apples, (now thought to be 'native' to kazakistan) are found through out the temperate world.

they are stange things, with HUGE genitic diversity. you can't plant an apple seed and expect to get a tree that look like the one the apple came from.

apple trees can grow as tall and sturdy as oaks or they can be shrub-like (there are even varities that are 'ground crawlwers!)

in times past, as caravan's passed throught the forests of kazakistan, they picked up the best apples, (to eat for them selves,) and to trade.. and so apples spread..

here in US johnny appleseed would buy bushel baskets of apple seeds (from east coast established cider mills) and plant them in remote areas.. 10 15 years later when these areas were getting settled, he'd sell the best of trees for profit, (and move further west)

many 'land grant' and settlement agreements required settlers to plant 4 to 10 fruit trees.. and jonny appleseeds trees, grown from seed had survived 10 years or more of winters, summers, floods/droughts--with no attention from him (he planted seeds explored, and planted more seeds..

many trees produced crappy apples, but enough produced apples good enought to eat. (but even apples that didn't taste very good were often useful as animal fodder (pumace) or for making cider (hard cider)

in what remains in the forstest of kazakistan, apples are small (grape sized) to giant (grapefruit!) they come with red, yellow, green, purple skins, that are smooth and textured, thin and thick. the trees are tall, the trees are ground hugging..

Apples genitic diversity, means different areas (europe/US/asia/austrailia) all have apples as a common fruit, and everywhere there are different varities! each area has found trees/fruit that suit its particular climate/tastes.

for more information read Michael Pollen's 'botany of desire' (chapter 1, on apples (or a good part of chapter one) used to be available on line.. a search might yeild it)

as for the fruit being a osage orange, NYC is the northern limit for such trees, (a amall orchard can be found, just inside central park at 96th street and CPW--there are about 10 trees growing together there) the fruit definatly looks more like an orange (a greenish orange) with pebbly, thick leather skin. sometimes apples have 'russeted' skin, and there skin is thick (ish) and textured--but it would be more like pototo (russet potoato) skin than like orange (or osage orange skin.)--not having seen the fruit you found, its hard to tell.. it might well have been an osage orange (search the American Museum of natural history site--they had a small article on osage oranges, about 3-4 years ago. Osage oranges are a native american fruit tree. the range is north of florida (they want one season with definate cool nights and days) but south of NY (they can take some freezing, but not too much..) in NY they tend to grow in protected areas --the group in Central park is protected by the wall (big stones) that sheild them from the worst of the north winds in the winter)