I'm not sure it actually exists. There seems to be very wide variations for this species/forma, very little conclusive discussion. There are two photos that make me from two sources (greenish on purple). All the rest look like various forms of cornu-cervi or corningiana/hybrid (I already have both).
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Anon Y Mouse
"Never attribute to malice that which is adequately explained by stupidity." Hanlon’s Razor
I am not being argumentative. I am correcting you!