Tiny trees, forced upon children, tolerated by adults, probably lol

A word for plain and simple, which always amused me as it is anything but plain. In the food world, it comes in a bean, though somehow beavers got involved.

I was once thought indivisible, Yet division made me countless. I rest within your hand, Lurk beneath your skin, My kin divide without ambition, Yet one alone hungered for perfection. Some carry a personal me everywhere. Some are merely crowds of me pretending to be one. Others pray never to wake inside me.

Barren and frozen, I'm a cold climate zone; some life exists, but mostly you are alone. Found in elevation, or close to the northern pole, this ice-cold wasteland can make you snowblind.

What has many needles, but doesn’t sew or thread?