Stones in my salad

Bananas. Corn. Spinach. Peanuts. Beans. Squash. Rice. Apart from being plant foods, what do they have in common?

Add horsetails to the list. Does that help?

Horsetail

Following up on Gary Hurd's comment, I've been reading about phytoliths. (Pronounced "feet-o-liths") The word comes from the Greek "phyte", meaning plant, and "lithos-", stone.  These are microscopic structures in the tissue of plants, made of the mineral silica.

One of the major components of soil or sand is quartz, crystals of silicon dioxide, AKA silica. This silica is absorbed by plants, and deposited in or around their cells. When the plant dies, the organic part of the plant is digested by other organisms, including us, but the silica structure retains its shape. In our food, it is in the fiber, the husks of cereals, the pectin in citrus fruit, and in the water we drink (the same way the plant gets it in the first place; hard water has a high silica content.)

Some plants have a higher silica content than others, the ones I listed above among them. Horsetail has so much that it becomes inedible, but the stiffness makes it good for scrubbing pots while you're out camping. Those sharp hairs on the grass are supported and stiffened by silica.

I looked up a variety of plant foods that some people find irritating in large servings; spinach, pineapple, peanuts, cabbage, cucumber. It turns out that they are all high in silica.

In reasonable amounts, though, silica is probably a necessary part of our diet. It improves the strength and elasticity of skin, hair, and nails, may reduce heart disease and slow aging.

There's more: phytoliths have taught us history. I'll look at this tomorrow.