Berkheya purpurea leaves have sturdy midribs, especially in their lower parts where the midribs are purplish in the photo. The midrib colour changes to white higher up as it reduces in size, until only the fold is visible where it runs to the tip.
The youngest, short leaf in the centre shown here has additional woolliness beyond the hairiness typical of mature leaves.
These plants grow fast and last long, growing from a strong taproot and forming clumps. The species is not considered threatened in habitat early in the twenty first century (www.kew.org; Manning, 2009; www.plantzafrica.com).