Apparent radius against mean parallax for the clusters confirmed by Gaia DR2 as of this paper (black dots) as well as the isolated groups (green) and elongated structures belonging to “strings” (cyan crosses) reported by Kounkel & Covey (2019) in the Gaia DR2 data. For the latter data, a proxy for r₅₀ was estimated as . Four dynamically evolved clusters are labelled. The dotted lines indicate the angular size corresponding to 15 and 40 pc.