Bur oaks have the largest acorn of any species of North American oak that I know of... They are not commonly found in the wild in my area. I have seen some planted specimens that are quite large and old. Most of the acorns I have seen were rather impressive in size as I recall. I do not recall there being any subspecies or cultivars. As with any oak, tree age, health etc can affect the final acorn size.
Bur oaks are a member of the white oak family and thus their acorns are highly preferred by deer and other wildlife.
