Abstract
The weed flora in Tokachi district, Hokkaido, was surveyed at 1967 to 1974. It consisted of 415 species of 67 families, including the poisonous weeds and the naturalized weeds grown in non-arable lands.
These species were classified in the following three groups according to growing places: the upland weeds which are found in and around upland fields (96 annuals and 141 perennials-a total of 237 species of 43 families), the lowland weeds which are found in and around lowland fields (29 annuals and 51 perennials-a total of 80 species of 30 families) and the common weeds which grows both in upland fields and lowland fields (12 annuals and 21 perennials-a total of 33 species of 12 families).
76 species of weeds belonging to 32 families were identified as poisonous. These weeds included 17 annuals and 59 perennials, and 40 species of them were found in only non-arable lands.
119 species of the naturalized weeds were found in arable or non-arable lands. They consisted of 57 annuals and 62 perennials, belonging to 23 families, and 88 species among them were growing in upland fields.
By their weedy members alone, the following families most plentifully represented are: Compositae (59), Gramineae (58), Polygonaceae (29), . Cruciferae (21), Caryophyllaceae (20), Cyperaceae (18), Leguminosae (17), and Ranunculaceae (17).
