Tetraploid Hostas
Very
simply, a tetraploid plant has four sets of chromosomes rather than
two. This can occur naturally, rarely, or can be induced chemically.
Diploids, with two sets of chromosomes, are the norm. In hostas, as far
as I know, only H. ventricosa is a naturally occurring tetraploid
species. Induced tetraploids are very common in the daylily world, but
are a fairly recent development in hostas. 'Patriot', and 'Grand
Tiara', two of the earliest and best known, were both registered in
1991, but only fairly recently has there been a concerted effort to
convert a large number of popular diploid hostas.
Certain
herbicides, such as Surflan, are known to occasionally induce
tetraploidy, and presumably the earliest conversions were accidental
byproducts of herbicide use. Recently, breeders, hobbyists, and
especially tissue culture labs have been using chemicals to try to
produce them intentionally, and the availability of converted plants has
been increasing rapidly.
Tetraploid
hostas generally have thicker leaves, more pronounced variegation,
darker color, larger flowers on thicker scapes, and because the leaves
and leaf petioles are thicker and stiffer, the form of the plant may be
more upright. Because the leaves are thicker, it also seems logical that
they may be more resistant to slugs and other causes of leaf damage.
I think
that one of the most important benefits shows up in the white-centered
hostas, where the tetraploid forms are often less likely to burn and
melt out in the centers. An example is 'Island Charm' which I stopped
growing some time ago because it didn't hold up well for me. It's
tetraploid form, 'Fantasy Island' is an excellent grower here, and may
be the best small, white-centered hosta I've grown. Another example is
'American Sweetheart', which has a much thicker, more durable leaf
