Pharnaceum aurantium buds suggest white petals under the receding brown sepals. This is misleading, as the visible white parts are sepal margins, attached to the brown exterior; there being only sepals here and no petals.
The sepals are attached to each other at the base around the flower stalk only, separating higher up to spread widely as the flower opens. They do this only in the late afternoon (Vlok and Schutte-Vlok, 2010; Manning and Goldblatt, 1997; Bond and Goldblatt, 1984; Leistner, (Ed.), 2000; iNaturalist).