My semps are mostly small to middle sized. My biggest one until now used to have about 8" before it flowered recently. My current biggest one is about 5" in diameter, but I saw its mother at about 12" diameter, when I received the 2" chick in May from a local nursery. They told me they once received it under the name 'giganteum ...or something else that means big". A NOID I would say.
