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Re: EVOLUTION OF HOSTAS

  • Subject: Re: EVOLUTION OF HOSTAS
  • From: "W. George Schmid" <hostahill@Bellsouth.net>
  • Date: Wed, 1 Sep 2004 19:09:04 -0400

Chick
There is no fossil evidence as of now.

Cytologists found Hosta to be karyotypically similar to Yucca, Agave,
Camassia and other genera so, principally on cytological grounds, it was
proposed to include Hosta with the Agavaceae and evidence for this and
similar placements was provided by a number of researchers. Embryological
information based on serology found support among cytologists, but because
karyotypical similarities appear to be common among plants formerly placed
in the Liliaceae, however placements based on cytological evidence alone are
no longer considered conclusive.

Analysis of the divergent morphologies of the original populations in Japan,
Korea and China reveals that Japan is not the evolutionary birthplace of the
genus, since the native Japanese species are morphologically quite uniform
when regarded in a broad sense. Palynological (pollen) evidence indicates
that the progenitor of Hosta may have been lily-type ancestors from which H.
plantaginea evolved and an evolutionary trend can be seen in the developing
pollen types from reticulate through rugulate or rugulate-baculate to
rugulate-granulate type. I believe this trend is also seen in the
variability of macromorphological characters when correlated to geographic
location and environment.

Predecessors of the genus probably migrated from the east-central Chinese
mainland, where the most ``primitive'' hosta still exists (H. plantaginea),
through southern Manchuria into the Korean peninsula and via this southern
route to southern Japan. The northern route extended along the coast of the
south-eastern USSR following a path on the southern side of the Sikhote-Alin
mountain range and migrating to Sakhalin and from there south into Hokkaido
and Honshu. The main Japanese islands providing a climatologically and
ecologically very diverse habitat gave rise to increased speciation. I
believe that the taxa growing in northern Kyushu (H. tibai), on Tsushima
Island (H. tsushimensis) and the southernmost islands of Korea (H. jonesii)
may have originated with the northern branch of evolution, while all other,
highly differentiated Korean taxa originated with the southern evolutionary
branch after becoming geographically isolated in insular Korea and it was
only through geographic isolation that these species remained distinct.

On the main Japanese islands natural, proximal populations probably have
been hybridizing and intergrading for centuries. Hybridization is usually
assumed to take place between completely divergent species but this may not
be totally correct because it assumes that the two hybridizing stocks are
composed of individuals which have gone through past complete divergence,
i.e. they evolved over centuries with the attendant production of a
reproductive barrier. The Chinese night-blooming H. plantaginea and
day-blooming Japanese and Korean species are reproductively isolated from
each other morphologically, this barrier can be easily overcome by human
intervention.

Phylogenetically, close affinity with Agave, Camassia, Hemerocallis,
Hesperocallis, Leucocrinum, Manfreda and Yucca have been suggested which has
created rather numerous phylogenetic placements, each one having its
proponents so there is no real agreement on the phylogeny of Hosta.

H. venusta, for example is less than 15,000 years old. The propagules of H.
venusta were moved from southeastern Korea to Cheju Island after the last
ice age. The geological age of Cheju Island is estimated to be 13,000 years
so H. venusta found only on this island must have speciated after the
volcanic island became habitable. During the process of adapting to a new,
hostile, basaltic island habitat of recent origin, H. venusta underwent
subsequent genetic changes. It was determined that 49 enzyme bands of H.
venusta are a subset of 72 bands found in H. minor so establishing a very
close relationship and making H. minor the starting point for H. venusta.

Since there are no hostas native in North America but many other Asian
species crossed the land bridge it can be assumed that hostas must have
evolved after the Bering land bridge disappeared.

A lot of this is supposition, but there is evidence for many of the
opinions, including mine. George

W. George Schmid
Hosta Hill - Tucker Georgia USA
Zone 7a - 1188 feet AMSL
84-12'-30" West_33-51' North
Outgoing e-mail virus checked by NAV
----- Original Message -----
From: "Chick" <chick@bridgewoodgardens.com>
To: <hosta-open@hort.net>
Sent: Wednesday, September 01, 2004 4:17 PM
Subject: EVOLUTION OF HOSTAS


> I once read, I think in an article by Bob Solberg, that hostas, being
> monocots, are rather primitive plants, evolutionarily speaking.  George
> Schmidt said recently that there is no fossil evidence that the plant is
> very old, again evolutionarily speaking.
>
> Where do hostas come from?
>
> Chick
>
> ---------------------------------------------------------------------
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> message text UNSUBSCRIBE HOSTA-OPEN

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