Can it definitively be said that this is an Acacia

I have my doubts, since this tree appears to be different than the Acacias I have seen. Street tree medium size in the city of Medellin Colombia 1400 meters

 

For something similar (but not this species), look up Acacia dealbata. That one has similar leaves, but more flower clusters per inflorescence.

 

But am I save calling this an Acacia?

 

I doubt that you are "safe" in calling this an Acacia. Firstly, you need to look more closely at the individual flowers (not the whole spherical head of flowers) and pull one apart to see if the stamens are fused into a tube at the base. If they are very distinctly fused, then it's not an Acacia. Also, my impression is that the corollas visible in your 4th photo are much longer than you generally get in Acacias.

But another complication: so far I have used "Acacia" in its traditional sense, but those with leaves and inflorescence looking like this have now been placed in new genera, including all the tropical American species. See this Wikipedia article - http://en.wikipedia.org/wiki/List_of_Acacia_species

If it is an 'Acacia' (in the broad sense, with stamens not fused), then I think it would likely now be in genus Vachellia.

But if it's not an 'Acacia', You would need to start looking in other Mimosoid genera. I would start with Albizia, which has many species in the tropics including the Americas. Unfortunately it's unrewarding to do a picture search of Albizia because about 99% of the pictures you get are the popular and cold-hardy A. julibrissin.

 

Thanks Tony I did some searching and I could not find a match. I will stick with Fabaceae to be safe. Would this tree

http://www.botanicalgarden.ubc.ca/forums/showthread.php?t=83626 also be in the same family?

 

Yes, I saw that one previously and could not be sure. It's one of the Caesalpinioid legumes (i.e. in subfamily Caesalpinioideae, whereas Acacias, Albizias and the like are subfamily Mimosoideae).

The flower structure is wrong for the Cassi-Senna group. I would be looking at the genera Peltophorum and Caesalpinia. The latter is very diverse in growth-form as well as leaf and flower features.

 

Thanks Tony family or subfamily is good.