Michael,
Unfortunately the ploidies are not obvious although a rule of thumb is that the tetraploids ARE BIGGER than the diploids. However, the tetraploid arachnoideums are really no bigger than the diploid ones. The pollen will be about 1.4X bigger under the microscope, if you have one available to you.
I've only crossed within the eu-Sempervivum and Jovibarba, not between. Mark Smith and others have been successful. I tend to think PAST the F1 so I want fertile plants to continue the line.
Kevin
