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That is a very impressive clump of C. tricarinata, Herman! Mine has more than a few years to go before it looks anything like that.Some of the names are incorrect though, your 'brevicornu' is clearly a brevicornu hybrid, possibly with discolor. It seems that lately, a lot of hybrids are being sold as one of their parent species, which bothers me to no end. C. bicolor is the old name for what is actually the hybrid between C.discolor and C. sieboldii. Having said that; your plant looks exactly like C. discolor from what I can see.Your C. sieboldii is possibly a hybrid lookalike, but I can't say for certain.
Hermann, I am most impressed that you can grow these outside. What kind of soil do you have? ph?