Fagaceae

Beech family. The dominant broadleaf trees of the northern temperate forest — around 900 species in a handful of genera, of which Quercus alone accounts for roughly 500. Oaks, beeches and chestnuts between them define whole biomes, and where they grow they tend to grow in charge.

The family character is the fruit: a nut seated in a cupule, a woody cup formed of fused bracts. It is the same structure whether it appears as the acorn’s cap, the beech mast’s bristly four-part husk, or the fiercely spined bur of a sweet chestnut. Flowers are wind-pollinated catkins — small, green and unmemorable, in a family whose members are anything but.

Fagaceae medicine is tannin medicine, and oak is its reference point.

Oak bark (Quercus robur) is among the strongest astringents in the European materia medica and one of the few with formal recognition: the EMA’s herbal committee accepts it for mild diarrhoea, for minor inflammation of skin and mucous membrane, and for haemorrhoids. American practice used white oak (Q. alba) the same way.

The action is physical rather than pharmacological, which is why it is so reliable and so easily misunderstood. Tannins bind and precipitate proteins, so on inflamed or weeping tissue they draw the surface together, reduce secretion, and lay down a thin protective coagulum over damaged mucosa. That is the whole of astringency, and every traditional oak-bark use — the gargle, the sitz bath, the anti-diarrhoeal decoction, the wash for a weeping skin lesion — is the same effect applied to a different surface.

The same chemistry sets the limits. Tannins do not distinguish between the proteins you want them to bind and the ones you don’t, so they reduce absorption of iron, alkaloids and some drugs taken at the same time, and irritate the stomach in quantity. The EMA caps oral oak bark at three to four days and topical use at two to three weeks for precisely that reason. Astringents are short-course remedies by nature.

Two footnotes worth keeping straight. Robuvit, the standardised extract behind most modern “Quercus robur” trials, is made from oak heartwood, not bark — a different preparation whose fatigue and oxidative-stress findings do not transfer to a bark decoction. And acorns are food across much of the northern hemisphere, but only after repeated leaching; the tannin load that makes the bark medicinal is what makes the nut inedible raw.

Both tannin classes, in quantity. The hydrolysable ellagitannins — castalagin and vescalagin chief among them, alongside gallotannins and free ellagic and gallic acid — dominate oak bark and heartwood, and are what oak-aged barrels give to wine and spirits. Condensed tannins (proanthocyanidins) sit alongside them, with flavonoids including quercitrin.

The flavonoid quercetin takes its name from this family — from quercetum, an oak wood — which is a fair measure of how central these trees were to early plant chemistry.