Schizoglossum bidens subsp. bidens flowers

The flower of Schizoglossum bidens subsp. bidens has at its back an acutely five-pointed olive green calyx, showing tiny spiny protuberances halfway up the sides of some of the sepals. There is also a hint of purple or maroon on the sepal tips. The curiously lined oblong, green corolla lobes with their bi-lobed or wedge-shaped tips, are topped by another five-pointed structure, the white two-tier corona. 

The neat geometry here is more than art: It is botany at its creative best in one of the Apocynaceae family's structural masterpieces (Pooley, 1998; iNaturalist).