How Can You Tell a Lysiloma from an Acacia?

Feathery leaves, pale puffball flowers – is it a Lysiloma or is it an Acacia? Inquiring minds want to know!

What is in a Name?

Bear with me here as we start with some history and botanical exploration. If you get bored you can skip to the final paragraph – but I hope you won’t.

Thorny acacia in the Negav desert. Camels eat these, despite the thorns.

Acacia are a group of trees in the Legume or Pea Family. “Acacia” was first described by the Swedish botanist Carl Linnaeus in 1773 based on the African species he called Acacia nilotica. The name Acacia comes from the Greek word for thorn = “akis.” The species name “nilotica” was from this tree’s best-known range along the Nile river.

As botanical explorers wandered the globe and they found many plants with highly similar flowers, fruit, and thorns. Similar plants found in similar habitats – so were tucked in with the thorny Acacia. Then the botanists got to Australia (remember Botany Bay?). Anyway, there were even more similar plants – only they lacked thorns. Still, they seemed similar enough so they got stuck in the Acacia genus as well.

Sometimes you have to look closely to see the thorns – but they are there! Photo courtesy of Z. Akulova.

One of These is Not Like The Other One

Meanwhile, here in the Americas, botanical explorers found a new plant (now Lysiloma). Note that botanical explorers are not generally the same as the botanists naming plants. Explorers collect specimens, dry them, and ship them back to Europe for naming. This is where the brilliant botanist Bentham got involved.

George Bentham spoke 6 languages before he was ten years old.

Puffball flowers – check. Feathery foliage – check. But wait – there’s no thorns! Bentham wanted his world to have better order so he came up with a new genus with a new name that fit this pretty plant with delicate feathery foliage. He came up Lysiloma. Lysiloma comes from the Greek lysis for loosening and loma for edge or fringe. Loose, frilly fringed leaves.  No thorns!

So the Answer Is – ?

Acacia have thorns. Lysiloma don’t. ? Sorry – Not quite!

Those Australian Acacias

Here is where the answer gets convoluted. As of 2005, American acacias aren’t acacias anymore. Scientists in laboratories staring at DNA sequences decided that – even though acacia flowers all look the same, and the plants all grow alike, and even and have similar mycorhizal relationships, and you can’t see any differences with your naked eye or even a hand lens – they are not in the same genus.

One of the Argentinian “acacia” – with thorns – although not technically an acacia any more. Photo courtesy of Z. Akulova.

In 2005, the Acacia genus was divided into five separate genera by the International Congress of Botanical Nomenclature. 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. In 2005 the meeting was in Australia, and they were able to pack the vote.  All the Australian Acacia stayed Acacia and all the rest got changed. (The International Congress for Botanical Nomenclature only meets every so often.)

So the Real Question Should Be –

Is it Lysiloma or Acacia, Vachellia, Senegalia, Acaciella, or Mariosousa?

Vachellia, Senegalia, Acaciella, and Mariosousa all have thorns. Acacia in the strict botanical sense come from Australia and they don’t. Lysiloma come from the Americas and they have no thorns either.

Acacia podalyriifolia, the Australian pearl wattle. Photo courtesy of R Vanderhoff.

So how can you tell? Australian Acacia have a chemical complex that all other “acacia” do not. This gives them a blueish green cast that you will not see in those others. You will also see that color in Senna and Cassia which tells us that the Australian plants have the common ancestor of Cassia – but that’s a whole ‘nother can of worms. Along with that bluish cast the Australian Acacia have leaves that are generally thicker and more leathery than the other genera.

Acacia saligna, one of the Australian willow acacias. Note the stiff leathery leaves. Photo courtesy of R Vanderhoff.

Final Answer – The Million Dollar Answer!

Green leaves, puffball flowers, no thorns = Lysiloma
Green leaves, puffball flowers, thorns = Vachellia, Senegalia, Acaciella, or Mariosousa
Blue-green leaves, leathery leaves, puffball flowers, no thorns = Acacia

Lysiloma divaricatum in Chihuahua Mexico. Photo courtesy of T Lebgue.

Another post will have to cover Vachellia, Senegalia, Acaciella, and Mariosousa.

Hope you enjoyed this glimpse into the world of Botanical Nomenclature



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Featured photo: Lysiloma microphylla variety thornberi.  Courtesy of J. Pawek

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