One difference seen between this and the Japanese maple is the presence of hairs on the petioles.
Flowers are small, red and yellow colored, emerging with the new foliage but lasting well into full leaf out.
Fruit is a samara, in pairs, each about 1" long, usually at 180 degrees.
Acer palmatum can look very similar. The leaves of the full moon maple are rounded (hence the full moon common name) and the petioles are hairy.
Leaves can look very much like the Vine maple, A. circinatum which is native to parts of CA and north. I think the leaves tend to have more coarsely serrated lobes.