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Smooth Phlox, Marsh Phlox - Phlox glaberrima


Family: Polemoniaceae - Phlox family Genus Common Name: Phlox Native Status: NativeDicot Perennial Herb Leaves:Opposite
Phlox glaberrima - Smooth Phlox, Marsh Phlox.
The Phlox family - Polemoniaceae - is primarily a family of the Americas with about 350 or so species. There are about 70 species in the Phlox genus. Phlox species can be very difficult to differentiate. Not only do several species share similar shapes in both the flower and the leaves, but the color ranges are broad and similar. You have to look at details to differentiate between many of the plants in this genus.

Phlox glaberrima is a species of the central and southeastern United States, from southern Wisconsin south through Oklahoma to Lousiana, and east to the east coast north to Ohio, West Virginia, and Maryland. Many authorities classify the plant as 3 subspecies, ssp. interior being the westernmost, ssp. triflora being more eastern, and ssp. glaberrima being in a subset of the states where triflora is located. Georgia, Kentucky, and Tennessee are the only states where all three subspecies are found. I have found little information on differentiating between the subspecies except that ssp. triflora has basal foliage which overwinters and it flowers earlier than the others; April through June versus June and July for the other subspecies.

Found in:
AL, AR, FL, GA, IL, IN, KY, LA, MD, MO, MS, NC, OH, OK, SC, TN, VA, WI, WV, GS

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Phlox glaberrima

Distribution of Phlox glaberrima in the United States and Canada:
Map unavailable.
Map courtesy of The Biota of North America Program.
Map color key

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Site: The Pocket at Pigeon Mountain, Walker County, GA Date: 2009-May-09Photographer: Gerald C Williamson
Nikon D60f/16
The flowers of Smooth Phlox have 5 reddish-purple to pink petals which are rounded or very slightly notched. A key identifier in Phlox is whether the stamens show at the opening to the corolla tube. Phlox glaberrima is one of those which shows its stamens to us.
Phlox glaberrima

Site: May Prairie State Natural Area, Coffee County, TN Date: 2016-June-01Photographer: Gerald C Williamson
Nikon D7000
As with all Phlox, the flower has a narrow corolla tube ending abruptly with the petals/lobes at spreading approximately 90-degrees to the tube (salverform). The bell-shaped calyx has narrow sepals which have a distinct midrib. The sepals of the similar Phlox carolina are wider, and the midrib is less well defined.
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Phlox glaberrima

Site: May Prairie State Natural Area, Coffee County, TN Date: 2016-June-01Photographer: Gerald C Williamson
Nikon D7000
Smooth Phlox grows to 4 feet tall, although it is frequently shorter. It is usually unbranched, or may branch some in the upper part of the plant. The inflorescences are at the top of the stem, terminal or in the axils of the upper leaves. There will be 7 or more leaf nodes below the inflorescence.
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Phlox glaberrima

Site: The Pocket at Pigeon Mountain, Walker County, GA Date: 2009-April-25Photographer: Gerald C Williamson
Nikon D60
1/125f/4.5 ISO400
Tamron SP 90MM f/2.8 AF Macro
90mm (135 equiv)
Smooth Phlox flower buds.
Click on the photo for a larger image
Phlox glaberrima

Site: May Prairie State Natural Area, Coffee County, TN Date: 2016-June-01Photographer: Gerald C Williamson
Nikon D7000
The leaves of Phlox glaberrima are opposite and widely spaced on the stems. They are glabrous and entire, shaped lanceolate to nearly linear depending on the subspecies, narrowing to a sharp tip. They may be up to nearly 6 inches long. The upper leaves are sessile; the lower leaves are either sessile or somewhat clasping. The stem is glabrous, green to purplish, and unspotted (similar Phlox carolina usually has a spotted stem.)
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Phlox glaberrima

References used for identification and information:
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Phlox glaberrima initially published on USWildflowers.com 2009-05-15; Updated 2019-01-14

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All content except USDA Plants Database map Copyright Gerald C. Williamson 2024
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Code Update 20230302