I first learned of Black Spruce (Picea mariana​) through my friend Maya, an aromatherapist who has given it to me numerous times as essential oil - simple and in blends.  I really enjoyed it that way and used it on troubled joints.  Various parts of the tree have been used by Native Americans for skin, internal ailments, diarrhea, burns, rashes, scabs, sores, toothache, venereal disease, wounds, respiratory infections, digestion, kidneys, stomach pains, and infections (Moerman Native American Ethnobotany).

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The Divine Farmer's Materia Medica lists Gardenia, Bamboo (foliage), Phellodendron, Wuzhuyu, Mulberry (root bark), Elm (preparation of fruit), Bitter Orange, Magnolia (Houpo - Magnolia officinalis & spp.), Ash, Prickly Ash, Dogwood, Chinese Trumpet Vine, Umbrella Polypore, Jujube (thorns), Longan, Lily Magnolia (Mulan - M. liliflora), Mulberry Mistletoe, Weeping Willow (catkin), Winged Wahoo, Mimosa, Usnea, Ganqi, Shinan, Creeping Prickly Ash, Goldenrain Tree (flower), Baisuichengzhongmu ("Tree In The Midst Of The Hundred Year City")...

See the post in materia medica on the Upper Class of Tree Medicinals: link  The article was a little further along, until chrome failed, once again, on my old computer.  I will get back to it later.  See also below for an earlier post on the subject.
It is interesting that The Divine Farmer's Materia Medica considers trees a certain group of medicines.  Groupings used today are often based on chemical constituents or main (known) medicinal properties.  In my mind, trees have a distinct energy that is worth considering in the context of healing.  In other words, I think they should be in their own group.  This thinking is largely what inspired my Forest Blends, which have been very successful formulas.

Collection of images.

Here we will discuss the three classes of woods in The Divine Farmer's Materia Medica.  I am using the Blue Poppy edition.
More here:  Herbs Superior Class; Herbs Middle Class; Fruits & Vegetables.
The Divine Farmer's Materia Medica classifies herbs by category (Jades & Stones, Herbs, Woods, Animals, Fruits & Vegetables, and Cereals) into three classes (Superior, Middle, and Inferior).  Here we will consider the trees.  The links above and future posts (except, perhaps if related to the subject of woods) will occur in the Materia Medica blog.