isn’t a showy plant.

Edibility: Young leaves and seedlings are edible when cooked. Dried leaves have a flavor said to be similar to that of tarragon. An oil extracted from the leaves is used as a flavoring agent.

Medical: Plants produce dermatitis in some people. The common name sneezeweed derives from its use as a snuff to induce sneezing in herbal medicine, in hopes of lessening cold symptoms. Its smoke has been used as an insect repellant. Like many common plants, it has a host of other purported medical uses, among them treatment of gastrointestinal problems, rheumatism, dysentery, internal haemorrhages, gonorrhoea, and menstrual problems.

Online References:

Conyza canadensis at Illinois Wildflowers

Conyza canadensis on www.eattheweeds.com

Conyza canadensis on Plants for a Future, a resource and information centre for edible and otherwise useful plants

Conyza canadensis on CalPhotos

Conyza canadensis at Minnesota Wildflowers

Conyza canadensis on luirig.altervista.org

Conyza canadensis on biology.burke.washington.edu

Conyza canadensis on eFloras

7/31/2012 · Bemis Rd Conservation Area, Pepperell, Massachusetts
≈ 14 × 19" (34 × 48 cm) ID is uncertain

8/2/2012 · Nashua River Rail Trail, near Nashoba Hospital, Ayer, Massachusetts
≈ 6 × 9" (14 × 22 cm)

8/20/2012 · Nashua River Rail Trail, Groton Center, Groton, Massachusetts
≈ 3½ × 5" (9.2 × 13 cm)

8/2/2012 · Nashua River Rail Trail, near Nashoba Hospital, Ayer, Massachusetts
≈ 5 × 8" (13 × 19 cm)

8/20/2012 · Nashua River Rail Trail, Groton Center, Groton, Massachusetts
≈ 6 × 9" (15 × 23 cm)

8/20/2012 · Nashua River Rail Trail, Groton Center, Groton, Massachusetts
≈ 4½ × 7" (11 × 17 cm)

8/18/2009 · Nashua River Rail Trail, Groton, Massachusetts
≈ 10 × 17" (26 × 42 cm) ID is uncertain

8/17/2013 · Hopkinton State Park, Hopkinton, Massachusetts
≈ 6 × 8" (15 × 20 cm)

Conyza canadensis description by Thomas H. Kent, last updated 25 May 2020.

7/20/2013 · Wooden Bridge, East Pepperell, Massachusetts
≈ 7 × 11" (18 × 28 cm)

7/31/2012 · Bemis Rd Conservation Area, Pepperell, Massachusetts
≈ 7 × 8" (18 × 20 cm) ID is uncertain

8/20/2012 · Nashua River Rail Trail, Groton Center, Groton, Massachusetts
≈ 7 × 11" (18 × 27 cm)

7/20/2013 · Wooden Bridge, East Pepperell, Massachusetts
≈ 4 × 4" (10 × 10 cm)

7/20/2013 · Wooden Bridge, East Pepperell, Massachusetts
≈ 8 × 12" (21 × 31 cm)

7/31/2012 · Bemis Rd Conservation Area, Pepperell, Massachusetts
≈ 14 × 21" (34 × 52 cm) ID is uncertain

8/16/2013 · Nashua River Rail Trail, Groton Center, Groton, Massachusetts
≈ 7 × 10" (16 × 25 cm)

8/16/2013 · Nashua River Rail Trail, Groton Center, Groton, Massachusetts
≈ 7 × 7" (17 × 16 cm)

8/16/2013 · Nashua River Rail Trail, Groton Center, Groton, Massachusetts
≈ 7 × 7" (16 × 18 cm)

8/22/2013 · Beaver Brook Assn Conservation Lands, Hollis, New Hampshire
≈ 7 × 10" (16 × 25 cm)

Range:

About this map...