Pachycarpus vexillaris, commonly known as mountain thickfruit and previously as Asclepias vexillare and Xysmalobium vexillare respectively, is a branched perennial growing stout, erect stems to 30 cm in height.

The species distribution is in the north of the Eastern Cape around the southern end of the Drakensberg Mountains to Barkly East, Aliwal North to Graaff-Reinet in the Camdeboo and into the northeast of the Western Cape Karoo around Beaufort West. The photo was taken near Rhodes in January.

The habitat is montane grassland and Karoobossieveld where the rain falls in summer and temperature extremes often challenge. The species is not considered to be threatened in its habitat early in the twenty first century (Leistner, (Ed.), 2000; JSTOR; iNaturalist; http://redlist.sanbi.org).