Ranunculus presents a mixed case in terms of annual versus perennial condition. Ranunculus plants can function in either mode. Environmental conditions, not species, determines annual vs. perennial status.
Ranunculus encompasses a variety of different plants, and can grow in different types of climates and either as self-propagating wildflowers or as cultivated flowers for sale through floral retailers:
The Montana.plant-life.org website identifies the ranunculus genus as including both annuals and perennials and also encompassing, worldwide, about 400 species.
The distinction with perennial versus annual is not determined by species, according to Jerry Balduan, the operator of Green Valley Growers in San Francisco. Two environmental factors, growing area and growing circumstances, influence the perennial versus annual functioning of ranunculus.
When grown outdoors, climate affects whether ranunculus functions as annual or perennial. In warmer growing areas, such as California, a particular ranunculus plant is likely to grow as a perennial; whereas that same ranunculus plant in a colder location such as New England is likely to function as an annual.
Indoor versus outdoor growing conditions also affects the perennial versus annual status of ranunculus. Thus, even in a colder growing climate, a ranunculus plant grown in a pot for indoor growing can function as a perennial when that specific plant would otherwise in that climate function as an annual.