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  Thorns on Aroids
From: <ju-bo at msn.com> on 2009.02.22 at 13:03:14(19132)
Dear Friends,

I would think that any thoughts or study on the ''prickles/spines'' on aroids would start with the Lasiodeae.
Many genera in this group exibit extreme spines, one has not lived till one has tried to handle or re-pot a plant of Lasia spinosa only to be left with the tips of dozens of thorns inbedded in ones hands and fingers, to later fester and become pustules. 
The genus Cyrtosperma runs a close second, and a specimen of C. macrotum I once had from N. E. Papua-New Guinea was very much like a porcupine to touch, and impossible to handle without resorting to leather gloves.  All the other species in this genus that I can think of are spiney!
Podolasia is no better, this genus produces a bloom where even the stipe (the structure below the spadix which attaches the spadix to the spathe/peduncle) is also spiney!   Of interest, the spines on Podolasia all point upwards, while those on Cyrtosperma all point downwards.
The exception is the African genus Lasimorpha, its many spines, which run in parallel rows along its petioles, are sort of ''crystaline'', and somewhat ''blunt'', so handling has not been a problem for me.
A few of the Old World genera are not spiney, the Indian Anaphyllum, and the Asian Pycnospatha have at best ''rough'' petioles.
The Neotropicis have been kind to us with their Lasioid genera, Anaphyllopsis, Dracontioides, Urospatha all are spineless (though there are a couple (?) of species (?) of Urospatha in Fr. Guyana with ''roughish'' petioles), while the genus Dracontium is interesting in that certain species, the petioles demonstrate structures which look like spines, but are generally soft and not ''dangerously'' sharp!
I don`t know the origin of these spines in Aroids, but they must be a good form of defense against browsers and even perching birds, etc.
I hope this assists our friend Dmitry in his research.

Good Growing,

Julius
WPB,  Florida

> From: phymatarum@googlemail.com

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From: "Marek Argent" <abri1973 at wp.pl> on 2009.02.23 at 17:29:14(19135)
Hello Julius,

My Pycnospatha arietina (a juvenille plant) had a few thorns/prickles/spines on its petiole last year:

http://www.wschowa.com/abrimaal/araceum/pycnospatha/arietina.htm

And also my unidentified Anchomanes also has a spiny petiole:

http://www.wschowa.com/abrimaal/araceum/unid/abrianch1.htm

Best,

Marek

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From: "Elizabeth Campbell" <desinadora at mail2designer.com> on 2009.02.24 at 00:31:52(19138)
Dear All:

Here's my two cents - a whole lot more plants than just the Aroids have
thorns in our neotropical forests here in Ecuador, and usually it's to
defend themselves from other plants. The spines on many of the other
plants and trees are there to discourage competition from growing over
them - for example, Ceiba pentandra has spines until about its 100th
year to discourage colonisation by Philodendrons! (They're often the
only smoothly empty plants in the forest, which makes them very easy to
spot....) So any of the free-standing or vining aroids with spines may
have them for the same reason - so as not to be overgrown by other
ferns, orchids, or lianas. For directional spines, I'd look at the size
of the plant and its relative habit - downward pointing ones would tend
to me to indicate that the plant is trying to protect itself from
invadors coming from below, while upward-pointing ones say "don't step
on me."

Lasia is an aquatic, as I understand it. I'd bet the spines are
particularly sharp to dissuade wading birds and crocodilids from
disturbing the mat, as well as to discourage anything that thinks it
looks like a tasty snack.... It would probably only take one nasty
festering thorn wound to keep me away from a plant like that! Then
again, I grow a number of plants that do this to me on a regular basis,
so maybe I'm not as smart as a heron!

Beth

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From: <ju-bo at msn.com> on 2009.02.27 at 10:22:40(19143)
Dear Beth and All

Great idea Beth! Lots more research is needed by folks in the field like you Miss Beth to observe exactly WHY for example climbing Aro ids don`t manage to ''stick'' themselves to the spiny trunk of a Ceiba tree . Could it be additional factors beside just the spines like rapidly pe eling bark as the trunk of the tree expands which may discourage root attac hment?
By the way thanks to Marek for reminding us of the sppines on Anchomanes (and this brings to mind Pseudohydrosme a close (?) relative).
We must also keep in mind the not-so-old but now extinct Magafauna (thro ugh man`s hunting?) and maybe other medium-to-small sized animals which until fairly recently existed through the Neotropics (and further North int o N. America). These animals evolved together with the plants (which stil l exist) so we really need to try to learn and understand what roles the se now-extinct animals played in the evoloution of the defense mech. AND th e distribution of fruit and seeds of these still existing plants.
Just yesterday I was reading about certain trees and plants on New Zealand which are today rare and growing rarer the thoughts are that the now-ext inct giant Ostrich-like birds the Moas used to be responsible for the di stribution of the seeds. When man came to these Islands the Moas were rapidly hunted to extinction together with a man-sized (!!) Falcon-li ke bird the Moas only natural enemy. No more Moas (and no more Falcon-l ike-bird!) LOTS of people so no more seed distribution no more tre es.

Good Growing

Julius

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From: "Elizabeth Campbell" <desinadora at mail2designer.com> on 2009.03.02 at 17:14:50(19151)
Leland, I wonder if there's a chemical that the Ceiba thorns exude that make it inhospitable to plants - it's not just Aroids that won't grow on them when they've got the thorns, they're completely free of competing species. Not even moss or lichen will grow on that bark! It's not particularly delicate or easy-sloughing either, just very very smooth over the thorn surface. Here at least, the thorns comprise the entire bark surface for the first 100 years or so of the tree's life. After that, it becomes a veritable epiphyte condominium, although the tree continues to produce some substance that inhibits the growth of strangler figs. I'd be interested to find out, but I have no clue how to go about testing for an unknown tree phytotoxin. It's not obvious, the way that it is for walnuts - although oddly enough, a slightly thorny Anthurium does tend to colonize these with no ill effects, even though the walnuts are suppressing all other plant growth in the area. I'm at a l oss to explain that one.

Beth

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From: <ju-bo at msn.com> on 2009.03.05 at 11:08:22(19155)
Dear Beth and Friends,

These Silk Cotton trees may be exibiting a condition (whose name I can not recall at this moment!) where some species of tree exude ''something'' which prevents to growth of competing vines, etc.  Here in Florida nothing will grow under the branches/drip- line OR climb a  Norfolk Pine, and I believe Australian ''pines'' and even  native Floridan pines demonstrate this "ability"!
Perhaps someone ''out there'' has additional information on this one?

Good Growing,

Julius

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From: brian lee <lbmkjm at yahoo.com> on 2009.03.05 at 22:56:20(19157)
Dear Beth, Julius, and all,

Aloha.

What you are describing is allelopathy and allelochemicals or alleopathic compounds. I do not know the specifics on Ceiba, but this may be happening on the younger trees and modifies in the mature giants. Normally allopathy involves the roots, but there is nothing to prevent the release of these biochemicals on the stems and leaves.

Aloha,

Leland

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