Identifying Ash-leaved Maple, Acer negundo, came bits at a time. The tree in question is on a busy road without sidewalks and its low-hanging branches force me to wait for a break in traffic. With an eye out for speeding vehicles with operators wired to cell phones, I don't get to casually befriend this species.
I first noticed these leaf stalks on the ground surrouding this tree. They look like little bones, don't they?
Over time, I discovered these were petioles for compound leaves that looked like ash. That is, except for the leaves that looked strangely like deformed maple. So there it is, a tree seemingly assembled from parts of other trees! :-)
In this shot below we can see the petioles remaining after the leaves have dropped--a two part process to shedding leaves.
From American Forest Trees:
"Attempts to ascertain the meaning of the word negundo which botanists apply to this species have not been crowned with entire success. It is known to be a word in the Malayalam language of the Malabar coast of India, and is there applied to a tree, apparently referring to a peculiar form of leaf. The name was transferred to the box elder by Moench, and has been generally adopted by botanists, although at least seven other scientific names have been given the tree. It bears ten or more English names in different regions. Among these names are ash-leaved maple, known from Massachusetts to Montana and Texas; cut-leaved maple in Colorado; three-leaved maple in Pennsylvania; black ash in Tennessee; stinking ash in South Carolina; sugar ash in Florida; water ash in the Dakotas; and box elder wherever it grows."
More from From American Forest Trees:
"There is no good reason why this tree should be called an elder, or an ash, except that its leaves are compound. If that is a reason, it might be called a hickory or a walnut, since they bear compound leaves. It is clearly a maple. Its fruit shows it to be so, and Indians of the far Northwest who had no other maple, formerly manufactured sugar from this tree, collecting the sap in wood or bark troughs and boiling it with hot stones.
"The compound leaf does not necessarily take it out of the maple group. It requires no great exercise of imagination to understand how a lobed leaf, by deepening the sinuses between the lobes, might become a compound leaf in the process of evolution. There may be no visible evidence that the box elder's leaf reached its present form by that process, but there is another maple which is at the present time developing a compound leaf in that way, or seems to be doing so. It is the dwarf maple (Acer glabrum) of the Northwest coast. Lobed leaves and compound leaves may occur on the same tree."
Gibson, Henry H. American Forest Trees. Chicago, 1913. 445-6. Web. Google Book Search. 13 Oct 2009.