Laennecia coulteri, Coulter's Horseweed
Scientific Name: Laennecia coulteri
Common Name: Coulter's Horseweed
Also Called: Annual Horsetail, Conyza, Coulter's Woolwort
Family: Asteraceae, Sunflower Family
Synonyms: (Conyza coulteri, Conyza coulteri var. virgata, Erigeron discoideus, Eschenbachia coulteri)
Size: 4 inches to 3 feet (5 feet) (10-100 cm (150 cm))
Growth Form: Forb/herb; plants short to tall, multiply stems, glandular and covered with fine white sticky hairs (arachnoid), similar to a spider's web.
Leaves: Green; leaves both basal and cauline; cauline leaves alternate and mostly without a leaf stalk (sessile) and often clasping to the stem; mature leaves oblong, irregular dentition mostly around the leaf base; leaves with minute somewhat bristly hairs and with long soft, straight hairs (hirtellous and (villous).
Flower Color: White with yellow center; small floral heads; inflorescence a raceme; pistillate florets 60 to 100 per head; disk florets 5 to 20 per head; fruit a cypsela with a pappus of white straight stiff hairs (bristles).
Flowering Season: April to October or throughout the year
Elevation: Sea level to 6,000 feet (0-1,800m)
Habitat Preferences: Fields, plains, stream banks and river bottoms, roadsides and other disturbed sites; soils; clay or sandy and often alkaline soils.
Recorded Range: Coulter's Horseweed is found in the southwestern United States and Mexico; in the United States it is found in AZ, CA, CO, NM, NV, TX, UT and in the northern parts of Mexico and in Baja California.
North America & US County Distribution Map for Laennecia coulteri.
U.S. Weed Information: No information available.
Invasive/Noxious Weed Information: No information available.
Wetland Indicator: No information available. In North America Laennecia coulteri has the following wetland designations: Arid West, FAC; Atlantic and Gulf Coastal Plain, FACW; Great Plains, FACW; Western Mountains, Valleys, and Coast, FAC.
FAC = Facultative, occur in wetlands and non-wetlands
FACW = Facultative Wetland, usually occur in wetlands, but may occur in non-wetlands.
Threatened/Endangered Information: No information available
In the Southwestern United States: Arizona and Texas each have 4 species of Laennecia, California, Nevada and Utah each have 1 species and New Mexico has 3 species. All data approximate and subject to revision.
In Southwest Desert Flora also see: Canadian Horseweed, Conyza canadensis.
The specific epithet, coulteri (coul'teri/coulteria'num:) is named in honor of Dr. Thomas Coulter (1793-1843), Irish botanist, physician and explorer. Dr. Coulter was the first botanist to collect in Arizona; (Coulter, Dr. Thomas).
Note this species name recognition should not be confused with John Merle Coulter (1851-1928) who graduated at Hanover College, Indiana, and was botanist to the United States geological survey of the territories in the Rocky mountain system. That Dr. Coulter was honored with the species Erigeron coulteri.