The haploid-diploid cycle manifests itself in ferns
in big diploid sporophytes and small haploid gametophytes

I remember that from high school.

except in some populations hit by the Ice Ages.

What happened to them?
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)

In article ,
[Iris Cohen] wrote...

The haploid-diploid cycle manifests itself in ferns
in big diploid sporophytes and small haploid gametophytes

I remember that from high school.

except in some populations hit by the Ice Ages.

What happened to them?

I think he's thinking of the "Appalachian gametophyte" and/or similar
cases, where populations of vegetatively-reproducing gametophytes that
never produce adult sporophytes range far beyond the known
distributions of closely-related [tropical and subtropical] forms that
do form sporophytes. The best-known example is in the genus Vittaria,
but there are also Hymenophyllaceae and grammitids. The Vittaria and
hymenophyll gametophytes are highly branched, and produce small
gemmae that serve as propagules. [So do the gametophytes of their
relatives with complete life cycles]

http://www.natureserve.org/explorer/...e=VITTARIA+APP
ALACHIANA
http://arnica.csustan.edu/b3100/pterophyta/vittaria.jpg

The ice-age story would suppose that these gametophytes are relics
of formerly widespread warm-climate ferns. e.g.:

http://www.cumberland.sierraclub.org...t/news1201.asp

"Three species of ferns are restricted to the cliff line habitat.
These include the filmy fern, Trichomanes boschianum, a member of a
semitropical genus that is able to tolerate Kentucky winters only by
growing under the protection of overhanging cliffs. Two species of
ferns are found here only in the gametophyte stage, having apparently
lost the ability to produce the familiar sporophyte stage. The
Appalachian gametophyte, Vittaria appalachiana, could easily be
confused with a liverwort at first glance, yet it is a vascular plant
that is almost certainly a relict from ancient times when Kentucky’s
climate was considerably warmer than today’s. The other species that
exists only as a gametophyte is Trichomanes intricatum, a vascular
plant that resembles a clump of green thread."

IMO, it's questionable that these cases need have much to do
with ice ages; why couldn't it instead be a matter of spores of
tropical ferns dispersing to and becoming established in places
far beyond the limits of environments capable of supporting
their sporophyte generation?

cheers

The haploid-diploid cycle manifests itself in ferns in big diploid
sporophytes and small haploid gametophytes
wrote
I remember that from high school.

except in some populations hit by the Ice Ages.
[Iris Cohen] wrote...
What happened to them?

mel turner schreef
I think he's thinking of the "Appalachian gametophyte" and/or similar
cases, where populations of vegetatively-reproducing gametophytes that
never produce adult sporophytes range far beyond the known
distributions of closely-related [tropical and subtropical] forms that
do form sporophytes. The best-known example is in the genus Vittaria,
but there are also Hymenophyllaceae and grammitids. The Vittaria and
hymenophyll gametophytes are highly branched, and produce small
gemmae that serve as propagules. [So do the gametophytes of their
relatives with complete life cycles]


http://www.natureserve.org/explorer/...Name=VITTARIA+
APPALACHIANA
http://arnica.csustan.edu/b3100/pterophyta/vittaria.jpg

The ice-age story would suppose that these gametophytes are relics
of formerly widespread warm-climate ferns. e.g.:

http://www.cumberland.sierraclub.org...t/news1201.asp

"Three species of ferns are restricted to the cliff line habitat.
These include the filmy fern, Trichomanes boschianum, a member of a
semitropical genus that is able to tolerate Kentucky winters only by
growing under the protection of overhanging cliffs. Two species of
ferns are found here only in the gametophyte stage, having apparently
lost the ability to produce the familiar sporophyte stage. The
Appalachian gametophyte, Vittaria appalachiana, could easily be
confused with a liverwort at first glance, yet it is a vascular plant
that is almost certainly a relict from ancient times when Kentucky's
climate was considerably warmer than today's. The other species that
exists only as a gametophyte is Trichomanes intricatum, a vascular
plant that resembles a clump of green thread."

IMO, it's questionable that these cases need have much to do
with ice ages; why couldn't it instead be a matter of spores of
tropical ferns dispersing to and becoming established in places
far beyond the limits of environments capable of supporting
their sporophyte generation?

cheers

+ + +
Something like that. The story, as I remember it being published, is of
several species that had gametophyte-only populations, both in North-America
and Europe. IIRC these were not tropical ferns but local ferns and the Ice
Ages were definitely drawn into the story. It was a few years ago and I did
not read all that closely, but that is how I remember it.

I never looked further into the matter, having no interest in ferns. A quick
look on the web shows a case in the UK:
http://www.english-nature.org.uk/tex...rare_ferns.asp

PvR