Hairy Horseweed
Asthma-weed
Conyza bonariensis
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Growing in a crushed-rock xeriscape bed despite nylon mesh mulch below the stones. Glendale, Arizona, USA. July 2010.
ANNUAL: Herbaceous summer annual germinating from seed by mid spring and
persisting through summer, depending on available moisture. Surprisingly able
to grow with very little moisture. Generally with a few upright stems
occasionally exceeding 50 cm tall.
FLOWERS: Numerous small flower heads remain mostly closed up with just a
bit of white bristles appearing above the bracts. The bract tips may appear
purplish.
LEAVES: Leaves and stems are covered with long silky hairs giving the
plant a silvery appearance. Leaves are elyptic to linear, usu. with several
teeth on the margins.
RANGE: Frequent weed in alleyways, ditch banks and in even xeriscap
urban gardens. Sometimes in washes in natural desert areas.
FRUIT: Heads produce abundant, single-seeded achenes topped by fine
bristles that serve to distribute seeds via wind.
UNARMED. Without thorns.
Two insects are sometimes abundant on this
plant.
Seed Bugs feed on developing seed heads and
lace bugs are sometimes so abundant as to defoliate plants.