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Tall horseweed is an erect, leafy, many-branched
annual growing to 6' or 7' tall. The herbage is subglabrous to
stiff-hirsute, and the many leaves are alternate, the lower ones being
oblanceolate to 4" long and entire to serrate, and the upper narrower,
sessile and entire. The numerous flowering heads, which appear
in terminal panicles, are radiate, and the 25-40 ray flowers have been
described as inconspicuous. While it is true that
the heads are small, only about 3/16" high, the rays are clearly
delineated as the above photo shows. There are also 7-12 disk
flowers with pappi of dirty-white, hairlike bristles on each head and
involucral bracts which are linear, green, glabrous to slightly strigose,
and have a brownish, resin-filled midvein and subscarious margins. Tall
horseweed is extremely common, typically occupying fields, firebreaks,
and waste and disturbed areas both grassy and bare generally below 6000',
and ranging throughout the United States and southern Canada, and indeed
present ± worldwide. It may be seen blooming from June to September.
Click here for Latin name derivations: 1) Erigeron
2) canadensis.
Pronunciation: er-IJ-er-on kan-a-DEN-sis.
Click here for Botanical
Term Meanings.
Formerly Conyza canadensis.
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