Thank you for this useful comment. As a side note regarding the common name, it was apparently invented after the fact based on a misunderstanding. The gory details below.

This species was named after its European discoverer, Susanna Charlotta Louisa Muir, so if anything this plant should be called Susanna's spurge. She was the wife of noted South African naturalist John Muir, who was born and educated in Scotland.

http://www.s2a3.org.za/bio/Bio...

To be honest I don't know if anyone except the internet echo chamber (and its real world followers) actually uses that common name (with a z) for the plant.

Muir's wife was also the inspiration for two other species names, Protea susannae and Thesium susannae, and the spelling is consistent across all 3.

Thanks for the useful info. Now I'll return the favor.

Unless there are two naturalists named John Muir, born in Scotland, he's an American naturalist, not a South African one. Now his wife might be South African, though it seems unlikely, since he met and married her in California.

John Muir the American writer (1838–1914) is distinct from John Muir the South African naturalist (1874–1947), though they were both born in Scotland.

https://en.wikipedia.org/wiki/John_Muir_(disambiguation)