🚀 go-pugleaf

I've helped ID a few mystery plants posted to this group, but now I
need everyone's help myself.

I've been handed a real stumper. 

Collected in Hidalgo Co, Texas.  High-climbing vine without tendrils. 
Leaves alternate (they look opposite in the images, but it's just how
the specimen was pressed), glabrous, with slender petioles to ca. 2 cm
long on flowering branches, blades ovate to slightly reniform, entire,
apically rounded, to ca. 3 cm long.  Flowers in axillary panicles. 
Pedicels minutely bracteate; perianth apparently in one whorl,
4-parted, the parts oblanceolate, whitish, ca. 1 cm long.  Stamens
apparently several to many, the filaments very slender and as long as
or longer than the perianth parts, anthers long, versatile.  Ovary
superior, looks like 3 to 5 recurved style branches; looks syncarpous
but the specimen is dry and difficult to examine.  I have no fruit to
look at.

My first thought was "autumn clematis," but the leaves are simple and
it's not glaringly apocarpous.  It's not Cocculus, and it's not
bittersweet (I don't think).  

Does anyone have any ideas?  This far south, there's always the chance
it's something exotic that has run amok, but you'd think I could suss
it out *somehow*!  

plant, half size
http://botany.cs.tamu.edu/FLORA/pic1/hidalgomysteryhalf.JPG
plant, full size
http://botany.cs.tamu.edu/FLORA/pic1/hidalgomysteryfull.JPG
flowers, x 2
http://botany.cs.tamu.edu/FLORA/pic1/hidalgomysteryx2.JPG
flowers, x 4
http://botany.cs.tamu.edu/FLORA/pic1/hidalgomysteryx4.JPG

Monique Reed
Bio Dept.
TAMU