Phlox pilosa L. subsp. riparia Wherry, Texas phlox. Perennial herb, 1—several–stemmed at base, having vertical shoots from belowground axis, in range 30 cm tall; shoots pilose on foliage and overall glandular short–hairy, pleasantly fragrant; belowground axis with alternate deltate scales, ± 2 mm.
Stems cylindric, to 2 mm diameter, tough, internodes to 25 mm long.
Leaves opposite decussate, simple, subsessile with pair fused across node, without stipules; basal leaves scalelike and fused across node also subtending 2 lateral branches from node (3—4 basal nodes); of foliage leaves acuminate linear–lanceolate, 11—43 × 3—8 mm, glandular short–hairy with pilose hairs on margins and on lower surface midrib, midrib sunken on upper surface and raised on lower surface.
Inflorescence leafy cume, terminal and later axillary, cyme 3—7–flowered, bracteate, glandular short–hairy; bracts subtending cymes alternate, leaflike, decreasing to bractlet; pedicel to 6 mm long, glandular hairs radiating ⊥ to axis.
Flower bisexual, radial, ca. 20 mm across; calyx 5–lobed, to 15 mm long; tube initially narrowly bell–shaped, 4—5.5 × 2.5 mm, green 1.5 mm at base, above with alternating green and membranous panels; lobes ascending to erect, long–acuminate with awnlike tip, point 1—2 mm long, surfaces glandular short–hairy; corolla 5–lobed, trumpet–shaped (salverform), to 26 mm long, inner surfaces glabrous; tube swollen around ovary at base, whitish and glabrous; throat nearly straight and cylindric narrowly ridged, to 18 mm long, 2 mm diameter at orifice, tubular portion light purple and dishlike upper portion white; lobes widely spreading, ± obovate, ca. 12 × 9 mm, upper surface purple and lower surface light purple, shallowly crenate above midpoint, obtuse at tip; stamens 5, fused to corolla throat most of length and diverging at different levels, the lowest 5 mm from base of corolla, slender approaching anther, ca. 1 mm long, light purple; anthers dorsifixed, dithecal, ± 1.8 mm long, bright yellow, longitudinally dehiscent; pollen bright yellow; nectary disc surrounding base of ovary, 5–lobed, ca. 0.2 mm long, green; pistil 1, at anthesis 4—4.5 mm long (at level of top of calyx tube); ovary superior, ovoid, ca. 2 × 0.8 mm, green, glabrous, 3–chambered, each chamber with 1 ovule attached to center; style green sometimes tinged purple, 3–branched, fork 1 mm from base, the branches stigmatic, ascending.
Fruit capsule, septicidal, 3–valved, 1—3–seeded, ovoid, 3.5—4 mm long, straw–colored.
Seed rhomboid, ca. 2.5 × 1.3 mm, dark amber.
A. C. Gibson