Home & Garden Columns

Green Neighbors: Pretty Good Tree with a Pretty Dumb Name

By Ron Sullivan
Tuesday March 04, 2008
Casaurina in Martin Luther King Jr. Regional Park, by Arrowhead Marsh, Oakland.
By Ron Sullivan
Casaurina in Martin Luther King Jr. Regional Park, by Arrowhead Marsh, Oakland.

Trust the Aussies (“…from the Land Down Under/Where the women something and the men something-else-that-rhymes with ‘under’—maybe ‘blunder’?—but definitely not whatever the women do”) to get all weird about gender issues in the unlikeliest places. They’re blessed with several species of casuarina, a useful and engagingly weird clade of trees, and what do they call them? “She-oak.” And what do they mean by that? Why, “like oak but inferior.”  

Joke, schmoke. We get it, guys; we’re just bored already. 

Not surprisingly, we have casuarinas planted here and there in the Bay Area. Lots of Australian plants thrive here, as we share a “Mediterranean” climate with much of that continent. Casaurinas (the name still in general nursery-trade use) don’t look like oaks; the dumb name is supposedly about how their lumber performs. What they look most like is pines. 

In fact, they look so much like pines that I’ve passed casaurina plantings for years before twigging to what they were. There is a fairly simple way to tell Casaurina cunninghamiana and Allocasuarina verticillata (formerly Casaurina stricta), which as far as I know are the two most common species here, from pines. Look at the branch tips: Pines’ smallest branches’ ends are blunt and rounded; casaurinas’ sweep into a point.  

When you look more closely, you might notice that the leaves, which like pines’ are reduced to needle form, have joints like those of equisetums—the horsetails or scouring rushes that turn up in damp places. They’re not cousins, though.  

The most recent taxonomic sort-out puts casuarinas in the same order as beeches (northern and southern), birches, bayberries, and walnuts. They’re a Gondwana family, from that former supercontinent: fossils have been discovered in New Zealand and South America, where no living species survive. Australia is their center of distribution, with outliers from India to Polynesia. 

As with a lot of plants these days, there’s some confusion about the names of the different species. According to Elizabeth McClintock’s Trees of Golden Gate Park, the casuarinas planted there are C. cunninghamia, the river she-oak of northern and eastern Australia, sometimes misidentified as C. equisetifolia. At least they’re still together in the genus Casuarina, many of whose members such as the former C. stricta were recently split off into Allocasuarina, hence that name change.  

Whatever their maiden names, they’re all of a very old Australian lineage. Around thirty thousand years ago, as that continent became hotter and drier, casuarinas displaced the ancient araurcarias—primitive conifers like the bunya-bunya and the recently discovered wollemi pine. They were part of a whole flora of scleromorphs, drought- and fire-adapted plants with small scaly water-conserving leaves. Later on the casuarinas were pushed aside by the eucalypts. 

Somewhere along the line, the casuarinas formed a symbiotic partnership with a soil bacterium called Frankia. Living in nodules among the roots, Frankia fixes atmospheric nitrogen and makes it available to the host plant—the same kind of arrangement that another microorganism, Rhizobium, has with the peas and their relatives. Other strains of Frankia co-occur with our native ceanothus, mountain mahogany, and alders. 

The bacterial connection may give casuarinas a competitive edge in nutrient-poor environments. Turn them loose in a warm place and they grow like weeds. They’re a huge concern in Florida, where three species—C. equisetifolia, C. cunninghamiana, and C. glauca—thrive in the alkaline, limestone-derived soils. Originally planted as ornamentals, these Australians have overgrown the habitats of endangered American crocodiles, loggerhead turtles, and gopher tortoises. Their roots suck up disproportionate amounts of soil moisture and invade water and sewer lines, and their leaves are toxic to cattle.  

But on their native turf, casuarinas play important ecological and cultural roles. They’re associated with mycorrhizal fungi that provide food—Australian truffles—for small marsupials like bandicoots and potoroos. In this, they resemble one of California’s persistent lineages, as similar “truffles” feed the squirrels in old-growth coastal redwood forests.  

Native Australians favored casuarina wood for spears, processed and ate the red sap that exudes from the trunks, and chewed the young cones for moisture during long desert treks. Tahitians also used the wood for weapons, and considered the trees as reincarnations of warriors those weapons had killed, apparently because, like them, the trees bleed red.  

The wood tends to be red too, which is why some species are called “beefwood.” Come to think of it, a friend of mine told me he’s had main courses of what he calls the Outhouse Steakback that might as well have been lumber; maybe they were piloting a crypto-vegetarian substitute. Or maybe it was an attempt at a high-fiber diet supplement.  

I await indignant correspondence from outraged Aussies. In the meantime I’ll stick to witchetty grubs. Roasted, please, and hold the Vegemite.  



Ron Sullivan is a former professional gardener and arborist. Her “Green Neighbors” column appears every other Tuesday in the Berkeley Daily Planet, alternating with Joe Eaton’s “Wild Neighbors” column. Her “Garden Variety” column appears every Friday in the Planet’s East Bay Home & Real Estate section.