Ecological life cycle of Chaerophyllum procumbens variety shortii (Apiacheae), a winter annual of the North American dedicuous forest
Numerous winter annuals occur in temperate eastern North America. Based on life cycle information and flowering period, the flora of northeastern USA and adjacent Canada described in Gray's Manual of Botany (Fernald 1950) contains 96 winter annuals (C. Baskin unpublished). This list includes native and introduced species in 57 genera and 23 families. The majority of these winter annuals grow in open, well-lighted habitats such as fields, lawns, waste places, and rock outcrops, and only a few, including Chaerophyllum procumbens (L.) Crantz, Collinsia verna Nutt., Corydalis ftava (Raf.) DC., Nemophila aphylla (L.) Grumrn., and Phacelia ranunculacea (Nutt.) Const. are found in mesic deciduous forests.