My point is that acer IS used like oak or pine. I'm well aware of the Latin names of oak and pine; I could give you the "proper" name of every plant that grows on my land. I would, however, write that most of the acers I have are A. rubrum. Did you see the link I posted? Oaks and acers and beeches? Do you argue with Oxford?
Chambers, too, has acer in lower case, as a plant of the genus Acer, just as one would say that oak is one of the genus Quercus. No, I've never heard of maples. How insulting can you be?