For the greens:
1. Rinse and trim the greens. If using collard greens, remove the tough inner rib.
2. Fill the sink with cold water and submerge for about 5 minutes to remove sand and grit. Move greens to colander then drain sink to leave dirt at bottom of sink.
3. Chop or tear the greens into large pieces and place in a large saucepan with a tightfitting lid. Add water and season generously with salt; place over medium-high heat. When the water in the pot begins to simmer, tightly cover and reduce the heat to medium low. Cook the greens, stirring occasionally, until soft and wilted, 15 to 20 minutes.
4. Strain the greens, being sure to reserve the cooking liquid, about 3 1/2 cups. Cool greens slightly then chop into 1/2-inch pieces. Take about half of the chopped greens and puree them in a food processor and set aside. Add a little of the reserved cooking liquid if the greens will not blend.
For the gumbo base:
1. In a large, heavy-bottomed pot heat the oil over medium heat. Create a roux. Slowly sprinkle in the flour, stirring constantly with a whisk to preven any lumps from forming. Reduce the heat and cook stirring constantly until it is a nutty brown color (like peanut butter) and emits a toasted aroma, 10 to 15 minutes.
2. Use a wooden spoon to stir the onions, scallions, bell pepper, celery and garlic into the pot. Season with salt and ground black pepper. Cook, stirring often, until vegetables are softened, about 5 minutes.
3. Add the reserved cooking liquid along with the vegetable broth or water, stirring until well incorporated. Increase the heat to medium high and bring the mixture to a simmer. Stir in the measure salt, Cajun seasoning, cloves, allspice and bay leaves and simmer, stirring often, until the gumbo base is soupy and thick and the vegetables are tender, about 15 minutes.
4. Stir in the chopped and puréed greens and marjoram; cover the pot and simmer 10 minutes. Add Tabasco to taste and serve over cooked white rice, garnished with thinly sliced scallion tops.