The nut falls out of the involucre when ripe, about 7-8 months after pollination.
From the en.wikipedia.org
A set of bracts forms an involucre surrounding the base of the capitulum.
From the en.wikipedia.org
Typically, an involucre with a clasping shape of a cup or urn subtends each of a thistle's flowerheads.
From the en.wikipedia.org
A crow looks for a nut in a bristly involucre that has fallen from a Turkish hazel tree in Hanover, Germany.
From the washingtonpost.com
Fruits are the matured ovary of seed bearing plants and they include the contents of the ovary, which can be floral parts like the receptacle, involucre, calyx and others that are fused to it.
From the en.wikipedia.org
More examples
A highly conspicuous bract or bract pair or ring of bracts at the base of an inflorescence
A whorl of bracts surrounding or subtending a flower cluster or head or a single flower.
Group of bracts more or less held together as a unit, subtending a flower, fruit (acorn cup), or inflorescence.
A disk-like to cup-shaped, ovoid, or cylindric group of bracts in one or more series that collectively subtend or surround the florets of a head (primary involucre). Involucres are absent in a few genera (e.g. ...
The protective row or rows of bracts surround the florets and receptacle in the capitulum.
A whorl of bracts, often cup-like, at the base of a flower or cluster of flowers.
A whorl or imbricated series of bracts, often appearing somewhat calyx-like, typically subtending the head.
A whorl of small leaves close underneath a flower or flower cluster.
A protective tube of thallus tissue surrounding a single antheridium or archegonium in thalloid liverworts and hornworts.