Genus and species together constitute the formal scientific (Latin binomial) name for plants and animals. The genus is always capitalized and species is always lowercase. Italicize both genus and species when given together. Italicize the genus when used alone in speaking of the genus; set the genus roman when used generically.
Example: Verticillium dahliae is the cause of Verticillium wilt.
Use the whole scientific name at first use in running text and captions; abbreviate to “Genus sp.” (singular) or “Genus spp.” (plural) in subsequent use.
Example: Carduelis tristis (American goldfinch).