American Weeds in Japan

 

I visited Japan earlier this month and was surprised to spot several of our native plants behaving badly in unmanaged spaces such as along railroad tracks and on the edges of fields. The first one I noticed was mare’s tail (Erigeron canadensis syn. Conyza canadensis), an annual plant that was growing in cracks and untended sidewalk plots near our hotel in Tokyo. It was amusing to see this little weed work its way into the urban environment.

Solidago altissima

Erigeron canadensis

A trip to Mt. Fuji took us by train through rural areas and revealed a far more serious invasive: tall goldenrod (Solidago altissima). The spread of this plant in large groups and across large areas was disturbing (no pun intended). This website explains that it was intentionally brought in as an ornamental and for honeybee support around 1900 and tends to be its most aggressive in untended areas.

Aggressive spread of goldenrod

Other invasive American plants can be found on this list, including giant and common ragweed (Ambrosia), broomsedge (Andropogon), tickseed (Bidens), black locust (Robinia pseudoacacia), pokeweed (Phytolacca americana), and ticktrefoil (Desmodium). I personally saw all these things just in our short visit and limited travels.

Giant ragweed

Pokeweed

I saw other American natives being used deliberately as ornamentals such as black-eyed Susans (Rudbeckia) and scarlet hibiscus (Hibiscus coccineus). A visit to an ornamental garden in the Mt Fuji area found plants like sourwood (Oxydendrum arboreum), oakleaf hydrangea (Hydrangea quercifolia), and muhly grass (Muhlenbergia capillaris).

Other exotic plants that are invasive for us were also invasive for them, of course, but I was also particularly on the lookout for some of their native plants that are invasive to us—kudzu and Japanese knotweed, for example—and I did see them growing rampantly in untended areas, especially along railways. I also was curious about finding their native Jorō spiders and we did, particularly in the more natural areas around Mt Fuji. The webs were big and communal, just like here.

Cryptomeria japonica at
Kitaguchi Hongu Fuji Sengen Shrine 

My trip would not have been complete without admiring some of their beautiful Japanese maples both in gardens and in the wild. 

We also found lots of Japanese cedar (Cryptomeria japonica), both in the wild and at temples and shrines (these enormous trees are sometimes called Japanese Temple Cedars and are quite revered). Azaleas were not blooming but they were frequently used as urban street shrubs, and of course Japanese cherry trees were everywhere (again, not blooming).