Sophora tomentosa

Fabaceae

Every South Florida gardener landscaping with native species* soon encounters the pretty legume shrub necklace pod*, with bright yellow pea-type flowers and pods resembling the snake who ate oranges.

Not a path I’m going to follow, but some readers may be interested in the complex bioactive chemistry and ancient to modern medicinal roles for the genus Sophora, having about 70 species around the world.    All that is easily Googled, and for now set aside.

What’s more interesting is how Sophora tomentosa achieved its global transoceanic distribution.    Around the world, its favored habitats are salty shores, such as beach dunes and other tough habitats adjacent to the sea from Florida to Africa, Japan, and Australia.    In order to colonize new shores as a lonesome castaway (with no pollination partner),  in addition to normal insect pollination, it also has self-pollination as well as cloning requiring no pollination at all.  Reproduction is assured, no matter where a seed washes up and grows.

The seeds are within indestructible lifeboats.  The fruit segments break apart, each segment containing one seed.  The outer layers of the fruit segment surrounding the seed are thick, tougher than armor, and presumably buoyant.  (Also, the seed itself has a small airspace between its two seed leaves.)  When the pod segment the seed within falls in saltwater, or when the tides and waves lift them from the maritime sands, off they go to repopulate seashores around the world!    The longest-recorded saltwater float time followed by germination is 104 days. (Perhaps much longer occurs… 104 days sounds like somebody said, “okay, enough is enough, stop the experiment and see if they sprout.”) 

You can find sprouted necklace pod segments in beach debris.    Do they sprout in the drink and hit the shore already germinated?   Possible,  but my guess, no.  Do the segment-seed units somehow “sense” coming ashore?    Nobody has ever determined that, but I’m betting on it.   There have been some experiments involving S. tomentosa germination, but not asking the interesting question, “what wakes up the seeds on the beach after a long ocean float trip?”   Maybe freshwater rain soaking in?  Microbes and fungi able to grow on shore but not in the ocean?  Or, as tree expert Ray Caranci speculated in conversation yesterday, maybe going from the stable ocean temperatures to fluctuating extremes on land?  

Could the answer merely be wave action scraping the little travelers on the sand?  Like most legume seeds, artificially damaging the seedcoat…”scarification”…does boost germination, but a problem with that explanation is that the seed to scrape is encased in that thick pod-segment armor.   Good luck scratching its seed coat.  

I think I see some low-budget experiments to try. First we need a bucket of seawater and 105 days.

*A note on nativity.   There are two formal varieties of S. tomentosa around town.  Variety occidentalis has fuzzy mature leaves, is in the landscaping trade, is reputedly not native to Florida. Variety truncata has unfuzzy mature leaves and is regarded as native.  Given, however, the ocean-current distribution of this worldwide species, I wonder if Mother Nature may be a little more complex than the textbook version.

Happy New Year.