Texas Cedar Elm guilds

I'm beginning to design some guilds for planting around our native Cedar Elms Ulmus crassifolia in an area behind the house where the Live Oaks are dying of oak wilt. I'd like to replace the oaks with an understory of edible plants. Thanks to Chris Cromeens, who posted a link to the Texas Plant Information Database http://tpid.tpwd.state.tx.us/index.asp I can look up Cedar Elm and see what species grow in association with it. Obvious edible plants from the list are Elderberry, Common Persimmon, Texas Persimmon, Plum, Black Cherry and Blackberry. For my first guild I'm thinking of using Asian Persimmon in place of the native persimmons, because it does well in Texas and is an attractive small tree. For the shrub layer I want to use Elderberry and Blackberry cultivars. Still pondering the herbaceous, vine, groundcover, and root layers. Not sure if to concentrate on natives, or do a mix of natives and others. In either case, I want to have several edible species.

This guild will be planted in a hugelkultur placed between the driplines of two large elms behind the house, so I will be able to irrigate it during establishment of the trees.

Overstory: Cedar Elm
Understory: Asian Persimmon (probably "Fuyu")
Shrub: Elderberry, Blackberry
Herbaceous: ?
Groundcover: ?
Vine: ?
Root: ?

Any suggestions for plants to use or other input is appreciated.

A few you could try:

agarita - very thorny, but hardy as hell and edible berries. The birds would probably like it. Fragrant flowers for bugs.
Anacacho orchid tree (bauhinia lunarioides) - nitrogen fixer with lots of nice flowers
Texas kidneywood - another nitrogen fixer with nice flowers.

Thank you for those suggestions!