From the Kumamoto International Botany Desk (merged with the Things Unlikely to be Food but Are Desk due to overlap): Petasites japonicus (in Japanese, fuki - as is common with botany, choose your kanji: 蕗、苳、款冬、菜蕗) is a ground-covering plant with an extensive root system which emits buds at about this time of year. The plant has evolved such that the buds, known as “fukinotou,” are highly astringent (bitter) to prevent them from being eaten, but the plant during its evolution had apparently never considered the Japanese housewife.
Soaked in water for a day and then tempurad the hell out of, the result is a pleasingly, mildly bitter taste that goes well accompanied by grated daikon, salt, or tenyuu (天ゆう, a type of sauce often used with tempura).
Below is a photo of a plate my wife recently tempurad the hell out of, a photo of a bud, and a link to a Wikipedia page. Look around your neighborhood and you can probably find them. Then all you need is a Japanese wife. - William