corolla
noun
co·rol·la kə-ˈrä-lə 
-ˈrō-
-ˈrō- : the part of a flower that consists of the separate or fused petals and constitutes the inner whorl of the perianth
corollate
kə-ˈrä-lət
adjective ˈkȯr-ə-ˌlāt
ˈkär-
Example Sentences
Recent Examples on the Web The bird’s beak evolved to gather nectar from flowers with long tubular corollas, including a passionflower that is deeply reliant on the avian rapier for pollination. 
National Geographic, 18 Apr. 2018 Double Otto’. The 2-inch-wide double flowers feature deeply flared scarlet sepals with double, dark-purple corollas. Ciscoe Morris, The Seattle Times, 14 June 2017
National Geographic, 18 Apr. 2018 Double Otto’. The 2-inch-wide double flowers feature deeply flared scarlet sepals with double, dark-purple corollas. Ciscoe Morris, The Seattle Times, 14 June 2017 Word History
Etymology
borrowed from New Latin corōlla, going back to Latin, "small wreath of flowers, garland," by syncope and assimilation from *korōn-ela, from corōna "wreath, garland worn on the head as a mark of honor or emblem of majesty" + -ela, diminutive suffix — more at crown entry 1
First Known Use
circa 1753, in the meaning defined above
Kids Definition
corolla
noun
co·rol·la kə-ˈrä-lə
: the part of a flower that is formed by the petals