February - a black root that's white, too.
This weird and uncommon root, called viper's grass, black salsify or scorzonera in English, is making a comeback in Sweden, at least, and is available in a locally-grown, organic version at the largest grocery store called ICA. It used to be called "farmer's asparagus" because once the black sticky skin is peeled off it looks like white asparagus. It also must be soaked in water directly after peeling or it will unattractively discolor. If you aren't vegan, the root is great in a creamy gratin.
Photo of black root via Lord Nelson seed catalog.