You all that live much closer to Dallas might visit documentation of this historic institution, where there ARE likely more images.
I did a cursory internet search for this school, and found that there is more than a bit of information out there. I didn't find any pictures that categorically defined what is planted there, but there are photos of the front of the school with the flagpole showing the landscape - just not close up.
Texts like yearbooks would be where I'd begin the search. Those usually have all kinds of pictures from the school and its grounds.
You need a sleuthing/scavenger hunt forum, for instances like this...
