O. umbellatum is more widely sold. I checked mine from when I first had it in a pot in 2010, there wasn't many leaves showing but they do look strong. I blew the ID photo up, the flower form looks correct as well as the branching and green backs to the petals.
In 2012 in a flower bed. some leaves are visible which look to be dying back, this was on 14th May but I haven't seen them flowering yet this year, I haven't seen leaves growing either so they might have 'disappeared'.
