Which plan/herb/tree produces the most oxygen?

Answer 1

On a global scale, the blue-green algae (cyanobacteria) in the oceans and lakes produces the most oxygen. The great spruce trees of the northern deciduous forests of Eurasia and North America come in second.

In terms of a single organism... there are aspen trees that have a single root system, yet produce hundreds of individual "trees", thereby making them a single organism. I always wondered how big those really are. And, of course, there are enormous individual trees such as the redwoods of the west coast of the United States, or the giant tropical trees of the rain forests.

Truth be told, it would be almost impossible to measure the actual oxygen output of all the largest plants in the world to determine which one produces the most oxygen.

Answer 2

The phytoplanktons as a group in the ocean produce the most oxygen. The oceans occupy 70% of the earth's surface.

Answer 3

I have no specific answer, but the one that absorbs the most CO2 would seem reasonable. If it takes up the most CO2 then it will be the fastest producing C compounds, and hence growing. So the fastest growing plant would seem the answer.