 The monoecious ( or bisexual ) yellow @-@ green flowers are produced after the leaves in early summer , in May or June in the British Isles , on pendulous panicles 10 to 20 cm ( 4 to 8 in ) long with about 60 – 100 flowers on each stalk . The fruits are paired winged seeds or samaras , the seeds 5 to 10 mm ( 0 @.@ 2 to 0 @.@ 4 in ) in diameter , each with a wing 20 to 40 mm ( 0 @.@ 8 to 1 @.@ 6 in ) long developed as an extension of the ovary wall . The wings are held at about right angles to each other , distinguishing them from those of A. platanoides and A. campestre , in which the wings are almost opposite , and from those of A. saccharum , in which they are almost parallel . When shed , the wing of the samara catches the wind and rotates the fruit as it falls , slowing its descent and enabling the wind to disperse it further from the parent tree . The seeds are mature in autumn about four months after pollination . 
