These are **stellate** ("star-shaped") [and possibly **peltate** ("borne on a stalk")] **hairs** (" **trichomes "**) of the leaf itself.
* From Harris & Harris's (2001) ""Plant Identification Terminology: An Illustrated Glossary":
> **Peltate**. a flat structure borne on a stalk attached to the lower surface
> **Stellate**. Star-shaped, as in hairs with several to many branches radiating from the base. Figure 1686.
 showing stellate, peltate trichomes. SOURCE: Nickrent, D.L., Costea, M., Barcelona, J.F., Pelser, P.B. & Nixon, K. (2006 onwards) PhytoImages. Available from: