Studies of the Kinds of the Weeds of Arable Land in Japan and Their Geographical Distributions : VI. The origin and history of Japanese weeds

Abstract

In this study about the weeds on arable lahd in Japan, the following five groups were suggested from their present geographical range, though it must be admitted that we cannot show their origin exactly. The historical consideration has also been given in this paper. 1) The recently naturalized plants have been introduced in recent year. 2) The old naturalized plants were introduced from Europe or Eurasia through China in the early stage of history. 3) Cosmopolitan. 4) The prehistoric naturalized plants were introduced from Central and South China in ancient times. 5) Native species. 1) The recently naturalized weeds on upland field : 27 species were originated from Europe, and some of the most important are as follows; Senecio vulgaris, Veronica arvensis, Cerastium visosum, Rumex Acetosella, Festuca Myuros, etc.; 5 from Eurasia, Veronica persica, etc.; 9 from Nouth America, Erigeron annuus, E. canadensis, Euphorbia supina, Oxalis Martiana, etc.; 6 from New Tropical regions or South America, Oenothera odorata, Amaranthus retroflexus, etc. 2) The old naturarized weeds: 8 species were originated from Europe. Sonchus brachyotis, Vicia sepium, V. tetrasperma, Stellaria neglecta. Polygonum nodosum, P. Persicaria, Poa annua and Polygonum lapathifolium. All these species are upland field weeds, except the latter one which is paddy field weeds. 25 species were originated from Eurasia, among them Galium spurium, Elsholtzia patrini, Lamium amplexicaule, Capsella Bursa-pastoris, Chenopodium album, etc., are in upland field, whereas the following 13 species are in paddy field, Elatine triandra, Cardamine flexuosa, Ranunculus sceleratus and the others. 3) The species of old world origin or Cosmopolitan; 27 species on upland are Stellaria aquatica, Bulbosylis barbata, Digitaris adscendens, Equisetum arvense, 0xalis corniculata, Portulaca oleracea, Amaranthus ascendens, Polygonum aviculare, etc.: 26 are found in paddy field, among them there are Bidens tripartita, MyrioPhyllum verticillatum, Nasturium palustre, Eleocharis acicularis, Hydrocharis asistica, Ceratophyllum demersum, Najas marina, etc. 4) The prehistoric naturalized species: They are originated from South eastern Asia and especially interesting because these weeds are attendant on rice plants. Among them, Eclipta alba, Dopatorium junceum, Lindernia angustifolia, L. Pyxidaria, Limnophila sesseliflora, Ludwigia prostriat, Rotala indica, Monochoria vaginalis, Eriocaulon sieboltianum, Cyperus diffomis, C. Iria, Fimbristylis miliacea, Echinochloa crus-galli var. oryzicola. etc. are most important. 5) The Japanese native species; there are endemic species and the mutual common species in Japan, Korea, China, or Siberia, etc. The former contains only two species; Pleioblastus spp. and Sagittaria Aginashi. The latter would be perhaps the native species in those days when Japanese archipelago was detached from the continent (the last part of Diluvial epoch or the early years of the Allucual epoch) The native species which can be seen in Eastern as well as Northeastern Asiatic continent are amounted about 130 species on upland field and about 90 on paddy field. The most species, however, are slightly harmuful weeds, i.e., they are grown on the bordering foot-path or in the edge of irrigation ditches. A few species are noxious. As mentioned above, most of the troublesome weeds in Japan were found among the foreign species