Out West, the green plant is considered a pest, and you find it everywhere. It is very dark green and has one vertical stem which has the seed pod on top. The leaves grow flat on the ground. My igs and I used to eat it.
The other plantain is a close cousin to the bananas we get. Sometimes my food store has several types of banana-like fruits, and I don't know if they are all called plantain. The one I buy is larger than a regular banana, has thicker skin, and has a starchy fruit. i don't like the taste of raw plantain, so I peel and slice it and lightly fry (I will try steaming it next time) it in light oil. That makes it slightly sweet along with it's other natural flavors. IMO this fruit is more nutritious when cooked.