Segment. One of the divisions into which a plane organ, such as a leaf, may be divided.
Sepal. A calyx leaf.
Serrate. With teeth inclining forward.
Serrulate. With small teeth inclining forward.
Sessile. Not stalked, as when the leaf blade or flower rests directly upon the twig.
Simple leaf. Not compound, having one blade not jointed with its stem.
Sinuate. Strongly wavy-margined.
Sinus. Interval between two lobes or divisions of a leaf; sometimes sharp-angular, sometimes rounded.
Spatulate. Gradually narrowed downward from a rounded summit.
Spike. A cluster of sessile or nearly sessile lateral flowers on an elongated axis.