Crests are formed when the meristem (growing tip of the plant, in semps it would be the tissue at the center of the rosette) is normally DOME shaped. This allows for a symmetry of the plant as leaf primordia arise from the dome in an orderly position creating a symmetrical rosette. When the meristem expands to a LINE now the leaves arise from points along the line, forming a crest instead of a normal rosette.
Some cultivars are more prone to this. Fuzzy Wuzzy is the champ at this and it's pod parent Denise's Cobweb forms them often too. However I have never seen them on Hot Shot or Devil's Advocate, that are its sister seedlings. Butterbur is a non-cobweb that forms them often too. The one on Dark Cloud last year was 9" across. Just amazing!
The genetics of it is rather poorly understood. It is considered a teratological form. Some consider it is a virus although I have seen no instance where it has been transferred to another cultivar.
Kevin
