Our Macadamia Relative

One day toward the end of January, I looked over the western orchard wall to see a tree in bloom with interesting bottle-brush flower stalks or inflorescences.

 

I clipped a sample and took it home to more easily make notes and to try to identify the tree.

 

One feature I noticed more and more as I handled the plant was its odor – strong and peculiar. I couldn’t think how to describe it, but wrote in my notes that maybe you could call it “rancid green bean.”Another feature that stood out were the long leaf stalks, or petioles. Each leaf was attached to the stem by a stalk that was quite long – almost as long as the blade itself (see arrows in image below).

 

The leaves were stiff, but I didn’t know whether to call them “leathery.” I could tell the leaves were simple, as opposed to compound, that their edges were smooth, and that they were arranged in an alternate pattern. Yet I was not confident of my Family identification, and until I could be confident of the Family I felt I could go no further. I decided to put the identification of this tree on the back burner.

Then one day when doing a Google search for images of something else, a bottle-brush inflorescence showed up at a USDA site.

 

The inflorescences were not as stiff as mine, but I thought they looked pretty similar. The information that made my jaw drop, though, was that the USDA’s image was from a macadamia tree! A quick check with wikipedia, alas, revealed that the Macadamia genus is native only to eastern Australia, New Caledonia, and Indonesia Sulawesi. A further check at the Trees, Shrubs, and Palms of Panama site assured me that we have no macadamia trees growing wild here.

Proteaceae

However, by now I was confident that I had the Family to which my tree belonged – it is the Proteaceae. Linneaus named this family after Proteus, the Greek who was renowned for his ability to change shape (wiktionary). The family is so variable, in fact, that it is said to be “…impossible to provide a simple, diagnostic identification key for the family, although individual genera may be easily identified” (wikipedia).

The Proteaceae family is found mostly in the Southern Hemisphere and especially in Australia and South Africa. There are two reasons for this distribution – one is plate tectonics and the other is seed type.

Proteaceae and Gondwana of Plate Tectonics Fame

A great land mass, a supercontinent, originated in the Southern Hemisphere about 500-550 million years ago. Geologists call it Gondwana and it included present-day Antarctica, South America, Africa, Madagascar, Australia-New Guinea, and New Zealand as well as Arabia and the Indian subcontinent from the Northern Hemisphere (wikipedia). Species of Proteaceae grew in Gondwana. When the massive supercontinent began to break up through plate tectonics processes about 100 million years ago, species of Proteaceae were isolated on different land masses and began to develop new characteristics in response to the new conditions (Australian Museum Online Fact Sheets).

So it is that the macadamia species evolved in what is now Australia, and other Proteaceae species evolved in South America, South Africa and elsewhere in the Southern Hemisphere.

Proteaceae’s seed types

Once the macadamia had evolved in Australia, it was not dispersed to other continents because of the seed types of Proteaceae. None of the species have “…seeds that can be carried on the plumage of migratory birds or blown across ocean gaps” (Australian Museum Online Fact Sheets). As a result, most Proteaceae species are endemic or native to only one area or continent.

Proteaceae’s weird roots

Many of us in the Northern Hemisphere are used to reading about the root systems of plants forming symbiotic relationships with microscopic fungi to assist in taking nutrients up from the soil. Species in Proteaceae do not do that. Instead, many of them produce masses of short lateral roots in the leaf litter. These roots, known as proteoid or cluster roots, last only during the growth season and then shrivel at the end of the season. The roots makes the plants intolerant of fertilization and, although they help absorb nutrients, especially phosphorus, from another source when the soil is poor, it makes the plants vulnerable to dieback from a water mold that occurs in leaf litter (wikipedia).

How to Recognize a Member of the Proteaceae Family

Once I knew I had a member of the Proteaceae Family, I went to Gentry’s book and found a simple description that matched nearly every characteristic I had noted on that first day.

• Typically found at the edge of montane cloud forests but also scattered in lowland forests. (Check – lowland forest.)
• Coriaceous (leathery) leaves. (Check – okay, I can call these stiff leaves leathery after all.)
• Most have long petioles. (Check – see illustration above.)
• Petioles more or less thickened at base (Check – see illustration below).

Neotropical Proteaceae

Of the approximately 80 genera of Proteaceae, most, as has been noted, are found in Australia and South Africa. Only five are found in the Neotropics (the New World, or Western Hemisphere, tropics) (Gentry and Maas & Westra). This made finding the right genus for my tree considerably easier than it might otherwise have been.

The Genus Roupala

Further, the very next sentence in Gentry’s description of the family Proteaceae suggested which genus I might have:

• The only genus widespread in the lowland forest is Roupala.

And, even better, Roupala is easy to recognize by the

• odor of wood and slash – that of poor quality or slightly spoiled canned beef. The other lowland genus lacks this odor.

But, further,

• Roupala has pinnately compound juvenile leaves and simple mature leaves in some species.

Talk about Protean! I’m used to thinking that if I can figure out whether the leaves are either compound or simple that I will have gone a little ways toward learning what family I have in hand. I elaborated a little on this when writing about the Living Fence (look about halfway down the post). But here is a species that can have both compound leaves and simple leaves on the same tree, depending on its age.

I knew I had a mature tree with simple leaves. I wondered whether there were any juvenile trees in the area so I could look at those leaves.

The species montana

I decided to check my wonderful book, Trees and Shrubs of Panama, which has all the plants arranged by family. And there it was, clear as a bell. Roupala montana, known locally as carne asada – Spanish for “grilled meat.” The author says the common name is because of the color of the fresh cut wood, but I wonder if the odor isn’t also part of the reason for the name. Then I remembered that when we conducted a Bioblitz on this property last April, my Panamanian friends identified one of the young trees as carne asa.I ran out immediately and found the young tree, and, yes, it had compound leaves and the edges were toothed.

 

So it was all falling into place.

The only remaining question was whether Roupala montana would produce a macadamia-like fruit.Alas, the answer is no. These fruits may look like they’re going to produce nuts, but they won’t. The fruits are follicles that will release oval, winged seeds that will germinate at the beginning of the wet season (Fournier – a pdf file).

 

Instead, our macadamia relative is a tree known for its peculiar odor. It does have its uses, though. The young branches are used as yard sweepers and the wood is used for fence posts and to construct the open air huts known as bohios (Carrasquilla). And I, for one, will always look at those bottle-brush inflorescences when they appear and think of macadamias, of Gondwana, and of the weird roots of the tree.