Spinescent, ending in a spine or rigid point.
Spinulose, with diminutive spines.
Spur, a usually slender tubular process, from some part of a flower, often honey-bearing.
Staminate, having stamens, but no pistils.
Staminodium, a sterile stamen, or something taking the place of a stamen.
Stellate, star-shaped.
Sterile, barren; incapable of producing seed; a sterile stamen is one not producing pollen.
Striate, marked with fine longitudinal lines.
Subtended, supported or surrounded; as a pedicel by a bract, or a flower-cluster by an involucre.