Which type of resin is not derived from trees but rather from plant secretions?

Lac is the type of resin that comes from plant secretions, specifically from the secretions of the lac insect, which lives on certain trees. This resin is harvested and processed to create various products, including varnishes, sealants, and colorants. The unique quality of lac is that it is produced by an insect, setting it apart from other resins such as rosin and copal, which are both derived from tree sources.

Rosin is obtained from the pine tree and is used in a variety of applications, including in the production of inks and as a grip enhancer in sports. Copal is also tree-derived resin but comes specifically from the sap of certain tropical trees. Synthetic resins, as the name suggests, are artificially manufactured and not sourced from plant materials directly.

Thus, when considering naturally occurring resins that do not come directly from trees, lac is the clear answer due to its origin from an insect's secretion.