Sabine Wilms has the superior category as "Upper Medicinals". It is good to consider trees in the winter. They are actually available for harvest. Evergreens like Hemlock (Tsuga) and Pine can be harvested for needles or bark. Further, the trunks of the trees remain after the leaves and fruits have fallen. Regarding botany, it is time to study bark and buds. It also happens that many of the barks are very appropriate in the winter. The evergreens are good for their vitamin C and other fresh constituents, in addition to treating colds, flu, and fevers. Cinnamon is a good warming medicinal. Slippery Elm is good for supplementing the fluids. (Of course, The Divine Farmer's Classic of Materia Medica lists a Chinese Elm, Ulmus pumila.) Cherry Bark is another medicinal for coughs. And there are many more examples besides. Let's consider the medicinals listed by the Divine Farmer in the superior or upper class of medicinals.
See my new article: 5 Poisonous Plant Families the Survivalist Should Know & my Poisonous Plants Page
Nathaniel Whitmore, herbalist