What are groups of plants or animals with similar traits of any rank called?

The correct option is taxon.

Let us break down the classification of living organisms to understand why taxon is the correct term:
1. Taxonomy is the branch of science concerned with classification, especially of organisms. In biological classification, organisms are grouped based on shared characteristics or similar traits.
2. A taxon (plural: taxa) is defined as a taxonomic group of any rank, such as a species, family, genus, order, class, phylum, or kingdom. It represents a concrete biological object or group of objects that are classified together because they share similar traits.
3. The other options represent specific ranks within the taxonomic hierarchy:
- Genus: A specific rank below family and above species, grouping closely related species.
- Species: The most basic unit of classification, representing individual organisms that can interbreed.
- Order: A rank below class and above family.
Since the question asks for a group of plants or animals with similar traits of any rank, the general term taxon is the correct answer.