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Keys
Vascular plant groups
Club mosses
Ferns
Vegetative key to families
Gymnosperms
Flowering plants
Genera
Families
Asteraceae
Flowers grouped into heads
Asteraceae
consider the other alternative
Involucral bracts of the female heads or of the outer florets enclosing the fruit(s) at maturity and forming a
burr
(Fig. 42)
consider the other alternative
Burrs with hooked appendages
choose this alternative
reject this alternative
Burrs 5–8, whorled, each burr derived from a single
ray
floret
enclosed in a
bract
Acanthospermum
choose this alternative
reject this alternative
Burrs solitary or few together in the axils of
alternate
leaves, each
burr
containing 2 fruits
Xanthium