You could be excused for wondering whatever is happening with this daylily bloom. While daylilies normally have three outer sepals and three inner petals, the Quality of Mercy bloom shown above has five of each! This makes for a very full, round flower. Such blossoms are termed polymerous. Formerly, the term ‘polytepal’ was used but ‘polymerous’ reflects more botanically-correct terminology.
Here’s a New Series flower with four petals and four sepals (tetramerous). Below is a Pink Super Spider flower with five of each (pentamerous).
Polymerous flowers can happen occasionally in any cultivar. Some believe the phenomenon is weather-related. However, some cultivars seem especially prone to throwing polymerous flowers. Hybridizers have taken advantage of this proclivity to develop cultivars that produce polymerous flowers 90% or more of the time.
I have one representative of this class of daylilies, bred to produce polymerous flowers. In recognition of this trait, it is named Give Me Eight. Its large, spidery flowers are quite eye-catching.