In Kate Greenaway's Language of Flowers, the entry for Amaranth (Globe) reads: Immortality. Unfading love.
A lasting sentiment in words
The globe-amaranth entry combines permanence with affection. Those are symbolic ideas assigned by the dictionary, not a statement that a relationship or a flower will literally last forever. Retain globe in the name rather than merging it with other amaranth entries.
For an anniversary or remembrance note, the useful part is the intention to remember and care. Put that intention into your own words. Avoid turning the entry into a claim that this flower belongs to one ceremony or tradition everywhere.
FAQ
Does the symbolism guarantee lasting love?
No. It describes a sentiment, not an outcome or a test of a relationship.
Source
Kate Greenaway: Language of Flowers, plant-to-meaning entries