8. Phlox pilosa L. (downy phlox, prairie phlox)

Pl. 494 c, d; Map 2259

Plants perennial herbs with slender rhizomes. Vegetative stems not produced or, if 1 or a few present, then shorter than but otherwise similar to the flowering ones. Flowering stems typically 1–3, 25–60 cm tall, erect or ascending, with 6–17 nodes, moderately to densely pubescent with multicellular, spreading to curved or crinkled hairs, some or all of these sometimes gland-tipped. Leaves all opposite or the uppermost rarely subopposite, the lowermost (sometimes all of the leaves on vegetative stems) with the blades linear to narrowly elliptic, grading to narrowly lanceolate, lanceolate, or ovate toward the tip, angled or tapered to a sharply pointed tip, tapered to angled, rounded, or shallowly cordate (those toward the stem tip) at the base, those of the largest leaves 7.5–12.5 cm long and 5–20 mm wide, the surfaces glabrous or nearly so (the upper surface shiny), the margins of the lower leaves sometimes slightly rolled under, glabrous, the secondary veins obscure, pinnate and not forming conspicuous loops, the blade narrowly to broadly elliptic, angled or tapered to a sharply pointed tip, angled or tapered at the base (the uppermost sometimes rounded to nearly truncate), the largest 3.5–8.0 cm long and 2–20 mm wide, the margins usually short-hairy (except sometimes on the lowermost leaves), the surfaces sparsely (occasionally on the lowermost leaves) or moderately to densely hairy, the hairs nonglandular or some or all of them gland-tipped, the secondary veins obscure, pinnate and not forming conspicuous loops. Inflorescences with 15–60 flowers, consisting of sometimes spreading or somewhat drooping clusters, the aggregate of clusters sometimes appearing as small, domed panicles. Flower stalks 1–9 mm. Calyces 7–14 mm long, the lobes slender, tapered to sharply pointed tips, glandular- or nonglandular-hairy. Corollas light pink to bright pink, lavender, or light purple, rarely white, the tube 10–16 mm long, usually moderately to densely hairy externally, with a slight constriction 1.5–3.0 mm above the base, the lobes 6–14 mm long and 4–11 mm wide, obovate or less commonly oblanceolate, rounded at the tips, sometimes with an abrupt, short point at the very tip. Stamens with the filaments 4–15 mm long, the anthers positioned above the stigma within the tube (not exserted). Style 0.4–1.0 mm long, the stigmas 0.9–1.6 mm long. 2n=14, 28. April–June.

Scattered to common nearly throughout the state (eastern U.S. west to North Dakota and Texas; Canada, Mexico). Glades, savannas, upland prairies, bottomland forests, mesic to dry upland forests, bases, ledges, and tops of bluffs, margins of sinkhole ponds, banks of streams and rivers, and fens; also pastures, old fields, ditches, railroads, and roadsides.

Phlox pilosa is cultivated occasionally as an ornamental (mainly ssp. pilosa). The species exhibits great morphological variation across its range and several infraspecific entities have been recognized, with three of these (ssp. fulgida, ssp. ozarkana and ssp. pilosa) reported from Missouri. Taxa not occurring in Missouri are narrow in range (two occurring in dry limestone soils of central Texas [one known from adjacent Coahuila], one in quartzitic hills in southwestern Oklahoma, one in a floodplain area in central Illinois, and one in open woods of northwestern Tennessee, western Kentucky and southern Indiana; see C. J. Ferguson [1998]). Variation in ploidy level occurs within P. pilosa (the central Texas taxa are tetraploid; and the existence of both diploid and tetraploid populations of P. pilosa ssp. pilosa, as currently circumscribed, is evidenced by some reports of chromosome counts [Arkansas and Texas; D. M. Smith and Levin, 1967; Levy and Levin, 1974] and by flow cytometry data [Oklahoma and Texas; C.J. Ferguson and L. Worcester, unpublished]), but the species appears to be diploid over most of its range, and polyploidy has not been documented for Missouri populations.

Rare plants of P. pilosa with white corollas have been called f. albiflora MacMill. Within Missouri, P. pilosa ssp. fulgida is well differentiated ecologically and morphologically, but ssp. ozarkana and ssp. pilosa intergrade extensively in the Ozark region. Both of these latter taxa occasionally co-occur with P. divaricata and putative hybrids can occur. Furthermore, some of the variation within P. pilosa ssp. ozarkana may be a result of past hybridization with P. divaricata. Population genetic studies are needed to help address this possibility.