Pretty much, no. There are exceptions, I suppose, but as a whole, I think only plants from the same genra, like rosa or acer, can cross-pollunate. I could be wrong, though. I know with animals that you can't mix a horse and a cat, and plants probably work on the same principal.

There are certain hybrid types of flowers that can go hybrid but for the most part but with enough manmade enhancement we can cross almost anything.

Here is a link that might be useful: Types of flowers

Laridarsarm,

"...with enough manmade enhancement we can cross almost anything."

I agree. The tissue culture technique of somatic cell fusion to produce cytoplasmic hybrids is sometimes referred to as "cybridization". Using somatic hybridization it is possible to create hybrids that would not be recoverable by normal crossings (due to taxonomic or sexual barriers). I am interested in various hybrids involving zinnias.

I think it would be interesting to cross marigolds with zinnias. I know from experience that simple cross-pollination (both ways) does not work. Zinnias have more colors and marigolds have better foliage, so a hybrid could combine the best characteristics of the two, to create a really good ornamental plant.

I am also studying tissue culture as a potential way to asexually propagate many "copies" of any unusually good zinnia hybrid. Such micropropagation can be more effective than conventional cuttings propagation. This zinnia that appeared in my zinnia patch last year is one that I would have micro-propagated if I had perfected the technique at that time.

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I saved seeds from it and have grown several of its progeny from seeds, but so far none has duplicated the form of the parent. My tissue culture experiments have produced only callus tissue, and no shoots. Hopefully this year I will learn to micropropagate zinnias using tissue culture methods.

ZM