Cylindropuntia ramoissima flower bud - 'cactella'

Cactus flower is not a true flower, but a meta-morphed sprout, or stem. It is very clearly seen on C. ramoissima example. At early stage of development new flower and new stem are very hard to tell apart, and it is likely they are not different at first, with sprout turning to bud in response to some plant hormones. In my observation, in the greenhouse culture C. ramoissima produces flowers only when in spring time, after the new growth has started, I stop watering plants. That might be an adaptation to grow as much stems as water supply permits this year, and produce flowers once rains has stopped.
The special botanical term 'cactella' was coined to signify this specific feature of flowers in Cactus family. That is, A.Doweld introduced this term as a name for this cactus-specific stem-flower and stem-fruit organ.