Elaeagnaceae

Tough, hardy shrubs and small trees, immediately recognisable by the dense covering of silvery or brown peltate scales on leaves, shoots and fruit, which gives the whole plant a metallic sheen and, under a hand lens, a surface like overlapping parasols.

Their defining biology is nitrogen fixation — but not the legume kind. Elaeagnaceae form actinorhizal root nodules with Frankia, a filamentous soil actinobacterium, rather than with the Rhizobium of Fabaceae. It is an independent evolutionary solution to the same problem, and it lets these shrubs colonise gravel bars, dunes, mine spoil and burned ground. That same vigour makes several of them serious invasives in North America.

The family’s medical heavyweight is sea buckthorn, which is not here but sets the context for everything else in the family. Its fruit and seed oils are used for mucosal and skin healing, and are among the few plant sources of palmitoleic acid (omega-7), a fatty acid otherwise rare in the plant kingdom.

Soapberry is the family’s North American member and one of the least-studied plants in the boreal ethnobotanical literature. Its cultural importance is disproportionate to its research: the berries are whipped with water into the foamy preparation known as Indian ice cream or sxusem, a dish of real ceremonial and social significance across the interior Northwest. The foam is a direct consequence of its chemistry — the berries are rich in saponins, which is also why they taste bitter.

What research exists is compositional rather than clinical. Soapberry is notably rich in lycopene, and carries the unusual β-carbolines tetrahydroharmol and shepherdine alongside serotonin — an interesting profile with no pharmacological work behind it.

Carotenoids are the family’s most consistent feature, and the fruits are unusually dense in them: lycopene and methyl apo-6′-lycopenoate in Shepherdia, a wide carotenoid spectrum in Hippophae. Triterpenoid saponins account for the bitterness and the foaming behaviour of Shepherdia fruit.

Beyond that the family carries vitamin C in quantity, flavonoids of the usual kinds, and — in sea buckthorn — the rare palmitoleic acid. The β-carboline alkaloids reported in soapberry are an oddity in this family and remain uninvestigated.