The five-lobed, tubular calyx of Plumbago tristis simplifies plant identification: The dark red purple sepals are covered in glandular bristles. These hair-like protrusions, called setae are quite conspicuous in this species.
In picture the flowering days are over for now, the corollas withered. The calyces persist around the ovaries where seed is being set. This means that ovules are ripening under cover or zygotes are developing!
All of this follows from multiple events of embryo sacs becoming fertilised by sperm from the male floral parts, the pollen of the species (Vlok and Schutte-Vlok, 2015; Leistner, (Ed.), 2000; Bond and Goldblatt, 1984; iNaturalist; Wikipedia).