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Imagine a field of plants that when walked through cuts human skin. Unlike a Stinging Nettle, the leaves would have to have razor-like edges, without the trichome hairs. The leaf edges should cause a finger to bleed if it were lightly dragged across the skin. The plant can be any height, shape, color, etc., but preferably about the size of a sword fern. The razor characteristic also needs to be consistent across seasons (it's not a rare event).

How would these plants achieve their sharpness? Would metals absorb through the soil accumulate in the leaves? Could a symbiotic relationship help achieve organic razors?

Bonus points if the plant is sharp enough to potentially kill or seriously injure someone while walking through a field.

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    $\begingroup$ That's called a cactus. $\endgroup$
    – The Square-Cube Law
    Commented Jan 10, 2021 at 20:25
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    $\begingroup$ @TheSquare-CubeLaw To clarify, I am looking for a plant that does not use spines or trichomes to damage organisms. It must use a long continuous razor-like edge on the leaf. $\endgroup$
    – Mandelbrot
    Commented Jan 10, 2021 at 20:28
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    $\begingroup$ Q:"What would make a plant's leaves razor-sharp?". A:"Earth as it is now". I'm assuming OP has never had to walk naked through a sawgrass field. $\endgroup$
    – PcMan
    Commented Jan 11, 2021 at 6:28
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    $\begingroup$ Have you ever walket through a corn field? $\endgroup$
    – Hobbamok
    Commented Jan 11, 2021 at 13:14
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    $\begingroup$ Ever heard on what to wear when harvesting sugarcane? Clothes from head to toe, because in addition to the potential snakes and certain bugs, the leaves are pretty sharp and can easily cut human skin unless you're careful. $\endgroup$
    – ProjectApex
    Commented Jan 11, 2021 at 13:49

2 Answers 2

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Glass

Some plants already sequester minerals in order to form blades in their surface: grasses and phytoliths. Phytoliths are thought to be at least in part a defense mechanism against herbivory, abrading the mouthparts of insects and ungulates and releasing chemicals with their breakdown that further degrade vertebrate enamel.

It's just a small step from that to go from micro-blades that merely wear down teeth to macro-blades along the edges of leaf margins that shred any animal that comes too close. We already have modern examples for a comparable phenomenon: obsidian blades, which can be razor-sharp and slice into organic tissue very easily. To stop obsidian blades you almost need to be protected by metal or stone. And because these structures are being grown, not carved or manufactured, the plants can manipulate the formation of the blades on an almost nano-structural level to maintain maximum sharpness.

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    $\begingroup$ en.wikipedia.org/wiki/Sword_grass. The one I am more familiar with is pampas grass which people in the US like as a durable ornamental. That stuff will slice you to ribbons, no joke. thriftyfun.com/… $\endgroup$
    – Willk
    Commented Jan 10, 2021 at 20:12
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    $\begingroup$ @Willk Completely forgot about swordgrass or sawgrass. When I was in Florida I was told never stick you arm out in a moving airboat: your arm will get severely lacerated $\endgroup$
    – user2352714
    Commented Jan 10, 2021 at 20:14
  • $\begingroup$ Since diatoms can already deposit similar structures, it would just be a matter of having a plant evolve the appropriate growth characteristics. Would you need a particular mineral/nutrient source to make this viable? Most such structures would likely be very fragile and even a stiff wind causing them to bang together would dull the effect. Maybe more of a saw-tooth edge? I'm trying to think what the energetic costs of this would be... $\endgroup$
    – DWKraus
    Commented Jan 10, 2021 at 21:22
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    $\begingroup$ @DWKraus Grasses get theirs from the soil (silica). Soil is 60-70% silicon dioxide, and that ratio can be as high as 90% in some Australian soils. Sounds pretty doable. $\endgroup$
    – user2352714
    Commented Jan 10, 2021 at 22:49
  • $\begingroup$ @user2352714 thx, wasn't sure if it needed a particular mineral content. Haven't studied botany as much as other things. Thinking the edge would look a bit like a macuahuitl at the micro-level then (referencing the obsidian blades) $\endgroup$
    – DWKraus
    Commented Jan 10, 2021 at 23:01
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Try the Yucca

When it comes to plants that have sharp edges, many gardeners may immediately think of plants like succulents and cacti... however, many other sharp leaved plants are available in the form of palms and ornamental grasses... In many cases, plants that have sharp edges can easily injure gardeners or their guests when planted in less than ideal locations. Sharp plants, such as the yucca, have the potential to seriously injure those who come into contact with its leaves.

Read more at Gardening Know How: Plants With Blades: Using Plants That Have Sharp Edges In The Garden https://www.gardeningknowhow.com/ornamental/foliage/fogen/gardening-with-sharp-leaved-plants.htm https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/growing-pampas-grass.htm

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    $\begingroup$ As someone who grew up digging and planting tree form yucca I can confirm they will cut your hands and arms to ribbons. $\endgroup$
    – John
    Commented Jan 10, 2021 at 23:17

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