In Kate Greenaway's Language of Flowers, the entry for Agrimony reads: Thankfulness. Gratitude.
A clear expression of thanks
The paired words in the agrimony entry reinforce one another rather than introducing two opposing messages. That makes the reference useful when discussing gratitude in this particular dictionary. It does not establish a rule about which flowers people should buy for a thank-you gift.
For a card, connect the reference to something specific: help with a move, patient advice or thoughtful company. Naming what you appreciate gives the message substance; the floral association can sit beside it without carrying the whole conversation.
FAQ
Must a thank-you bouquet include agrimony?
No. The reference is optional, and an available flower with a sincere note can serve the purpose.
Source
Kate Greenaway: Language of Flowers, plant-to-meaning entries