( Collectively ( , ( petals ( ( form ( the corolla ) ) . ) ) ) )
(ROOT (S (ADVP (RB Collectively)) (, ,) (NP (NNS petals)) (VP (VBP form) (NP (DT the) (NN corolla))) (. .)))
Collectively, petals form the corolla .
(ROOT (S (NP (NP (DT All)) (PP (IN of) (NP (DT the) (NNS petals)))) (ADVP (RB together)) (VP (VBP are) (VP (VBN called) (NP (DT a) (NN corolla)))) (. .)))
All of the petals together are called a corolla.