This is the flower of the kangaroo apple or bush tomato which I'd never heard of before visiting Werribee Zoo recently. I noticed it was growing in abundance in the various enclosures and while on the Open Vehicle Adventure Tour, spotted it growing out in the fields. Rhonda, our driver, kindly advised me of its name.
Some of the fruits were orange but from what I've read they have to be a dark orange to be edible and the green (or unripe) fruit is said to be poisonous. We also saw them growing at the foot of Hanging Rock the following day although all the fruit was green on those shrubs, perhaps because it is a cooler area. I read here that the flowers are hermaphrodite. I haven't found anything to say whether animals eat the fruit although aborigines certainly did and it has a range of medicinal uses as well.