In article , none writes
Hello,

I'm a complete lay-person, so please forgive me if the answer to my question
is obvious. If I have two very different species of plants and they are
both diploids with the same number of chromosomes, will I be able to
crossbreed them, or are there other determining factors?

Thanks

No.

To deviate slightly, you can often cross related diploids and
tetraploids - the offspring, which are triploids, are sterile (or
apomictic), but are otherwise viable. Also, what matters is not so much
the number of chromosomes, but the number of chromosome arms. (There's
several cases of species with varying numbers of chromosomes, tho' I
don't recall such a plant species.)

There's lots of other determining factors, which run from ecological
isolation to hybrid inviability. By manually crossing plants to bypass
some of the earlier ones, but I'd expect that most wide crosses would
fail due to the pollen grains of the pollen parent failing to grow in
the styles of the seed parent. If you get past that then perhaps the
sperm can't penetrate the egg. And if it does perhaps the resulting
embryo doesn't produce the right signals to cause seed maturation. And
so on.
--
Stewart Robert Hinsley