perianth
flower envelope
[C/U] Both
pl: perianths
This term is used specifically in botanical science to describe the outer envelope of a flower. It serves as a collective designation for the parts that surround the stamens and pistils, regardless of whether those parts are differentiated into distinct sepals and petals. While a casual observer might just see petals, a botanist uses this term to discuss the protective and attractive functions of the floral envelope as a single unit. It carries a clinical, academic tone and is rarely used outside of biological or horticultural contexts.
Countable when referring to the specific envelope of a single flower. Uncountable when discussing the general biological tissue or structure across a species.