Spike

A central rachis bearing a number of sessile flowers

Catkin

A dense spike bearing many apetalous, unisexual flowers

Raceme

A central axis bearing a number of pedicelled flowers; all pedicels are about the same length

Panicle

Diffusely branched rachises with many flowers

Cyme

A central rachis terminated early by a flower and lateral branches

Umbel

Usually flat topped, with many pedicels arising from a common point at the top of the peduncle

Head

A number of sessile flowers clustered on a common receptacle that may be flat-topped