Rosemary
Some use this herb for cooking, other use it as an herbal tea.
As with all plants having needle-like leaves, the rosemary is evergreen. It can be held indoors for the entire winter season and still give off a pleasant aroma.
Most needle-leafed plants are very good purifiers, especially for humid winter air. They breathe carbon dioxide and exhale oxygen. Rosemary is no exception here.
The most important function of this herb is its ability to improve cognitive function and shield the brain from free radicals.
Also, the presence of this plant in the room is enough in the long run. Rosemary still exhales some of its essential oils in the room (you don't need to boil it in a tea infusion to benefit from it).