Serruria williamsii, commonly known as the king spiderhead, is a flower-bearing shrub that belongs to the genus Serruria and forms part of the fynbos. The plant is native to the Western Cape and only occurs in the Riviersonderend Mountains.
In Afrikaans it is known as .
The leaves of the plant are whorled below the flowerhead stalk, and are curved upwards. They are dissected, stout, and fleshy, approximately in length and wide. The flowerhead stalk is long. The flowerheads are a panicle of lax (i.e. loose) racemes.