AusBonsai

Can anyone identify this bush, it's similar to a firethorn bush however they're absent of thorns, very dark, almost black bark.

Is it cultivated or growing in its natural environment? If so where?
Is there any spent flowers or fruits on the ground below the tree?
I think perhaps it’s Dodonea viscosa

They were possibly planted but I think they're pretty much wild, fairly common around here, Southwest Vic. Its an old area though so they could be pests or trees council used at some stage.

These ones are growing in a stand beside the train line, they grow into a small tree, multiple long branches with foliage around the outside but backbud readily at the base.

This looks soooo much like a Lycium ferocissimum, the African boxthorn or boxthorn.
African boxthorn, however, do have thorns. I'm not aware of a thornless variety.
Your first image shows where the small flowers, shown in the image below, would have been.
"African boxthorn is a large shrub which grows up to 5 metres (16 ft) high and is covered in spines.
The leaves are oval in shape and are 10–40 millimetres (0.39–1.57 in) long and 4–10 millimetres (0.16–0.39 in) in width.
The solitary flowers emerge from the leaf axils and are purplish." - Wikipedia

I've been growing a stump as a bonsai. It seems to stand my "far from expert" care without missing a beat. No problem with pruning, root work, seems to take everything in its stride. I'm careful to burn any prunings as it is a declared noxious weed.

When I pop the pics in plantID most come back Dodonea viscosa as Dendrophile Dave suggests, after searching the bark I think that might be correct. The plantID page has been invaluable, generally puts me pretty close, then out of the blue spits something like Australian Blackthorn out.

Hard to kill the boxthorn Jan, not sure how long they live though, might not be able to pass it to the kids.

Definitely a Dodonaea species as treelover said. Dodonaea viscosa subsp. spatulata to be precise. They appear to be flowering so should be producing seed soon.