Tribulus terrestris, Tribulus micrococcus.
These two pretty yellow-flowered annuals are making colourful summer splashes at present, on the black soil plains west of Toowoomba
One is a native plant. The other introduced.
They are somewhat similar looking, but have some obvious differences which make it easy for us to know which one we’re looking at.
Barefoot country children have no trouble telling us which one is Tribulus terrestris, variously known as caltrop, bull-heads, catheads, or goatheads. It’s seedheads, which are just beginning to form now, break into sections when ripe. Each section has three wicked sharp points. No matter how they fall, one always points upwards, often causing pain to people and animals.
Caltrop is the smaller of the two plants, and has smaller flowers. It tends to hug the ground, in a rather open network. It is originally from the Mediterranean, but has become naturalised all around the world.
The native Tribulus micrococcus, known as yellow vine or spineless caltrop, is a larger, showier plant with bigger flowers.
Close-grown groups tend to form a dense, ground cover.
Neither of the plants is good for livestock. An excess can poison animals, especially when they have responded to rain with rapid, lush, leafy growth. Farmers also find that they grow rather too easily and can be weeds in their cultivations.
However, those of us who don’t have to worry about that, can enjoy them as part of the wildflower display which always makes our blacksoil plains so beautiful at this time of year.
I’ve never heard of gardeners growing either of them on purpose, though it could, no doubt, be done. Perhaps yellow vine has the potential to become a favourite easy, self-seeding plant, popping up each year and delighting the gardener. Don't do it where it might escape and pose a threat to livestock, though.