Re: Thorns on Aroids
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!
Date: Sun, 22 Feb 2009 13:03:14 +0000
Subject: [Aroid-l] Thorns on Aroids
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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.
> From: firstname.lastname@example.org
> To: email@example.com
> Date: Fri, 20 Feb 2009 14:36:19 +0800
> Subject: Re: [Aroid-l] Thorns at anubiases
> Dear Dmitry,
> As I mentioned in my last email, we are really not all aware of what role
> such prickles might play in the aroids. As Tom has also mentioned they occur
> in Neotropical Homalomena too. The definition of a thorn is an indeterminate
> structure (such as a stem or root) capable of lateral growth through
> branching (and even of flowering and bearing leaves in some instances, that
> have a protective role. Thorns are most commonly found in Rosaceae (e.g.,
> Crataegus), Fabaceae (notably Gleditschia) and Rhamnaceae (many genera).
> Very best
> ----- Original Message -----
> From: <firstname.lastname@example.org>
> To: <email@example.com>
> Sent: Wednesday, February 18, 2009 8:19 PM
> Subject: Re: [Aroid-l] Thorns at anubiases
> > Dear Peter,
> > This error in terms is probably caused by features of transfer between
> > Russian and English. In Russian such epidermal outgrowths are called as
> > thorns. Indeed, I found in the literature that J. Bogner named them as
> > prickles, but he does not write about their role. I have only few
> > knowledge about others Aroids. Therefore, could You tell me about a role
> > of such prickles in Anubias?
> > Best regards,
> > Dmitry Loginov
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