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Spreading Phlox - Phlox diffusa


Family: Polemoniaceae - Phlox family Genus Common Name: Phlox Native Status: NativeDicot Perennial Herb Subshrub
Phlox diffusa - Spreading Phlox. The Phlox family - Polemoniaceae is primarily a family of the Americas. The Phlox genus has 71 species listed in the USDA plants database. Phlox diffusa has four subspecies listed in the USDA Plants Database, implying significant variation within the species. You have to look at details to differentiate between many of the plants in this genus. Phlox diffusa (the species presented here) and Phlox hoodii (Hood's Phlox) are similar plants with overlapping ranges and habitats. Here are a few differences, based on what I've derived from several descriptions:
  • P. hoodii may be more common at lower elevations; P. diffusa at higher elevations.
  • P. hoodii mounds rarely grow higher than 4 inches above the ground; P. diffusa may be as high as 8 inches.
  • P. hoodii is a somewhat later blooming species, usually starting in late spring.
  • P. hoodii is more densely hairy, having woolly stems and leaf bases. The calyx of P. diffusa is smooth; that may not be the case with P. hoodii.
  • P. diffusa will have solitary blossoms at the end of the branchlets. P. hoodii may have up to three flowers at the end of a branchlet.


Found in:
AZ, CA, CO, ID, MT, NE, NM, NV, OR, SD, UT, WA, WY

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Phlox diffusa

Distribution of Phlox diffusa in the United States and Canada:
USDA Plants Distribution Map temporarily unavailable.
Blue=Native; Grey=Introduced

Map from USDA Plants Database:
USDA, NRCS. 2017. The PLANTS Database (http://plants.usda.gov, 27 Jul 2017). National Plant Data Team, Greensboro, NC 27401-4901 USA.

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Site: Custer County, ID Date: 2011-June-13Photographer: Gerald C. Williamson
Nikon D60
Phlox diffusa gets the Spreading Phlox common name because it grows in low mats, and can cover quite a large area.
Phlox diffusa

Site: Custer County, ID Date: 2011-June-11Photographer: Gerald C Williamson
Nikon D60
Spreading Phlox normally has 5 pinkish petals. This example has 6. The stamens are at varying heights in the corolla tube, frequently with one or more slightly exserted.
Click on the photo for a larger image
Phlox diffusa

Site: Custer County, ID Date: 2011-June-11Photographer: Gerald C Williamson
Nikon D60
Sometimes the flowers are entirely white. The plant is branching, with many small branchlets. The flowers are solitary at the end of a branchlet. Plants may grow to 8 inches high.
Click on the photo for a larger image
Phlox diffusa

Site: Custer County, ID Date: 2011-June-11Photographer: Gerald C Williamson
Nikon D60
Phlox diffusa flowers have a smooth calyx. The stems and leaves are hairy but not white-woolly like Phlox hoodii.
Click on the photo for a larger image
Phlox diffusa

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All content except USDA Plants Database map Copyright Gerald C. Williamson 2017
Photographs Copyright owned by the named photographer