They are invariably annual and reproduction is by seed alone, which can in many species lie dormant for years in the soil until brought to the surface during cultivation. They have fast reproduction cycles, usually in one year from seed to seed, though some species can have more than one generation in one season. A few species such as groundsel (Senecio vulgaris), shepherd's purse (Capsella bursa-pastoris), red deadnettle (Lamium purpureum) and chickweed (Stellaria media) can survive unharmed through very cold weather and are often able to seed even in winter.