6D: Nut with a cupule (ACORN) - remembered this feature from some earlier discussion we had about the word "cupule".    From Wordnik.com.  [Rex Parker Does the NYT Crossword Puzzle] Reference

A common form of prehistoric rock-art here in California is the cupule.    From Wordnik.com.  [Cupules and Geophagy] Reference

Cohesion of the bracts by their edges, so as to form a tubular involucre, or by their surfaces, so as to form a cupule, is not of uncommon occurrence, under natural conditions, and may be met with in plants which ordinarily do not exhibit this appearance.    From Wordnik.com.  [Vegetable Teratology An Account of the Principal Deviations from the Usual Construction of Plants] Reference

PS (2008) Molecular phylogenetics and cupule evolution in Fagaceae as inferred from nuclear CRABS CLAW sequences.    From Wordnik.com.  [PLoS ONE Alerts: New Articles] Reference

Inflorescence appearing with the leaves in spring; sterile catkins from terminal or lateral buds on shoots of the preceding year, bracted, usually several in a cluster, unbranched, long, cylindrical, pendulous; bracts of sterile flowers minute, soon falling; calyx parted or lobed; stamens 3-12, undivided: fertile flowers terminal or axillary upon the new shoots, single or few-clustered, bracted, erect; involucre scaly, becoming the cupule or cup around the lower part of the acorn; ovary.    From Wordnik.com.  [Handbook of the Trees of New England] Reference