Linked from
The 15 pages that link to Capitulum, each with the reason it gives.
InflorescenceBroader topic: The apparent single flower head is actually a cluster of many flowers.
InvolucreBroader topic: The involucre forms the conspicuous outer cup beneath a capitulum.
AcariBroader topic: Its barbed mouthparts anchor ticks during blood meals.
AchilleaBroader topic: Each Achillea flower head is a capitulum, not a single flower.