Japanese knotweed; flowering bamboo
A common perennial plant (Reynoutria japonica) found across Japan; young shoots are edible and it is sometimes used in traditional medicine.
In spring, you can pick and eat the young shoots of Japanese knotweed.
The origin of the name イタドリ is uncertain; it may be related to the plant's traditional use for treating pain (痛み取り), but this is not confirmed.