Simple (simplex). Without branches; or without segments jointed to the rachis.
Smooth (laevis). With an even surface (without protuberances).
Spadix (spadix). A spike with a thick axis and inconspicuous flowers, usually enveloped by a spathe.
Spathe (spatha). A large bract more or less enveloping a flower or inflorescence.
Spatulate (spathulatus). More or less rounded above and tapering towards the base.
Spike (spica). A centripetal (racemose) inflorescence with an elongated axis and sessile or nearly sessile flowers.
Spikelet (spicula). A spike-like partial inflorescence.
Stamen (stamen). A modified leaf bearing the male reproductive cells (the pollen).
Staminode (staminodium). A barren stamen (without anthers or with incompletely developed anthers).
Sterile (sterilis). Barren, i.e., without well developed ovules or pollen.