This is one of the ‘Spiderworts’, and is a hardy relative of the climbing houseplant commonly known as ‘Tradescantia’.
There are several species and varieties of Spiderwort available for gardens, including the x andersonii group, which are very good garden plants indeed. The x andersonii group are hybrids which are descended from this species, and several others – all native to north America where they dwell in prairies and woodland clearings.
We like this species because of its elegant simplicity. It is a more gracile species, and enjoys growing in a more mixed, informal setting instead of forming a tight clump. Perhaps the only downside is that it is much beloved by Slugs and Snails, but we can hardly hold it, or them, to account.
Height to around 70cm, perhaps more in shadier situations where it would stretch toward the light. Clumps are looser than the andersonii group, but tend not to be too invasive.