Alnus cremastogyne Seeds | Sichuan Alder

Upright female catkins and broad shallowly lobed leaves on a Sichuan alder — Sichuan Alder (*Alnus cremastogyne*): Betulaceae, valley floors and river margins of the Sichuan basin.

LATIN NAME: Alnus cremastogyne

COMMON NAME: Sichuan Alder

Plant Profile

Sichuan alder is a tree of the flat valley floors and river margins of the Sichuan basin, and it grows the way a plant grows when its ground is periodically underwater. The trunk goes up straight and fast, often with a slight lean, and the crown stays narrow and open rather than spreading. Leaves are broad, roundish and shallowly lobed, with a wedge-shaped base, and they stay green late into autumn. Catkins appear in late winter before the leaves, the male ones long and pendulous, the female ones short and upright, and the small winged nutlets ripen by autumn and blow across the water. It reaches fifteen to twenty-five metres, rarely more, and lives fast rather than long. Along the Min and the Tuo it forms narrow galleries that hold the bank together through the flood season, which is the ecological job it does best.

Science & Biotechnology

Alnus cremastogyne is actinorhizal: it fixes nitrogen not with rhizobia but with the actinobacterium Frankia, which enters through root hairs and forms nodules with a woody core, a symbiosis shared with Elaeagnus, Casuarina and Myrica rather than with the legumes. That is why the tree can grow on raw silt and gravel with almost no nitrogen in it, and why its litter is rich enough to change the soil beneath it. The species is endemic to the Sichuan basin and adjacent parts of Chongqing and Guizhou, a narrow range for a tree planted so widely in Chinese forestry. Its pollen is shed in late winter and is a recognised allergen in the region. The wood is soft, pale and light, poorly resistant to decay in contact with soil, which limits it to uses where it stays dry.

Uses & Benefits

Its greatest use is land repair. Sichuan alder is planted along rivers and on unstable slopes to hold soil, and it is one of the first trees used on the raw cut slopes left by road building in the basin. The nitrogen it fixes improves the ground for whatever is planted after it. The timber is light and works easily, and goes into plywood cores, matches, packing cases and paper pulp, none of it durable. Locally the bark has been used for tanning and as a rough astringent, and the catkins for a yellow-brown dye. It is a fair fuel wood when seasoned. In gardens it is grown as a fast shade tree for wet ground and as a nurse for slower species, though its short life and brittle wood make it a stage in the planting rather than its destination.

Growing from Seed

Sow fresh seed on the surface of a moist, open mix and press it in; alder seed needs light and does not need cold, though a month at 4 degrees evens germination out. Keep the pot standing in a shallow tray of water, because the seedlings die if the mix dries even briefly, and give full light from the start. Germination takes two to four weeks. Prick out when the first true leaves are open, and pot into a mix with plenty of organic matter. The seedlings grow fast, thirty or forty centimetres in the first season, and can be planted out at that size in autumn. Choose a site that stays damp, and do not expect the tree to tolerate a dry bank, whatever its reputation for toughness.

Our Take

A fast, short-lived tree for wet ground and river banks, useful as a nurse and a soil builder. Plant it where the roots can reach water and do not expect furniture timber.

Tree Seeds