I thought mine was Makino Korean clover (aka Korean Bushclover), but a few weeks ago, jekeesl posted the difference between that and Japanese Bushclover, and mine is definitely Japanese Bushclover (formerly Japanese Lespedeza).

The two Kummerowia species you might see in the States are K. striata (Japanese Bushclover) and K. stipulacea (Korean Bushclover). K. striata leaves are on very short petioles, and K. stipulacea leaves have petioles 4-10 mm long (averages about 1/4 inch). If the stems are also quite hairy, with hairs appressed toward the stem base, then you probably have Japanese Bushclover. If the stem hairs are sparse, it's probably Korean Bushclover. Yours looks more like K. striata to me.

http://forums2.gardenweb.com/forums/load/namegal/msg0719474610565.html

That's it, TYVM! Certainly the most interesting pavement crack plant I've seen in a while.

Be glad it was just a pavement crack and not in half your lawn!

So now I know what it is. Never had an ID.
Appears the globe is all one and no boundaries when it comes to weeds as I've had this stuff in what passes for "lawn" here for ages.
And I definitely second missing's opinion!

Well, part of Mom's lawn isn't lawn at all, it's just bare, completely baked, sandy nothingness. If this plant can grow there, hopefully it will. Grass isn't the end-all, be-all of mowed areas, not tough enough to grow in that spot. Also noticed some of this plant in areas of very sparse grass. From farther away, it just looks 'green.' But close up, it's apparent that without the Kummerowia, it would look like mostly sand with a slight rash of grass.

I understand the "Well, at least it's green" -- having been known to say that myself on many occasions! -- but here, the Kummerowia is bent on total conquest. (It'll be interesting to see who eventually wins the shade wars, the Kummerowia or the Green kyllinga....)