Fabaceae (bean family) Acacia

Acacia Notes

The name is derived from the Greek akis in reference to the sharpness of the leaves (or perhaps thorns) of the plant known to the Greeks (A. arabica). There are over 700 species of Acacia in Australia, where A. pycnantha is the national floral emblem. There are many more in Africa; in ancient Egypt acacia was associated with life after death, and the custom of burying an acacia spray with the departed is continued today in some societies.

One species, A. greggii (now Senegalia greggii), is native to the continental United States, surviving on as little as 3 inches rainfall in the Mojave Desert; it has been drawn on as a source of gum. The valuable A. koa grows in Hawaii; the champion koa, in the District of Kau, stood at 140 feet in 1969. Giant trees 30 feet around can be seen. Traditional artifacts from acacia included dugout canoes and surf boards.

The wood is generally very hard and attractive for carving; koa wood, known as Hawaiian mahogany, is an example. Many species exude copious gum (such as gum arabic, obtained from several North African acacias) that has pharmaceutical and industrial uses as well as being added to food. The gum from A. decurrens, found on campus, is chewable, but tends to stick to the teeth. In 1827 Peter Miller Cunningham (1789–1874) wrote in Two Years in New South Wales, “Acacias are the common wattles of this country… Clear transparent beads of the purest Arabian gum are seen suspended in the dry spring weather, which our young currency bantlings eagerly search after and regale themselves with.”

Seeds of some species are eaten. Survival on “bush tucker” is taught by the Australian military and has caught the interest of the public, so that “wattle seed,” for example, is obtainable in health food stores.

There are two kinds of acacia, those with bipinnate leaves only and those that develop phyllodes instead of leaves. Phyllode is botanical Greek for “like a leaf.” If you can catch a seedling at the stage where it still has a few feathery leaves, and phyllodes are beginning to form on the same stalk, it is a sight to behold. Several acacias live for only 20 years or so and, with the coming and going of fashions in the landscape architect community, few if any have been planted on campus in the last quarter century. Consequently, many locations noted in the 1973 version of Trees of Stanford and Environs are no longer occupied, though regeneration has occurred here and there. Pruning after flowering preserves vigor.

Specimens noted in 2000 include A. decurrens and A. longifolia, whose attraction is their splendid floral display as early as February or even January, demonstrating a faith in the future not shared by many of our deciduous trees. A. melanoxylon, which is not short lived, is a reliable frost-resistant occupant of difficult locations. In Europe, feathery Australian acacias are commonly called mimosa, in particular by florists. In America, the silk tree (Albizia julibrissin) is often called mimosa. In neither usage is the glossy Mimosa intended. Acacia pollen being heavy is not carried far by the breeze, but gets the blame for irritation caused by pollen from less showy flowers (those of the live oak for example).

The Greek Ακακία is thought to have applied to the biblical shittah tree, of whose wood the ark of the covenant was fashioned. Many copies of the ark have been made to the precise published dimensions, but none was as dangerous as the original. When the Philistines captured the ark and placed it in the temple of Dagon in Ashdod (west of Jerusalem), the image of Dagon suffered damage and so many Philistines died of emerods (more likely dysentery) that the ark was expelled on a cow-drawn cart, driverless for safety; on arrival within the land of Israel at Beth Shemesh, it was unfortunately unloaded by unauthorized Jewish farmers, 70 of whom died. On the ark’s way back to Jerusalem, Uzzah, a good man whose name has been remembered for more than 3000 years, inadvertently touched the ark to balance it, and was struck dead. So also were Nadab and Abihu, sons of Aaron. When Moses and Aaron originally brought the ark to Israel, the tent that enclosed the ark at campsites during the wanderings in the desert had to be open at the top; the ark was so potent that it caused the air above the tent to glow red at night. Only the high priest had the knowledge for tending it safely.

About this Entry: The main text of this entry is from the book Trees of Stanford and Environs, by Ronald Bracewell, published 2005. Minor edits (Jan 2023, SP).