Acmadenia macropetala is a small, single-stemmed shrub that spreads, reaching about 50 cm in height. The loose, hairless branches have grey-brown bark showing scars of leaves that have dropped off. The slender, upper stems are finely hairy and branch much.
The small, simple leaves are decussate and sessile. They overlap densely in picture, sometimes less so, showing a little bit of stem or four neat, vertical leaf arrays. The leaf-shape is lanceolate to ovate, ending in a pointed tip. A fine hair fringe is present on the margins of the deep green to dark green, gland-dotted blades. Leaf dimensions are about 3,5 mm long and 1,5 mm wide.
Pink flowers grow solitary at stem-tips and from the forks of upper branchings. The specific name, macropetala, meaning large petals, refers to the flower. The five spreading petals have central, dark lines as nectar guides. Flowering happens in winter.
The species distribution is in the Western Cape from Bredasdorp and along the Langeberg Mountains as far east as Cloete’s Pass.
The habitat is sandy and loamy fynbos on lower slopes and on quartz outcrops. The species is deemed vulnerable in its habitat early in the twenty first century, due to poor fire management, alien vegetation, overgrazing and habitat loss from crop farming (Curtis-Scott, et al, 2020; Vlok and Schutte-Vlok, 2015; Bond and Goldblatt, 1984; iNaturalist; http://redlist.sanbi.org).