Definition of involucre in English:
 involucre
noun ˈɪnvəl(j)uːkəˈɪnvəˌlukər
1Anatomy 
A membranous envelope.
2Botany 
A whorl or rosette of bracts surrounding an inflorescence (especially a capitulum) or at the base of an umbel.
 Example sentencesExamples
-  The cupules are simple involucres of bracts which are spirally arranged (according to a Fibonacci pattern) on the floral axis preceding the flower.
 -  Basal leaves and flowers initiate from a tuberous rhizome and three green cauline leaves arranged in a whorl form an involucre around the developing flower.
 -  We used to help my grandmother gather the flowers, remove the green involucre from beneath the flowerhead and separate the rays, or florets.
 -  All flowers are enclosed within an involucre with four marginal glands.
 -  The Hermaphrodite cyathium shows the characteristics measured (length and width of the cyathium involucre and the nectary).
 
Origin
  
Late 16th century: from French, or from Latin involucrum, from involvere 'roll in, envelop' (see involve).
   Definition of involucre in US English:
 involucre
(also involucrum)
nounˈɪnvəˌlukərˈinvəˌlo͞okər
Botany A whorl or rosette of bracts surrounding an inflorescence (especially a capitulum) or at the base of an umbel.
 Example sentencesExamples
-  The cupules are simple involucres of bracts which are spirally arranged (according to a Fibonacci pattern) on the floral axis preceding the flower.
 -  All flowers are enclosed within an involucre with four marginal glands.
 -  The Hermaphrodite cyathium shows the characteristics measured (length and width of the cyathium involucre and the nectary).
 -  Basal leaves and flowers initiate from a tuberous rhizome and three green cauline leaves arranged in a whorl form an involucre around the developing flower.
 -  We used to help my grandmother gather the flowers, remove the green involucre from beneath the flowerhead and separate the rays, or florets.
 
Origin
  
Late 16th century: from French, or from Latin involucrum, from involvere ‘roll in, envelop’ (see involve).