mel turner wrote:
"a_plutonium" wrote in message
ups.com...
Last week I encountered a patch of stinging nettle and had my hand
irritated for some hours.

Ouch!

For those
unaware of stinging nettle, it is a plant with needles on its stem and
tipped with acid so as the
hand or legs brush against this nettle, the skin is irritated.

Not exactly. The hairs are actually like stiff little hypodermic
needles with glassy walls and a tip that neatly snaps off on contact
so that the hair's contents are injected into the tiny wound the
hair makes.

I have a question on stinging-nettle. What animal caused the evolution
of this stinging plant? Is it grazing animal
such as rabbits or some hoofed grazer?

Why not both, or potentially plant-damaging animals in general? The
tiny needles with painful nerve-stimulating juice inside might work
just as well on almost any animals. This article suggests that the
stinging hairs defend against mammals but not insects:

http://www.jstor.org/view/00301299/ap060198/06a00120/0

I tend to think stinging nettle
evolved because of the prescence
of humans? I wonder if stinging nettle is due solely to the prescence
of humans?

Why humans? There seems to be no reason to think the nettle's stinging
hairs have evolved in any specific relationship with humans. There are
plenty of other animals out there to be stung.

That planet Earth would
not have stinging nettle if not for humanity. And whether there are
biological firsts for stinging-nettle and
Homo sapiens.

Question: is that true?

Again, why think it has anything specific to do with humans?

Second question: If true then how old is this
co-evolving relationship?

The stinging-hairs type of defense has evolved independently in
several different groups of plants. Even in true nettles [family
Urticaceae] there are numerous stinging species in several genera
as well as many non-stinging genera.

http://en.wikipedia.org/wiki/Urtica
http://en.wikipedia.org/wiki/Stinging_nettles
http://en.wikipedia.org/wiki/Dendrocnide
http://en.wikipedia.org/wiki/Dendrocnide_moroides

Besides "true" nettles, there are similarly very nettle-like stinging
plants in the Euphorbiaceae [e.g., Tragia, Cnidosculus] the Loasaceae,
and perhaps some other families.
e.g:
http://waynesword.palomar.edu/wigandia.htm

Many other plants have other sorts of irritating hairs that likely
also play a defensive role.

Some of these adaptations are undoubtedly fairly old [in true nettles,
cladistic analyses may tell us whether stinging hairs would have been
present in the last common ancestor of all modern stinging Urticaceae].

One neat thing worth pointing out is that nettles and similar plants
are genuine examples of _venomous_, not merely poisonous, plants.

cheers

Thanks for the long and detailed discussion. I am wondering how far
back
the stinging nettle lines go in history. Whether they existed before
humanity
existed.

I noticed the cat eating some nettle in springtime, unless I have it
confused
with wild mint. So maybe cats enjoy the nettle acid tipped needles.

I notice my horse, donkey and Llama refuse to eat nettle. Even when I
try
to place nettle before an apple where they refuse to bite into the
nettle. Maybe
the donkey ate some nettle, not sure of that fact?

What I am guessing from my potato patch next to a cucumber patch where
the grasshoppers mowed down the potato leaves but left the cucumber
untouched.

I am guessing that stinging nettle co-evolved with grasshoppers. And
the nettle is
targeting grasshoppers. But I would need some understanding as to how
nettle
hyperdermic needles penetrate a grasshopper or ward off grasshoppers.

The positioning of the needles appears to be a position targeting
grasshoppers.

But grasshoppers mostly have a hard crusted body so how would the acid
of the
nettle play into the grasshoppers body?

Is the age of the nettle classes about the same in historic time--
hundreds of million
of years as the age of grasshoppers? So is there some geological time
age of nettles
that closely follows the time age of grasshoppers?

Obviously if nettles go back hundreds of million years then human
species was not
the evolutionary impetus, but if grasshoppers follow a similar time-
line, then it is grasshoppers
that are the intended victims for stinging nettle.

What I am trying to do is find out the "intended victims" for stinging
nettle.

Archimedes Plutonium
www.iw.net/~a_plutonium
whole entire Universe is just one big atom
where dots of the electron-dot-cloud are galaxies