Snow Trillium in Ohio

Trillium nivale on limestone talus slope in Southwest Ohio.

Snow trillium (Trillium nivale) is one our most early, most small, and most secret spring wildflowers in Ohio. It grows only on thin alkaline soil around rivers, most times in forests but sometimes around the Scioto River in open areas, and always it grows over Silurian limestone or dolomite bedrock or gravel.  The above picture not exaggerate the size, it is really that small when it blooms.

T. nivale distribution, from "Snow Trillium in Ohio", R.L. Stuckey, 1976.

If you look at the above map from Stuckey, 1976, you can see the distribution is wide and scattered in Southwest Ohio, but there are only two sites in the East part of the state, in Jefferson county. These are on isolated limestone outcrops, and these are close to other populations on outcrops in western Pennsylvania. Eastern Ohio has most sandstone and shale bedrock, so happen you will never see snow trillium in those areas. It is a very strong calcicole, it never crosses the shale/limestone boundary line on the map. In western Ohio, most bedrock is Silurian mix of limestone, dolomite, and some shale. But over these in most areas there is many feet glacial till, except in river valleys where water cut down through the till and expose the bedrock. I talk a little bit about this in my post about Chinquapin Oak.

Brassfield limestone cliffs on Little Miami River

Because the rivers cut through and expose the bedrock, for snow trillium they are corridors. Ants disperse the seeds through the limestone talus, and where there is not really a lot competition, the snow trillium make colonies. But there are two more important lines on the Ohio map. One line, through the southeast part of the state, is the glacial maximum. All areas above that line had glaciers sometime in the past 300 thousand years. This means Dayton and other areas in southwest Ohio were covered with hundreds feet ice and the land under destroyed. No wildflower can live there, so happen the snow trillium must move north from refugia after the glaciers left. The only areas with snow trillium and alkaline bedrock in the not-glaciated area are in Adams county. Chalet Nivale in Arc of Appalachia is a good example. In the paper with the above map, Stuckey thought that the snow trilium moved from refugia in Adams county north into the Miami and Little Miami and Scioto River valleys. And I think it seem right they move along river valleys where bedrock is exposed.

Cedarville Dolomite cliffs on Massie Creek Gorge

There is one more thing about the Ohio distribution map. You never really see snow trillium in talus around Cincinnati. The bedrock there (in black) is Ordovician, not Silurian. And many the bedrock is limestone [Stuckey says it is dolomite, but the strata profile below show limestone, so happen I don't know why he think that]. Snow trillium prefer limestone, but it will also grow on dolomite soils. Example is Massie Creek Gorge, and the dolomite there is name for the town (Cedarville Dolomite). But you will never find it in Caesar Creek Gorge. Why? Stuckey not guess in that paper, and it is really weird you never find it around Cincinnati.

From "Geology of the Dayton Region in Core and Outcrop", G.A. Schumacher and more, 2012.

If you look at the Silurian limestone and dolomite layers in the above strata map for the Dayton area, you can see that shale layers surround them, but they are still really defined layers. Both the Cedarville Dolomite and the Brassfield Limestone are thick and separate from the shale layers. But if you look at the Ordovician layers around Cincinnati, you can see most limestone/dolomite is mixed with shale, or it is thin layers between shale layers. Shale rock is acidic, and snow trillium will not grow on it. And when shale break apart it become a gray acidic clay, and most times you can think this will cover and cancel the alkaline buffer from the dolomite. Maybe the pH is high enough for mild cacicoles, example Jeffersonia, but it is not alkaline enough for snow trillium.

Waynesville Formation? Ordovician dolomite and shale in Caesar Creek Gorge

 So happen I think this happen. When the glaciers receded, the snow trillium followed the river valleys north into central and southwest Ohio, where Silurian limestone and dolomite was exposed. First this was most the southwest part of Ohio, but over thousands years the rivers cut down through the Silurian layers into the mixed Ordovician shale-dolomite. And with more time the Ordovician valleys widened and the Silurian layers were only on the boundaries. Populations around Cincinnati shifted north and west and east on the boundary and the old populations extirpated because the soil it was not alkaline enough. Now you only see them on and north from the Ordovician boundary.

T. nivale after a little March snow.