The arrangement of the trident-shaped seeds into globoid seedheads is very striking. The common name derives from the appearance of these seeds. Among the many Bidens spp. in Illinois, Spanish Needles is the oddball of the group. The seeds of Spanish Needles are longer and usually more slender than those of other Bidens spp. Spanish Needles also has differently shaped leaves – they are more pinnately divided into smaller leaf segments than the leaves of other Bidens spp. (which are sometimes simple, rather than compound). Finally, Spanish Needles seems to prefer drier habitats; other Bidens spp. are more likely to be found in various wetland habitats.
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