Recently, as one does, I was pulling weeds in my garden. I have a bit of a thistle problem this year, and I had to buy a pair of heavy rawhide gloves
to do it. Even with such gloves, it's a task that requires some tenderness...to avoid getting tenderized. <smirk>
And it got me wondering...what substance are thistle spines made of..? Specifically, I'd like to know if they're made of silicon dioxide, also known
as our ancient friend, glass. There are many examples of "bio-glass" in the natural world, such as diatom skeletons, nettle spines, and the thorns of
some cacti.
I googled around for a while, but I couldn't find any information on this topic.
[Edited on 2021-9-13 by spinjector]Tsjerk - 12-9-2021 at 11:48
Woody parts of plants are made of lignin, which usually strengthens cellulose structures over time. I don't know whether there is a lot of lignin in
these spines already, but it is probably a combination of the two.
As far as I know SiO2 forms microstructures mostly in monocotyledons, for example small crystals in the cell walls of grasses to make them harder to
chew for animals without continously growing molars. These structures are usually spread throughout the plant, instead of localized in certain parts
of the plant. SnailsAttack - 12-7-2023 at 20:26
A number of plants accumulate calcium as the oxalate salt and somehow manage to crystallize it, forming elongated needle-like crystals. They're known
as raphides or druses.
I think they only occur inside the cells, but it seems possible they could be used as a structural element in thistles.unionised - 12-7-2023 at 23:56
Exactly, cellulose with lignin.charley1957 - 13-7-2023 at 09:37
I remember a trip to the Botanical Gardens in San Antonio where I learned of a plant that grows along the edge of the water that was used by pioneers
as a pot scrubber. The plant was a thick-stemmed plant with minuscule leaves, mostly it was all stem and very tough. A quick search of the internet
failed to find out what it was, but I remember at the time how fascinating it was to find out that these plants were just loaded with silica
throughout their structure, which gave them the properties exploited by early Americans.charley1957 - 13-7-2023 at 09:51
https://doi.org/10.1093/aob/mcm247
A further search found this article which makes mention of the fact that silica as a major component of the stinging hairs of stinging nettle. Also I
found this https://en.wikipedia.org/wiki/Equisetaceae which revealed that the plant I remember was known as Equisetum, or colloquially as scouring rush, due
to the abundance of silica in its stem. clearly_not_atara - 10-8-2023 at 17:16
Those needles, phytoliths, are microscopic, measured in micrometers. Needles like those on thistles are macroscopic and not made of silica nor calcium
oxalate.
