Glabrous:  Having no hair.

Gymnosperm:  A plant that bear ovules on special structures (like the scales of a cone) rather than enclosed in an ovary.

Gynostegium: A specialized organ formed by the fusion of the stamens and stigmas (common in milkweeds).

Head:  An inflorescence comprised of a dense cluster of stalkless flowers.  Example: clover, daisy.

Helicoid cyme:  An inflorescence with flowers on one side of the central axis.  The entire structure coils to forma  spiral

Hood: In milkweed flowers, a boat-shaped part of the corona (a structure that rises above the true petals.)

Horn:  In milkweed flowers, an appendage arising from the hood of the corona (a structure that rises above the true petals.)

Imbricate:  Overlapping (referring to scales on a bud).

Inflorescence: A flower cluster.

Lanceolate:  Lance-shaped; much longer than broad.

Leaflet:  One segment of a compound leaf.

Leaf scar:  The mark left on a stem once the leaf has fallen.

Legume: A fruit derived from a single ovary and which opens along two longitudinal sutures.  Example: pea, bean, honeylocust.

Lenticel:  A raised marking found on the stem.  It functions in gas exchange.

Lobe: a projecting part or segment of a leaf whose margin is divided by sinuses.