Acacia – Part I

As I write this the native white thorn acacia (Vachellia constricta, formerly Acacia constricta) are blooming in my yard.  I love the fragrance.  So close to sweet peas!  Gentlemen may seek out sweet smelling roses with which to woo the fairer gender, but as a Southwester gardener, I far prefer the sweet smelling acacias around my garden.  Oh, wait, I forgot, they aren’t technically “acacia” anymore.

White thorn acacia. Image courtesy R. Spellenberg.

Quick Look at Acacia Names

Acacia is a genus in the Legume or Pea Family.   Their puffball flowers put them in the Mimosa subfamily.   The genus was first described by the Swedish botanist Carl Linnaeus in 1773 based on the African species Acacia nilotica.    The name “acacia” derives from the Greek word for thorn “akis.”    The species name “nilotica” was given by Linnaeus from this tree’s best-known range along the Nile river.

Many plants with highly similar puffball flowers, thorns, and legume pea pod fruits were found in other desert habitats as botanists explored the globe. They were added to the Acacia genus because they were thought to be closely related (and they are).  Down in Australia there were a number puffy flowered legumes but they lacked thorns. Other than that, they seemed highly similar so they added to Acacia as well.

By the way, Acacia is the scientific name, and acacia is the common name.  We see this happen with Iris and iris as well.

Puffball flowers puts these all into the Mimosa tribe of the Legume family.

Gene Jockeys Rearrange Names

Now days, so-called “botanists” do not get all hot and sweaty looking for real living plants in the wild. Now they stay in air-conditioned laboratories and sequence DNA from the plants collected years ago by field botanists. And now these gene jockeys decided that – even though acacia flowers all look the same, and the plants all grow alike, and even and have similar myccorhizal relationships, and you can’t see any differences with your naked eye or even a hand lens – these “acacia” were not in the same genus.

One of the Australian “wattles.”

In 2005, the genus Acacia was divided into five separate genera.    Now we have Acacia, Vachellia, Senegalia, Acaciella and Mariosousa.    But don’t change your plant labels yet, or even bother to learn the new names, debate rages on and may take a while to settle.  There is still no such thing as portable DNA sequencers with which to identify plants.

A for Acacia

My Botany Alphabet book would start with “A” for Acacia.    (And Z is for Zephyranthes,)

My desert Vegetable Garden Alphabet book would start with Arugula, but that’s another story.

Acacia Down Under

In Australia, Acacia are generally referred to as wattle or mulga.    The Australian national flower is golden wattle (Acacia pycnatha), a native of the cooler southeast coast, and not at all suited for our desert Southwest.   That said, a number of the Australian acacias will do okay here, in temperatures up to 115 and down to 15 degrees.

Coarse and leathery “leaves” on the wattles.

Most of these Australian acacias tend to have large, thick leathery “leaves,” rather than the smaller finer, fern-like leaves of the African and American species.    Thus they have a coarse design texture. This means that you think twice about plopping them in next to a fine textured tree like a mesquite (Just say “No!”).

Science Nerd Notes

soule-garden-successTechnically these “leaves” are “phyllodes” not true leaves.

The writer responds. “Most of my readers are NOT scientists, and since they look like leaves, and they act like leaves, so I called them leaves.

List of Australian Acacia

So far a fair number of the Australian acacias have been introduced to our shores and are available in nurseries.  Here they are alphabetically by scientific name.

Mulga tree (Acacia aneura), greyish weeping tree, 20 feet by 10 feet wide.

Coarse textture when not in flower. May be hard to look right in the landscape.

Leatherleaf acacia or broadleaf mulga (Acacia craspedocarpa), blue grey shrubby tree to 10 feet tall and wide.

Coonavitta wattle (Acacia jennerae), blue grey weeping tree to 60 feet tall, 30 wide.

Sydney golden wattle (Acacia longifolia), blue green shrubby tree to 20 feet tall and wide with golden flowers.

Mallee golden wattle (Acacia notabilis), silvery shrub reaching 6 by 6 feet with golden flowers. Very drought resistant and tolerant of alkaline soils.

Weeping myall (Acacia pendula), grey-green weeping tree to 40 feet, spreading to 20 wide. Avoid planting in a pool-scape, it seems to shed leaves daily.

Waddywood (Acacia peuce), fine textured silvery tree to 20 feet tall and as wide.  Prefers sandy soils.gardening-with-soule-acacia-landscape-flowers

Ongerup wattle or prostrate acacia (Acacia redolans), grey green groundcover reaching 2 foot tall and 10 feet wide, popular on golf courses.  If your golf ball goes into one of these, take the penalty and play a new ball.  Mice, rats, rabbits – and the snakes that eat them (!) – all love it under these plants.  As shown in my YouTube – never put your hands where you don’t have a clear line of sight.

Willow acacia (Acacia salicina), grey green weeping tree to 30 feet tall, 15 wide.

Blue leaf wattle or weeping wattle (Acacia saligna), fast growing single-trunked tree to 20 feet tall and almost as wide, with striking blue green leaves and golden flowers.

Last and by far most popular, shoestring acacia (Acacia stenophylla),  a grey green tree rapidly reaching 30 feet with a partially see-through canopy. Avoid over watering.

Use in Landscapes

With their silvery blue or grey green tones, Australian acacias can possibly work well in local landscapes, especially with a backdrop of a tan or white home.   gardening-with-soule-acacia-landscape-flowers

One note of caution.    Many of these Australian acacias come to us from areas that commonly have brush fires.  This means that their genes are urging them to sprout freely from the roots.  These sprouts will grow fast to become new trees.   Whole entire groves of new trees.    In the right yard, this can be a bonus.    In a small yard, perhaps not a bonus. You have been warned.

What’s in A Name?

As Juliet said in Shakespeare’s “Romeo and Juliet”
“What’s in a name? that which we call a rose
By any other name would smell as sweet.”

And even if it is no longer an “acacia,” it still smells as sweet as ever.

Native white thorn flower. Image courtesy J. Doyden

In a future post we will revisit this topic and cover the American species and their new names.

Other Useful Desert Plants

This book features 25 native plants and 25 European introductions.

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A steal at only $22!  This link is to our sales site. The profits from the sale go to the Arizona-based Horticulture Therapy non-profit Tierra del Sol Institute.

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