Facultative biennials are plants that have the potential to flower in their second or a later year of life (typically 3, 4, or 5), whereas obligate biennials always flower in their second year of life (Kelly 1985, Klinkhamer et al. 1987a, Klinkhamer and de Jong 1988). This difference is explained in many facultative biennials by the fact that their rosettes (Juveniles) must reach a certain minimum size, depending on the species, population, and individual, before they can be vernalized and bolt (produce a flower stalk) (Werner 1975, Baskin and Baskin 1979a, van der Meijden and van der Waals-Kooi 1979, Gross and Werner 1983, Klemow and Raynal 1985, Lacey 1986, Wesselingh and Klinkhamer 1996, Reekie et al. 1997), whereas those of obligate biennials do not have this requirement-i.e., even seedlings or small juveniles can be vernalized (Baskin and Baskin 1984). Thus, many so-called biennials do not, in fact, flower in their second year because they do not reach the critical size for vernalization during their first growing season. In both facultative and obligate biennials, the entire plant dies after it reproduces once; the plants are monocarpic (semelparous).