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Wednesday, November 26, 2008

1 m Dawsonia; highest & deepest

Subject: Re: BRYONET: World's most extreme bryophyte (in terms of size)
Date: Wed, 26 Nov 2008 21:22:13 -0000
From: Sean Edwards <sean.r.edwards@btinternet.com>

BRYONET

This interesting topic came up in 2003, and no doubt before. It started
as a highest (altitude) and lowest (depth in water) topic. For those
that haven't access to the archives, here are extracts:

I posted on 5 Mar 2003: "I know that I have read [unsubstantiated?] of
records of Dawsonia superba exceeding 1 m. I have personally measured
it at 850 mm on the Silau Silau Trail, Mt Kinabalu (29 Aug 1995). And
this was just a passing patch, nothing sought out for its height. One of
the things about Dawsonia is that the individual stems are
self-supporting, and although Polytrichum commune can get pretty tall I
doubt that it ever exceeds about 250 mm free-standing."

An extract from the BBS Travelling exhibition (written 1986-7): "Mosses
and liverworts vary in size almost as much as do flowering plants. It is
difficult to say what the biggest moss is, because all of one very large
clump may have grown from one spore. The Giant Haircap Moss Dawsonia
superba, from South East Asia and Australasia, can reach heights of over
a metre. The similar but slightly smaller British moss Polytrichum
commune can form clumps of about 70 cm height, but the individual stems
are not self-supporting. The long flowing stems of the river moss
Fontinalis exceed a metre. The mosses that hang in festoons in tropical
forests are probably longer still."

I have myself measured Polytrichum commune at 700 mm (excluding fruit)
at Lindow Moss and also in Devil's Punch Bowl, UK, agreeing with
Janice's report, but it was in a mound both times.

Gordon Rothero wrote (7 Mar 2003): "I have a stem of Polytrichum commune
from NW Scotland which is 75cm long - part of an extremely large hummock
- but only the final 15cm or so of this will stand erect without
support."

Rune H. qkland wrote (7 March 2003): "Fontinalis antipyretica, which may
abound in small streams (in Norway). It may also reach more than 50 cm,
not in height, but in length, all green."

Guy Brassard wrote (9 March 2003): "Sphagnum also grows very long.
Sphagnum majus in Newfoundland certainly grew to more than 1 m, albeit
in an aquatic habitat (I remember taping one stem to a piece of
cardboard)."

Answering Neil Bell's question about lamellae as a measure of leaf
area, I made a crude calculation many years ago, haven't checked it
since but looks OK, here pasted from lecture notes: "Mosses such as
Polytrichum have developed other mechanisms to control water loss. Along
the surface of each leaf run dozens of ribbon-like lamellae; a small
movement of the leaf will reveal a photosynthetic area about many times
that of the original leaf surface. A simple calculation shows that the
factor increase of surface area is 2X lamella-height in number of
green cells surface area exposed, so for example lamellae five cells
high will have ten times the surface area exposed. If the lamellae are
capped with impermeable cells, then the percentage exposed area goes up
from 0% to 1,000% of a simple leaf without lamellae." Otherwise,
Rhodobryum giganteum would be a contender.

Sean

~~~~~~~~~~~~~~~~~~~~~~~~~

Sean Edwards, Vine Cottage, The Street, Thursley, Surrey GU8 6QF
email: sean.r.edwards(at)btinternet.com
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