Sea-Oats

Uniola paniculata

Poaceae, the Grass Family

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Not many plants out-beauty sea-oats with its fancy flat spikelets aflutter in the ocean breeze.  Location location location. Despite its conspicuousness, and its value for stabilizing coastal dunes naturally or via cultivation, the species has mysteries.  And it is not really an oat.

Sea-oats. All photos today by John Bradford.

One mystery is, given that Uniola be cultivated inland, why in the wild is the grass almost always restricted to ocean dune, from the high water line to the windward faces or crests of  dunes?  Inland from those places, it disappears abruptly.

One answer is probably competition.   Sea-oats are so specialized for competing on ocean-facing dunes with salt, intense drying, blazing sun, stingy nutrients, relentless abrasive wind, storms, and shifting sands, it may not compete effectively elsewhere.  Fun fact: the roots reportedly can go down 40 feet.

Sea-oats spikelet. Does it contain seeds?

Another sea-oats mystery is reproduction and dispersal.  It makes seeds, but in some places few to none, and often makes empty spikelets.   And when there are seeds, wild mice and other creatures gobble them up.   The big flat spikelets probably blow across the sand to prevent loose seeds from premature burial at the base of the mother plant.    The seed production is influenced by environmental conditions, being correlated with distance from the briny deep.  A big creepy rhizome system is a safeguard from waves and wind, and rhizome segments exposed by shifting sands break free, drift away, and resume existence on new shores.  This ability has served for planting sea-oats where its presence is desired.

Bitter panicum spikelets

Sea-oats has a frenemy called bitter panicum (Panicum amarum).  The two big grasses frequently occur together and have similar seashore distributions up the Eastern Seaboard and down around the Gulf of Mexico.  They are often more or less intermixed on the same beach sites, which raises the question of what ecological differences separate them?   There are some hints of ecological differentiation.   Bitter panicum has broader tastes:  marginally wider range, some “inland” presence (not much),  and less restriction to the windward faces and tops of dunes as sea-oats.  

Bitter panicum

Seems maybe bitter panicum is a little better at competing outside of the narrow sea-oats comfort zone, and sea-oats just a little better at competing in its special place.   They have subtly different nutritional characteristics, and probably have different fungal root associates.   Sea-oats is especially intolerant of waterlogged sand in contrast with bitter panicum extending into swales between dunes and into soggy marshy places.  Bitter panicum is a teeny bit more of a generalist and the “oats” a wee bit more specialist. But then again, the interactions between the two have never been studied so far as I can tell.