Opposite, simple leaves, round buds, milky sap, pair of samara in line and appear in June.  The leaf disease tar spot (bottom left) common in August and September.  Fall color yellow-brown.  The cultivar ‘Crimson King’ and others similar, has reddish purple leaves and is commonly (and erroneously) called red maple.  Be sure to identify the maple with reddish leaves as Norway Maple.