Again, a thank you to Katy S for sharing her photographs with us. This is the third in a series of six (or more!) featuring plants of Australia. Much appreciated!
I first have to mention I find this photograph reminiscent of last week's Isomeris arborea, particularly in terms of colour. Interesting, perhaps, that both the bladderpod spiderflower and this, the bent-leaf wattle, are species of dry, sunny habitats. Other similarities exist: leaf shape, habit (both are shrubs) and glaucous leaves (covered with a waxy coating, in this case causing a whitish colour). All in all, this is a textbook, if unspectacular, instance of convergent evolution: the accumulation of similar traits occurring in independent species as a result of adapting to similar ecological niches.
Where the two species diverge, e.g., in the flower shape and structure, it is generally safe to assume that dissimilar ecological conditions exist. Acacia flexifolia, like many wattles, is insect-pollinated by beetles, wasps and bees. Isomeris arborea, on the other hand, is visited by hummingbirds and bumblebees. Of course, it isn't as simple as that (if it was, there'd be fewer variations in flower shape and structure) – genetic barriers and restraints, along with additional ecological factors, contribute to the difference.
Photography / biology resource link: 16 Mind-Blowing Microphotographs of Living Things, suggested by Stannous F. Thank you!