Conyza canadensis  (L.) Cronq.   =Erigeron canadensis   Asteraceae (Sunflower Family)   Native   Horseweed     Common Horseweed

                                          August Photo

Plant Characteristics:  Strict leafy annual up to 2 m. high, sometimes with erect branches in upper half, green, subglabrous to hirsute; lvs. many, the lower oblanceolate, to 1 dm. long, entire or serrate, the upper narrower, sessile, entire; heads small, numerous, panicled; invol. 3-4 mm. high, the phyllaries linear and glabrous or nearly so, with conspicuous oil filled cent. area and narrow subscarious margin; rays 25-40, white, very inconspicuous; disk fls. 7-12.

Habitat:  Common weed of waste ground; throughout the U.S. and s. Canada; trop. and S. America.  Generally below 2000 m. June-Sept.

Name:  Name used by Dioscorides and Pliny for some kind of Fleabane, presumably from the Greek, konops, a flea.  (Munz, Flora So. Calif. 149).  Erigeron is a Greek name meaning "old man in the spring" which may refer to the early flowering and fruiting of many species.  (Dale 62).  Canadensis, the first specimen from N. America came from Canada.  (Dale 13).  Latin, canus, white or Latin, candescen, shining. (Jaeger 44,45). Possibly referring to the white ray fls. 

General:  Very common in the study area.   The photographed specimens were at 23rd Street, Back Bay Dr. at the wet spot just before the hill up to Eastbluff Dr. and on Back Bay Dr. between the Newporter and San Joaquin Hills Dr. (my comments).      C. canadensis has been used for three centuries as a pungent tonic, astringent to check bleeding and as a diuretic.  Claimed to be efficient in diarrhea, diabetics, hemorrhages of the bowels, uterus and of wounds.  For use as an enema, steep a teaspoonful in a quart of boiling water for 20 minutes, use hot, about 112 to 115 degrees F.  (Coon 121).      The leaves and tops can be eaten.  (Heizer and Elsasser 244).       It is reported to be irritating to the nostrils of grazing animals.  (Robbins et al. 462).      A tea from the dried leaves and flowering tops of E. canadensis, treated bronchitis by clearing the accumulated mucus.  Application of these same leaves and flowers will cause an increase in perspiration.  (Fielder 59, 154).      The leaves (not flowers) can be finely powdered and snuffed into the nostrils for acute hay fever with profuse nasal discharge and sore itchy eyes.  An old Navajo treatment.  (Moore, Medicinal Plants of the Desert and Canyon West 23).      The Miwok Indians of central California used E. canadensis as food.  The leaves and new tops were pounded in a bedrock mortar and eaten uncooked.  They were reported to taste like onions.  (Campbell 140).        More than 50 species, chiefly of warmer regions.  (Munz, Flora So. Calif. 149).

Text Ref: Hickman, Ed. 240; Munz, Flora So. Calif. 149; Robbins et al. 462; Roberts 10.

Photo Ref: July 2 83 # 10; Aug 85 # 12,13.  

Identity: by R. De Ruff, confirmed by G. Marsh.  

First Found:  July 1983.

Computer Ref: Plant Data 159.

Have plant specimen.

Last edit 7/30/05.  

                               August Photo                                                                    August Photo