Houstonia caerulea – also known as bluet, innocence and Quaker-ladies.
Despite being tiny (1 cm across), these are charming showy flowers with incandescent pale blue flowers with tinged with yellow at the center that light up the ground just before spring as the daffodils are breaking out of the ground. The flowers are four-lobed and the stems may grow up to 20 cm tall with one flower per stalk.
The plant has spatulate to lanceolate and opposite leaves. The foliage is a basal rosette. The plant blooms from March to June. The plant spreads by the underground rhizomes. It thrives in moist acidic sandy loamy soils in shady areas, growing especially well among grasses in open woods or glades.
Bluet is a perennial herb belonging to the Rubiaceae (Madder family). It is native to North America but has naturalized in Japan. This herb was introduced as a garden plant into Japan in the final days of Showa Era.
Bluets may be difficult to get established. They need lean soil and to be free from competition by other plants. They tend to be short-lived and can disappear in dry weather only to reappear next spring. As long as they get regular water, they stay up and are visible. But once established, they self-sow and show up in cheerful colonies popping up in unlikely places.