A Plant called "Twin-leaf"

Roepera apiculata (Zygophyllum apiculatum)
Family: ZYGOPHYLLACEAE
Here’s an interesting plant, in flower in Irongate Environmental Reserve at present. It looks quite out of place, so softly fresh and green in such a dry area and at such a dry time of year.
It’s a short-lived perennial which grows in drifts and patches, getting to about a foot high. It self-seeds readily, so patches can persist indefinitely. The leaves refresh themselves annually in late winter.
Bright yellow butterflies were showing great interest in the patches of twinleaf. Perhaps it was the flowers they were welcoming. Nectar must be in rather short supply at present. Perhaps they were also egg-laying, though I found no caterpillars and am not aware of this as a known butterfly host plant.
The seeds will be followed by pretty, green five-winged seed capsules, each with five shiny black seeds inside.
Twin-leaf looks as though it would be a good pasture plant, and is yet another of the native plants which has an undeserved reputation for toxicity to stock. Like all Australian plants suspected of causing problems for pastoralists, it has been carefully researched, and the finding is that stock simply refuse to eat it in its green state. It’s a different story once it’s old and dry, however, when sheep will eat it happily, and with no ill effects.
I suspect that the natural occurrence of this plant would act as a soil pH indicator, as I only know if it growing in places where the soil is alkaline.