A 'caulos' is a stem, so 'acaulos' means 'without stem'. This protea has underground stems and the leaves seem to miraculously emerge from the ground. The flowers are not spectacular by comparison with the other protea flowers, since they are unattractive to humans and birds and bees, and use mice for pollination. To help the mice in their cause, the flowers lie on the ground and smell of yeast, especially at dawn or dusk when the mice are most active. In this picture, you can see that one of the flowers has been nibbled by a mouse.
Protea acaulos is one of my favourite plants, because it is so unassuming. It also has very beautiful flower buds, and the yeasty scent of the flower itself is strangely attractive (a pheromone perhaps?). If you are not specifically looking for it, you will struggle to find it nestled between restios and under other shrubs on the ground.