spike

n. an unbranched inflorescence of sessile or subsessile flowers, maturing from the bottom upwards
compare with a raceme in which the individual flowers are stalked (have pedicels)

spadix

n. a spike with small partially embedded flowers on a thickened fleshy axis in the Araceae, this is usually subtended by a spathe

floret

n. a small individual flower of a cluster, as in the head of the Asteraceae or the spikelet of the Poaceae

raceme

n. an elongated compound inflorescence that is unbranched and with the pedicellate flowers maturing from the bottom upward
compare with a spike, in which the individual flowers are sessile or subsessile