Should thank you be sent when dinner party and guest brings flowers?

If you had previously sent a formal invitation inviting them to your dinner, then it would be appropriate to send a brief thank you note for their having attended, along with an addition of thanks for the lovely gesture of flowers and how much they brightened your home.

However, if the invitation to attend was verbal and the individual brought flowers, it is a less formal environment and would not be necessary. Nevertheless, it is always nice to be thanked, so perhaps a quick telephone call to thank them would be kindly received.

Personally, I never arrive to a private event without a small gesture of greeting, such as flowers, candies, or where appropriate champagne or wine.