Wildflowers of the United States

Michaux's Saxifrage, Mountain Saxifrage - Micranthes petiolaris

Family: Saxifragaceae - Saxifrage family

Genus Common Name: Saxifrage (Alpine Saxifrage)

Native Status: Native

Dicot Perennial Herb

Micranthes petiolaris - Michaux's Saxifrage, Mountain Saxifrage. Based on genetic studies the Saxifraga genus has been split up, with some species remaining in Saxifraga, one being classified in the monotypic genus Cascadia, and 47 species in the new genus Micranthes. There are only eight native North American Saxifraga species remaining in that genus, there are over forty in Micranthes. The easiest diagnostic for Micranthes vs Saxifraga is that the former has only basal leaves (or any cauline leaves may be crowded at the bottom of the stem,) while the latter (Saxifraga) will also have cauline leaves, although they may be very small.

Michaux's Saxifrage, formerly Saxifraga michauxii, is now classified as Micranthes petiolaris (although there is a move afoot that may move it to Hydratica petiolaris.) While many authors still classify this as Saxifraga michauxii, I typically follow the ITIS classification when there is dispute or transition, so am including it as Micranthes petiolaris. I will continue to use Saxifrage as the genus common name so that Saxifraga and Micranthes species will be listed together in the lists ordered by common name, but ITIS lists Micranthes as Alpine Saxifrage.

Michaux's Saxifrage is found on wet rocky places such as rock walls, boulder fields, and seeps in the Appalachian mountains from Maryland south to Georgia. The plants presented here were photographed on a rock wall along the Clingman's Dome parking lot in the Great Smoky Mountains National Park.

Found in:
GA, KY, MD, NC, SC, TN, VA, WV

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Distribution of Micranthes petiolaris in the United States and Canada:

Map courtesy of The Biota of North America Program.
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Site: Clingman's Dome, GSMNP, Swain County, NC Date: 2013-September-23	Photographer: Gerald C. Williamson Nikon D7000 Tamron SP 90MM f/2.8 AF Macro
The blossom of Micranthes petiolaris has 5 white petals which are not necessarily equal in length. If these petals were leaves they would be considered petioled due to their narrow bases. The upper three petals have a pair of yellow marks on them; these marks are absent in the lower two petals. As with all Micranthes species, Michaux's Saxifrage (aka Mountain Saxifrage) has 10 stamens.

Site: Clingman's Dome, GSMNP, Swain County, NC Date: 2013-September-23	Photographer: Gerald C Williamson Nikon D7000 Tamron SP 90MM f/2.8 AF Macro
Michaux's Saxifrage can grow to about 18 inches tall. The flowers are in very open thyrses. I had not run across this term before, so here is a definition of thyrse from TheFreeDictionary: "A dense, paniclelike flower cluster, as of the lilac, in which the lateral branches terminate in cymes."
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Site: Clingman's Dome, GSMNP, Swain County, NC Date: 2013-September-23	Photographer: Gerald C Williamson Nikon D7000
The flowering stem rises from beside the basal leaves rather than from the center of the rosette.
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Site: Clingman's Dome, GSMNP, Swain County, NC Date: 2013-September-23	Photographer: Gerald C Williamson Nikon D7000
The leaves of Micranthes petiolaris are on flattened petioles in a rosette. They are hairy, oblanceolate, and have large teeth.
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Site: Clingman's Dome, GSMNP, Swain County, NC Date: 2013-September-23	Photographer: Gerald C Williamson Nikon D7000
The seeds of Mountain Saxifrage are about one-quarter inch long.
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References used for identification and information:

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Micranthes petiolaris initially published on USWildflowers.com 2013-10-03; Updated 2017-03-02

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Code Update 20230302