I found this Vachellia species with thickend thorns on a little island in the River San Carlos, appr. 7km north of the border between Costa Rica and Nicaragua - where the San Carlos river joins the San Juan river. Province Alajuela, Nov. 2008.
The elevation is less than 50 m above sea level.
I could only rip off a twig and photograph it in the small boat.
The leaf is 11 cm long (1 cm petiole, 10 cm rachis), with 15 pair of pinnae and more than 30 leaflet pairs per feather. On the petiole there is a thick green gland. Between all pair of pinnae there are little round glands.
At first I thought it to be V. melanoceras. But now I enlarged the petiole section and recognized only one gland there. IProf. D.Seigler identified the spoecies as Vachellia ruddiae.