A species
Nori seaweed
Pyropia yezoensis
The red seaweed wrapped around sushi.
You and the nori seaweed last shared an ancestor about 1.8 billion years ago (on 28 July, if life's history were one year).
The dark wrapper around sushi is often nori, a red seaweed farmed on nets in shallow bays. It may look like thin paper, but it is a distant cousin of all land plants. That family tie is surprising, because nori has no true roots, stems or leaves.
In the wild, it grows as a paper-thin sheet up to about as long as your hand, fixed to rock by a tiny disc. Fresh blades look soft purple-brown to red-brown or olive, not bright red. Dried shop sheets are cut into flat squares about as wide as a tea saucer, and turn black-green to dark purple.
Nori lives on rocky shores where waves cover it at high tide and sun and wind leave it bare at low tide. Its reddish colour comes from a special pigment that reflects red light and soaks up blue light. In red seaweeds that live deeper, that helps them make food from sunlight where the water is bluer.
Dries out and comes back to life
At low tide a blade can lose about 95 percent of its water. Like a dried sponge, it soaks up water and carries on when the tide returns.
A secret life inside shells
Nori has a second form made of pale threads too small to see that tunnel into shells. People thought the threads were a different living thing until a scientist linked them to nori in about 1950. That find helped farms grow much more nori.
Useful food for vegetarians
Dried nori holds useful vitamin B12, plus iron. Most other edible seaweeds have little or none of this vitamin.