These are hollyhocks. I was lucky to have a chance to photograph white, pink and red ones at the same time. Hollyhocks are called "tachi aoi" in Japanese, which translates to "standing mallow" and mallows have a special connotation in Japan.
"Mitsuba aoi," which translates to "three leafed mallow," is the crest of the Tokugawa clan, who ruled Japan during the Edo period (1603-1868). This is known nationwide even now because of a long run "samurai" television program about Mitsukuni Tokugawa (1628-1701), one of the grandchildren of Ieyasu Tokugawa, the founder and first shogun of the Tokugawa shogunate of Japan. This period drama was aired initially from 1969 to 2011 and is still rerun now.
In the drama, Mitsukuni travels throughout the country incognito to discover and investigate injustice and in the end defeats and punishes corrupt samurai and merchants. At the end of each episode, Mitsukuni (or more specifically, one of his two samurai retainers) brandishes an "inro" pillbox with the "three leafed mallow" crest to reveal Mitsukuni's identity, i.e., a member of the Tokugawa clan. (By the way, although Mitsukuni existed and was a relation of the shogun, the drama episodes are all fictional.)
Interestingly, however, the Tokugawa clan's crest is not "three leafed mallow" actually but Asarum caulescens Maxim., which is a very plain, two-leafed or heart shaped plant. The Tokugawa clan's crest, three-leafed mallow, is said to be modeled on this plain plant.
Then, another question comes up. Why did someone who wanted to rule the country choose such a plain plant as their crest? One website says that many samurai clans during the age of warring states (1467-1615) chose plain plants as their crests to show that they were strong and hardy enough to survive in such harsh circumstances as these plants were.