Now in Japan, we have considerable excitant in pollinosis on hand: the pollen of Japanese cedar, Japanese birch, Japanese alder, Japanese oak, grasses (timothy, orchard, june, rye grass and so on which were introduced, rice, eulalia, chikarashiba-Pennisetum japonica etc), native sagebrushes, Japanese hop and Ragweed.
The most important plant is the cedar which distributes allmost of all in Japan. Its pollen has a antigenically cross reactivity to that of hinoki (Chamaecyparis obusta), sawara (Chamaecyparis pisifera) and mountain cedar. Hinoki and sawara are commonly found as well as sugi (Japanese ceder) in Japan.
The next harmfull plant is sagebrushes. There are so many species among the Artemisiae, but yomogi (Artemisia princeps) and Yamayomogi (Artemisia montana) are of the most importance. Ragweed is not always important, though it is found in some districts except for the northern part of Japan. Ragweed-sensitive patient, however, is increasingly observed for the past several years.
Grass pollinosis patient is not so freqently seen at the middle and southern Japan except for the northern. The early summer grass pollinosis is mainly due to the introduced grasses. The native grasses which contribute their pollen sometimes to the cause of pollinosis in the late summer are rice, eulalia, chikarashiba and so on.
Japanese oak, birch, alder and hop contribute, to a certain extent, to the production of pollinosis. Oak and alder are found on the hills and the small mountains throughout most of Japan. Birch is commonly found at the northern district. Hop grows on a damp ground in the late summer season.
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