I think Laura is correct. The photos you have attached look like Seena septemtrionalis. Where I live in Northern NSW, Australia it is commonly called Smooth Senna and is considered a weed as it invades native rainforests and competes with native plants for food, light and water. If you do allow it to grow care shoud be taken to prevent it spreading. All the seed pods should be removed and destroyed ,they will ripen off the bush so must be properly destroyed and not dumped. Any prunings from the tree should also be destoyed as the plant will easily grow from cuttings left lying around. Unless you are attched to the plant I would pull it out and plant something else in it's place that does not have the same weed potential.
Senna septemtrionalis - BRAZILIAN BUTTERCUP. Previously called "Cassia floribunda".
Fixes Nitrogen and was planted extensively by Permaculturists (incl. Joe Polaischer).
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Fixes Nitrogen and was planted extensively by Permaculturists (incl. Joe Polaischer).
Lately the Auckland regional Council takes a dim view of it:
http://www.arc.govt.nz/environment/biosecurity/search-for-plants/in...
I have found that it regenerates even through very thick (=never mowed) kikuyu ...