Phlox divaricata L.

Blue Phlox

© DETenaglia

Family - Polemoniaceae

Habit - Perennial forb with slender rhizomes. Both vegetative and fertile stems usually present.

Stems - Vegetative stems 1 to several, morphologically distinct from the flowering ones, usually overwintering (the leaves at least partly evergreen), 2-18 cm long, decumbent, rooting at the lower nodes, densely pubescent with short, appressed to curved hairs. Flowering stems ascending to erect, to 45 cm, typically 1-8, with 4-6 nodes, moderately to densely pubescent with curved or crinkled hairs, these often gland-tipped toward the stem tip.

© DETenaglia

Leaves - Opposite, simple, entire, sessile. Leaves of the vegetative stems elliptic, angled to a bluntly or sharply pointed tip, angled at the base, the largest 1.5-5.0 cm long and 10-20 mm wide, the margins usually hairy, the surfaces moderately hairy to nearly glabrous; those of the flowering stems with the blade oblanceolate to elliptic or ovate toward the stem base and mostly angled or tapered at the base, grading to lanceolate toward the stem tip and broadly angled to rounded or truncate at the base, variously rounded to bluntly pointed at the tip, the largest 2.5-5.0 cm long, at least the uppermost hairy along the margins, the surfaces sparsely to densely pubescent with curved or crinkled hairs, sometimes nearly glabrous with age, the hairs often gland-tipped on the uppermost leaves, the secondary veins obscure, pinnate and not forming conspicuous loops.

	Stem and leaves.
© SRTurner

	Three-leaf whorl. These are not uncommon.
© SRTurner

	Leaves of vegetative shoots.
© DETenaglia

Inflorescence - Aggregate of 8-25 flowers appearing as a small, domed panicle. Flower stalks 4-13 mm.

	Inflorescence.
© SRTurner

Flowers - Calyces 6-10 mm long, the lobes slender, each tapered evenly to a short sharp extension of the midnerve, glandular-hairy. Corollas lavender to light purple or pale blue, rarely white, the tube 11-17 mm long, glabrous externally, with a slight constriction 1.5-3.0 mm above the base, the 5 lobes 10-15 mm long and 5-9 mm wide, obovate, rounded at the tips, sometimes with an abrupt, minute point at the very tip. Stamens with the filaments 5-14 mm long, the anthers positioned above the stigma within the tube. Style 0.5-1.5 mm long, the stigmas 1.0-1.5 mm long.

	Buds. The appearance of the tightly rolled corolla is characteristic of Phlox.
© SRTurner

	Calyces and corolla tubes.
© SRTurner

	Corollas. Stamens and style are down inside the corolla tube and not visible at the throat.
© DETenaglia

	Unusual 7-lobed corollas.
© SRTurner

	Calyces.
© DETenaglia

	White variant, which has been called f. candida.
© SRTurner

Fruits - Capsules with 3 seeds, these 2-4 mm long, oblong-ovate to occasionally broadly ellipsoid, slightly flattened, the surface yellowish brown to dark brown, faintly to moderately wrinkled, not becoming sticky when moistened.

	Fruits, in persistent calyces.
© SRTurner

Flowering - April - June.

Habitat - Forests, streambanks, bases of bluffs, roadsides.

Origin - Native to the U.S.

Lookalikes - Other species of Phlox.

Other info. - This is the most common species of Phlox in Missouri, occurring across the state wherever appropriate habitat is present, and also common across the eastern half of the continental U.S. It blooms early, lending one of the first splashes of color to the springtime woodland. It is easily recognized as a species of Phlox by its opposite, sessile leaves and purple flowers with spatulate petals; however, several other species of Phlox have a similar appearance and can easily be confused. Traits which point to this species are hairless corolla tubes, functional parts (stamen and style) which are usually not visible without dissecting the flower, and the presence of vegetative offsets near the main flowering stems. The flowers are usually blue-purple, but pink or white forms are occasionally encountered (see photo above).

The species name divaricata refers to the divaricate (widely diverging) inflorescence habit. The species has been subdivided according to whether the corolla lobes are apically notched (ssp. divaricata, found to the east of Missouri) or not (ssp. laphamii, found in Missouri and in southern states). However, there is extensive intergradation of these entities and many botanists choose not to recognize them.

Photographs taken off Northwood Rd., Platte County, MO., 4-7-00, and near Van Buren, MO., 4-15-01 (DETenaglia); also at Young Conservation Area, Jefferson County, MO, 4-25-2013, 4-12-2017, and 5-4-2018, Greensfelder County Park, St. Louis County, MO, 4-20-2010, and at Valley View Glade Natural Area, Jefferson County, MO, 5-24-2021 (SRTurner).