Calcium oxalate (CaOx) crystals have challenged human curiosity since the advent of microscopy. These crystals are linked to the control of calcium levels in plant cells, but they have also been attributed several other functions, including protection against herbivory. However, the protection offered by CaOx crystals against herbivory may be overstated, as claims have been mainly based on their shapes and hard and indigestible nature rather than on experimental evidence. I contend that it is improbable that a constitutive defense, present since very early in the evolution of plants, has not been superseded by herbivores, especially insects. Here, I present arguments and evidence that suggest that these crystals have low efficiency in protecting plants against herbivores. First, I argue that insects with chewing mouthparts possess a semipermeable structure that protects their midgut, minimizing damage from crystals. Second, the action of CaOx crystals is purely mechanical and similar to other inert materials such as sand. Therefore, CaOx crystals only provide effective protection from herbivory in very particular cases and should not be considered an effective defense without supporting experimental evidence.

自显微技术问世以来，草酸钙（CaOx）晶体一直挑战着人类的好奇心。这些晶体与植物细胞中钙水平的控制有关，但它们还被归功于其他几种功能，包括对草食动物的保护。但是，CaOx晶体对草食动物的保护作用可能被夸大了，因为声称主要是基于它们的形状，坚硬和不易消化的性质，而不是基于实验证据。我认为，自植物进化的早期就存在的本构防御没有被草食动物，尤其是昆虫所取代，这是不可能的。在这里，我提出了论点和证据，表明这些晶体在保护植物免受草食动物的侵害方面效率很低。第一的，我认为具有咀嚼口器的昆虫具有半透性结构，可以保护其中肠，从而最大程度地减少晶体的损害。其次，CaOx晶体的作用纯粹是机械的，类似于其他惰性材料，例如沙子。因此，CaOx晶体仅在非常特殊的情况下提供有效的食草保护，并且在没有支持实验证据的情况下不应被认为是有效的防御。