The biggest rothschildianum flower mentioned to me by a collector was 45 cm. and that man never lied to me. Tenom had a 42 cm that died a decade ago too.
We can find a few reports in the Orchid Review of 45cm from a massive clump whose owner was Baron de Rothschild ( the french brother...).
The biggest ones I have got and seen are 40 cm. Raymond is another candidate for the 40cm race when grown into a clump, but so far I did not know if it was alive anywhere... It was from the very last batch collected by Azadehdel before he got into trouble in England. According to his owner ( whose first name was Raymond), he got the 5 plants, same size, then one started to grow like hell, big leaves, big flowers. He made a clump out of it, then died of and AIDS related condition. Afterwards, all of his plants went to... well no one knows at all. This photo most likely is the first plant I see reappearing of it...
There is one 40 cm, from Mt Millais x Val ( NOT Val x Mt Millais...) called ' Tarentula' at the Tokyo Orchids Nursery. And I have seen Mt Millais at 36cm. I think it is a culture matter too. Note on the photo that the plant is very dark green, not yellowish like the American or Japanese grow their plants. In Europe we use a lot of urea and ammonium based fertilizer.
Franz Glanz as well has many multiflorals, and use only a Peters, that is only urea-nitrogen based. Same dark green leaves, and big flowers... Peter Schmidt/L'Amazone is one old school grower, and I am sure he uses the same style of fertilizer, urea/ammonium, and little to no nitrate.
