Tiny Mystery Plant 2

The tiny mystery plant is not quite as tiny as it was last time. It actually also got a friend now. They are obviously related. I am not quite sure what kind of a tree it might be. All I know so far is that these little buddies have what is called "compound leaves". The larger one of the two plants is now about 5" (13cm) tall. The smaller one is about 3" (8cm). The larger tree has now five compunt leaves, the smaller one has four. Each one of the leaves consists of about 18 oval leaflets which are attached mostly in pairs to about 2" (5cm) long stems.
Both trees have still their thick and fleshy protective leaves attached. Those were used to get throught the soil. I assume that they will eventually fall off. They seem a bit bruised.
The reason why I am writing about the plants now is the fascinating fact that the plants fold their leaves for the night. The leaflets hug the stem very closely and so the look of the plants is very different now. (I am testing them with electric ... they seem to be "waking up" after less than 2 minutes of exposure... okay, do not want jetlagged plants, putting them back into darkness.) It really looks as if they were sleeping. Both are just a few days old, but their complexity is quite incredible.
Ideally, these trees would be Acacia fernesiana, Huicache, Sweet Acacia or Cassie. I know that the tree lives mostly in Texas, Arizona and in Southern Europe, but because I found the seeds near the old Guggenheim estate, it is quite possible that the trees growing there are not really from here... I could probably find out more by digging out the seeds, but I do not really want to disturb these little buddies.
(Will draw them in better .)