Monsonia spinosa petals are comparatively narrow near the base, sometimes attenuating and leaving visible gaps in the corolla bowl like a dark, five-pointed star-shape among the yellow. The petals are broadest near their tips (obovate). The broad tips are only slightly rounded, nearly truncate.
The lateral margins of the five petals are entire, different from the irregularly jagged upper margins of the uneven, delicately thin blade surfaces.
The dark veins radiating from the base of the petal disappear in the yellow upper part before the tip (Le Roux, et al, 2005; iNaturalist).