Should the infraspecific epithet agree in gender with the genus name?

Question

Let's take the following plant name

Gymnocalycium mihanovichii

So we were to designate the yellow form of the plant, would it be

Gymnocalycium mihanovichii f. aurea

because forma is feminine or

Gymnocalycium mihanovichii f. aureum

because Gymnocalycium is neuter?

Hope the question is on-topic

Answer 1

This is governed by the International Code of Nomenclature for algae, fungi, and plants or by the International Code of Zoological Nomenclature.

For plants, infraspecific names are covered in Article 24. Article 24.2 states:

Infraspecific epithets are formed like specific epithets and, when adjectival in form and not used as nouns, they agree grammatically with the generic name (see Art. 23.5 and 32.2).

Article 23.5 reads:

The specific epithet, when adjectival in form and not used as a noun, agrees with the gender of the generic name; when the epithet is a noun in apposition or a genitive noun, it retains its own gender and termination irrespective of the gender of the generic name. Epithets not conforming to this rule are to be corrected (see Art. 32.2) to the proper form of the termination (Latin or transcribed Greek) of the original author(s). In particular, the usage of the word element ‑cola as an adjective is a correctable error.

Article 32.2 states that names are still validly published, even if their terminations are incorrect.

In this case, since "aureum" is an adjective, it should agree with the genus name.