I keep finding these tiny brown ridged "seeds" that appear on the leaves of my indoor plants. Since seeds don't normally fly, I am guessing they might actually be related to an insect. But the only insects I am aware of having in my living room are fungus gnats, lady bugs, and probably aphids, and these don't look like the eggs or pupae of any of those.
The nearby plants are: old basil, young batavia lettuce, young lambs lettuce, wood sorrel, a young avocado tree, and a baby philodendron erubescens. But I don't see how any of these could be producing these "seeds".
Thanks in advance!