So many of the plants we regard as weeds came from Europe along with the colonists and their seeds and livestock. This weed is a native American variety. Call it horseweed, mare’s tail or hogweed, it’s tall and prolific.
Very small flowers are easier to show in pairs so the front and side views are in the same picture.
Conyza canadensis Cronquist
June to November N Family: Asteraceae
Flower: The many-branched flower panicle can be 18 inches tall and spread out over 6 inches with a flame shape. Each flower is cylindrical. The half inch long cylinder is made up of dark green, overlapping bracts. From 25 to 45 white ray flowers radiate out an eighth of an inch around the top of the cylinder surrounding numerous tube flowers.
Leaf: Alternate leaves can be so dense as to appear whorled. Each leaf is 2 – 3 1/2 inches long but less than 1/2 inch wide. There is a midvein and thick edges. White hairs stick out along the edges. Top and bottom are dark green.
Stem: The single stem can reach 7 feet. It is light green with white hairs. It is stiff.
Root: The annual root is a short taproot with fibrous roots.
Fruit: The seeds are an eighth of an inch long and thin with short, white threads sticking out one end.
Habitat: This plant prefers full sun and disturbed areas such as roadsides and barnyards.
Canada Fleabane, Hogweed, Mare’s Tail
Horseweed is a native weedy species. It produces hundreds of seeds which are wind disseminated. The plants often come up in dense stands.
The young stem growing up can be mistaken for a goldenrod. Once the flower stalks appear, horseweed is unmistakable.
In poor areas horseweed can be short, only a couple of feet tall. In better soils and with enough rain, the stems can reach seven feet with massive flower heads. If you can overlook the facts that few animals other than insects eat these plants and their sheer numbers can make them a nuisance, the tall, flowering plants are impressive.
The plants seem to prefer growing along fence lines or near sheds. They can grow in shade but do best in full sun.
Wind can make a group of horseweeds seem to ripple as the stems dip down and stand back up. The stiff stems can take a lot of wind without being uprooted. It takes pressure to snap the stems.
Each plant matures, flowers, seeds and dies over a few months. New plants replace the older ones to keep the blooming time so long. The leaves yellow and drop off from the bottoms of the stems as seed heads replace the flowers until only the stalk is left devoid of flowers, leaves and seeds.
For the serious amateur botanist, check out the book The Syrian Milkweed to find out more about how plants get their names and how the process can make mistakes.