Foamflowers in Maryland and Virginia
iNaturalist recognizes five species of Foamflowers (Tiarella) in eastern North America, but in Maryland and Virginia, there are just two: Tiarella stolonifera and Tiarella cordifolia sensu stricto. The ranges of the two species are immediately adjacent along the Blue Ridge Mountains in western Maryland and western Virginia. Tiarella stolonifera is widely distributed to the north, south, and west of the Blue Ridge while Tiarella cordifolia is confined to the piedmont and upper coastal plain to the east.
Distribution of Tiarella in Maryland counties:
- Tiarella stolonifera: Allegany, Garrett, Harford, Washington
- Tiarella cordifolia sensu stricto: Charles, Montgomery, Prince George’s
Distribution of Tiarella in Virginia counties:
- Tiarella stolonifera: Bath, Bland, Buchanan, Carroll, Dickenson, Floyd, Giles, Grayson, Highland, Pulaski, Rockbridge, Rockingham, Russell, Scott, Smyth, Tazewell, Washington, Wise, Wythe
- Tiarella cordifolia sensu stricto: Albemarle, Amelia, Amherst, Appomattox, Arlington, Augusta, Bedford, Botetourt, Brunswick, Buckingham, Campbell, Caroline, Charlotte, Chesterfield, Culpeper, Cumberland, Fairfax, Fauquier, Fluvanna, Franklin, Goochland, Halifax, Henrico, Henry, James City, Lunenburg, Mecklenburg, Nelson, Patrick, Pittsylvania, Powhatan, Prince Edward, Roanoke, Spotsylvania, Stafford, Sussex
Observations of Tiarella stolonifera in Maryland:
- Observations of Tiarella stolonifera in an expected county in Maryland
- Observations of Tiarella stolonifera in an unexpected county in Maryland
Observations of Tiarella cordifolia sensu stricto in Maryland:
- Observations of Tiarella cordifolia in an expected county in Maryland
- Observations of Tiarella cordifolia in an unexpected county in Maryland
Observations of Tiarella stolonifera in Virginia:
- Observations of Tiarella stolonifera in an expected county in Virginia
- Observations of Tiarella stolonifera in an unexpected county in Virginia
Observations of Tiarella cordifolia sensu stricto in Virginia:
- Observations of Tiarella cordifolia in an expected county in Virginia
- Observations of Tiarella cordifolia in an unexpected county in Virginia
Tips for identification of Tiarella species:
Tiarella stolonifera and Tiarella cordifolia are very similar. The only way to distinguish them is to confirm the presence of a stolon. Tiarella stolonifera is capable of producing a stolon but Tiarella cordifolia is not. Unfortunately, the absence of a stolon doesn’t tell you much since stolon production is seasonal. Relatively few iNat observations actually show the presence of a stolon.
For details, including a color-coded range map, see: Nesom, Guy L. (2021). "Taxonomy of Tiarella (Saxifragaceae) in the eastern USA" (PDF). Phytoneuron. 31: 1–61. (A shortened version of Nesom's paper was published by the North Carolina Botanical Garden in 2022.)
For more general information about Tiarella, see: Observing and identifying Foamflowers in eastern North America
Comments
Very helpful. Thank you!
Nice summary!
As I write this, there are just 22 observations of Tiarella stolonifera in an expected county of MD or VA. Likewise there are only 2 observations of Tiarella cordifolia in an expected county. Most observations are at genus level, and I expect it to stay that way since most identifiers feel uncomfortable basing an ID solely on location.
I suspect a lot of folks didn’t know there was a split. I didn’t know I had a bunch of records that had been dropped down to generic level until @trscavo commented on every single one of them. Thanks!
Identifying the species based on location alone won't tell us if the geographical distribution in the paper is correct. Leaving them at genus won't confirm the distribution either, so it seems we're stuck between the proverbial rock-and-a-hard-place.
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