It is entirely possible that hybrids of Philodendron xanadu and Philodendron bipinnatifidum exist. I would think that it would be more plausible that the original hybrids occurred in Brazil at Seidel's nursery. I say this as the tissue cultured examples do not shed much pollen until years down the line as the effects of the tissue culture chemicals wear off. That is not to say that someone hasn't done it. I also do not know the influence of the tissue culture on the receptivity of the female flowers...which could be a factor restricting pollination. I have heard of people trying to pollinate Philodendron xanadu, but, I would love to hear if anyone produced viable seeds. To date, I have not heard of this.
There is also a tissue cultured
Philodendron 'Showboat', that is Philodendron xanadu, but a larger selection or one with less of the chemicals influencing dwarfed growth.
There is a large planting of Philodendron xanadu at one of our local hospitals and it blooms regularly. These plants are about half the size of the Philodendron ex: David Woolsey, that grows to the same scale of Philodendron bipinnatifidum. Julius Boos believes that this may be what Philodendron xanadu would look like if not influenced by the tissue culture chemical cocktails.
--- On Mon, 8/24/09, Eric Schmidt <email@example.com>
From: Eric Schmidt <firstname.lastname@example.org>
Subject: Re: [Aroid-l] Aroid-L P. XANADU
To: "Discussion of aroids"
Date: Monday, August 24, 2009, 4:28 AM