----- Original Message -----
> Do you know any wild plants who started to split their chromosoms .?

I googled, using different search terms such as paleopolyploids, "ancient
polyploids,"  "natural polyploid,"  polyploid + wheat, polyploid + fruit,
etc.  Play around with different combinations, and you'll surely find a lot
to read.
 :-o

But to answer your question as directly as I can, below are a few things I
found.

Theola
___________________________________

http://www.tarweed.com/pgr/PGR00-011.html
"Tetraploid wheats were established by 10000-8000 BC. T. dicoccum was
probably the first cultivated wheat, but may have arisen in the wild and
become established as a result of the artificial selection of naturally
occurring stands of wild wheat."

http://fletcher.ces.state.nc.us/programs/nursery/metria/metria11/ranney/poly
ploidy.htm
Polyploidy can naturally arise in a number of different ways.
..........
Role of polyploids in plant evolution.
In contrast to the gradual evolutionary process whereby new species evolve
from isolated populations, new species of plants can also arise abruptly.
The most common mechanism for abrupt speciation is through the formation of
natural polyploids. Once a tetraploid arises in a population, it can
generally hybridize with other tetraploids. However, these tetraploids are
reproductively isolated from their parental species. Tetraploids that cross
with diploids of the parental species will result in triploids that are
typically sterile. This phenomenon provides a "reproductive barrier" between
the polyploids and the parental species - a driving force for speciation.
........
One question that frequently arises is whether or not polyploids inherently
have greater stress tolerance. For example, it has often been observed that
disproportionate number of polyploids are found in cold, dry regions. Some
argue that this is a spurious correlation (Sanford, 1983) or possibly the
result of intermixing of species and formation of allopolyploids during
glacial periods (Stebbins, 1984). However, polyploids may also have certain
characteristics that do provide some adaptive benefits. Molecular studies
have demonstrated that allopolyploids exhibit "enzyme multiplicity" (Soltis
and Soltis, 1993). Since allopolyploids represent a fusion of two distinctly
different genomes, these polyploids can potentially produce all of the
enzymes produced by each parent as well as new hybrid enzymes. This enzyme
multiplicity may provide polyploids with greater biochemical flexibility;
possibly extending the range of environments in which the plant can grow
(Roose and Gottlieb, 1976).

Interesting article about apples:
http://peacecorps.mtu.edu/povel/Eng_the_apple.htm

Like cats and people, most apple trees are diploid--that is, their genes
occur on pairs of chromosomes. Typically, apples have seventeen  pairs of
chromosomes, for a total of thirty-four. But some varieties are haploid,
with seventeen single chromosomes. Others, especially among  crab apples,
are polyploid, which means that their chromosomes are not paired but
tripled, quadrupled, quintupled, or even wadded up into  bundles of six. In
fact, some apples have as many as eighty-five chromosomes. And each of the
genes on each of the chromosomes can have different alleles (alternative
forms). A single seed may thus contain a lot of genetic variation that has
accumulated down through the ancestral lines.

Orchardists have unquestionably benefited from the apple's easygoing
acceptance of extra chromosomes. Many familiar varieties of apples
are polyploid: Stayman, Jonagold, Baldwin, and the beloved old pie apple
Rhode Island Greening. The Jonagold is a modern, contrived cross
between Jonathan and Golden Delicious parents. But the Stayman sprang up all
on its own, from a Winesap seedling in Kansas; the Baldwin
and Rhode Island Greening, too, were spontaneous polyploids.