Tradescantia pallida
Though sometimes accounted a weed, spiderwort is cultivated for borders and also used in containers. Where it appears as a volunteer, it is often welcomed and allowed to stay.
Interesting facts I found on Wikipedia:
The genus takes its name from John Tradescant the elder, an 17th century English plant collector and nurseryman.
The cells of the stamen hairs of some Tradescantia are colored blue, but when exposed to sources of ionizing radiation such as gamma rays, the cells mutate and change color to pink; they are one of the few tissues known to serve as an effective bioassay for ambient radiation levels.
That is interesting! I did not know that!