英語の後に日本語が続きます。
They're spiderworts (Tradescantia). The beautiful color contrast between the petals and stamens caught my eye, which is understandable. Purple and yellow are complementary colors, creating the strongest contrast.
Spiderworts are native to North America, one of many plants coming to Japan from western countries at the beginning of the Meiji era (1868 to 1912). The purple of these spiderworts seems paler than last year but they may change color during the flowering period from May to October.
