A singular misstep: correcting "a fungi"

What kind of error is it?

Grammatical error: incorrect use of singular vs. plural form.

Why do people make this mistake?

People often confuse the plural term "fungi" with the singular because many Latin-derived biological terms end in "i", leading to the assumption that they are singular.

What is correct?

The correct singular form is "fungus", while "fungi" is the plural form.