There is a field of grass that is so green and fresh and untouched by the grazing of animals. Throughout the entire day it glistens in the sun as if it is still covered in the morning dew. But beware, young shepherd, for that pasture is mighty treacherous and will cut you if you so much as dare step on it barefoot. And if your animals accidentally graze there? Be prepared to slaughter them as they are not long for this world anymore. Throw away their innards as you do, they're not safe to eat anymore.

Tl;dr the grass has evolved to grow into being like glass.

The idea for this comes from the silica phytoliths of many grass species, in particular sword grass that can cut human skin and discourages animals from grazing. I want for the phytolith production of a grass species to be so exagurated that they may look like your usual green grass from afar but up close it will be hard to not simply refer to them as green glass. They're still plants, but their phytoliths are produced and deposited in such ways to make them look and act like glass shards.

My question has to do with if growing such a structure is at all viable for a grass like organism, or if having such a rigid silica structure as part of its body will inhibit its growth(and possibly stop it dead in its tracks if the growing parts end up encased?)

Would grass still be able to thrive if it grew into being like green shards of glass?

  • $\begingroup$ Adding to @JohnO 's wonderful answer pretending to be a comment, if the grass also developed enzymes to consume spilt blood from the soil, that would make your glass blade adaptation into an aggressive food acquisition trait in addition to its initial defensive function. $\endgroup$ Commented Dec 23, 2021 at 16:10
  • $\begingroup$ Have you never cut yourself on grass? It's like a papercut, it hurts more than it should for the size of the injury. $\endgroup$
    – Separatrix
    Commented Dec 24, 2021 at 9:18

4 Answers 4


Why Not?

There is nothing intrinsically wrong with a plant creating a rigid and sharp structure, especially as a defensive one. There would need to be an underlying ability to adapt to breakage - either treating it as budding, or having underlying flexible structures so breaks can bend. Wood is rigid, but also flexible. there would need to be a trade-off.

It might be useful, but it would be far from a knock-out advantage over other plants. Otherwise, I'm confident something would have evolved to do this (and maybe it did - how would you tell if this was the case for a fossil?)

Growing parts will likely be soft. Grass grows from the base, an adaptation that lets it be eaten off and still grow. So the grass will be able to suffer damage and still grow. And there will be damage. With fragile glass, even a stiff wind could cause breaks in the structure.

And despite its glassy structure, something will evolve to eat it eventually. There are people who eat glass, and if it's relatively fine, the digestive system often is able to pass it. How much easier for something like a goat, well known to eat nasty foreign objects. An animal with tough skin or shell could likely take refuge amongst such grass as a defensive measure from predators. An animal could also chew the glass with just teeth in a tough mouth, digest the nutrients out, and swallow the digestive liquid and spit out the crushed glass. But since the plant has spent its resources making indigestible glass rather than potentially digestible cellulose, the payoff for the (silicavore?) is less than for other plants.

A potential strategy for these plants would be to grow glassy barbed seeds so animals would get stuck by the seeds. Then these seeds could get torn out elsewhere, or potentially fester and kill the animal stuck by it. Instant fertilizer!



Most designs in nature are already quite smart. Evolution has fine tuned a plant's physiology to serve its purpose, in a certain environment. In this case, to assert your idea, you could try to reason why certain properties exist, specifically, why grass benefits from a certain flexibility,

1] Seeds I really wonder if a glass container would work out for the grass seeds in a positive way. The grass as we know it uses the wind and animal's digestive tracts, to spread its seed. The seeds are mounted with a soft connection, in soft tissue, easily released. Now suppose you'd protect the grass from animals by sharpening the leaves, make them more rigid, that would protect from grazers, but same time, inhibit the animal digestive tract route, for spreading the seeds ! and it could also be more difficult for the grass to release seeds on its own. It would always require wind, maybe stormy wind, to spread its seeds.

2] Sunlight An impairing aspect of having very rigid grass leaves: it imposes a fixed position i.r.t. the sunlight. A grass leave will bend and torque, to optimize its angle/posture for catching sunlight. These properties would vanish, when the grass gets rigid overall, like cactuses are. Cactuses generally live in environments with abundant sunlight. For grassland, that is not always the case.

3] Recovery A powerful treat of current grass plants: their flexibility allows the grass to survive heavy pressure. Your glass plants will not provide protection from certain animals treading the grass. Hooved animals, or large animals with elephantine feet will not be disturbed by your glass leaves.. but the glass leaves can't recuperate, they will be broken forever.

Reeds have flexible leaves.

There exist plenty of grass species, that produce reeds. These are very rigid. Humans can make sharp arrows and pens out of these reeds. But if you look at the reeds closely, you see it has flexible leaves on the side, all around. These leaves are needed, apparently, having only a rigid shaft won't do for energy.





I am digging it. How about macroradiolarians?

Your glass grasses are scaled up radiolarians. These organisms construct glass shells or tests and house within them photosynthetic endosymbionts. Your glass grasses are no longer free living but sessile in the manner of corals. Perhaps in some John Daileyesque alternate timeline these creatures are reefbuilders. Their fractal-like structures are well suited for scaling up because they are fractals - they just keep adding to them. The glass houses they build out of soluble silica shelter copious green endosymbionts. At low tide, the glassy spikes and spires protrude from the reef into the sunny air, catching the light.


In the context of the Question, yes, of course it would… by definition. That's broadly a simple re-statement of the theory of evolution.

If grass - or anything else - grew into (whatever) it would necessarily be able to thrive in that state.

In that context, how are shards of glass different from grains of sand or sticks of chalk?


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