Vascular Plants of Williamson County

Oenothera macrocarpa subsp. macrocarpa [Onagraceae]
fluttermill, missouri primrose

Oenothera macrocarpa Nutt. subsp. macrocarpa, fluttermill, missouri primrose. Perennial herb, not rosetted, several–stemmed at base, spreading to ascending, in range to 35 cm tall; shoots with only cauline leaves, short–strigose.

Stems

Stems cylindric, purple–red, short–strigose with upward–pointing hairs.

Leaves

Leaves helically alternate, simple, petiolate, without stipules; petiole indistinct from blade, hemicylindric lacking green wings, to 6 mm long, pale green, densely short–strigose with upward–pointing hairs; blade narrowly elliptic or elliptic to narrowly lanceolate or linear–lanceolate, in range < 50—115 × (3—)7—18 mm, long–tapered at base, entire to subentire or inconspicuously short–dentate on margins, acute at tip, pinnately veined with midrib raised but especially on lower surface, bright green and sparsely short–strigose.

Inflorescence

Inflorescence leafy raceme, terminal, of helically alternate, axillary flowers, having 1 flower open per day in an ascending order along the rachis, short–strigose like shoot; pedicel stout, to 4 × 2.5—2.8 mm, bending to orient flower upward, densely short–strigose with upward–pointing hairs.

Flower

Flower bisexual, radial, 70—82 mm across, lightly scented; hypanthium above ovary, forming a long floral tube, tube cylindric, 60—133 mm long, 3—3.5 mm most of length and somewhat flared at orifice, whitish to pinkish aging darker when wilted, 8–striped (pale strawberry) along most of length, flared to 5 mm wide at top, nectary at base of hypanthium surrounding style base, thickening 4+ mm long (hypanthium 4 mm wide), green, producing copious thin nectar; sepals 4, in bud erect and narrowly lanceoloid (not 4–sided), light yellow–green, at flower opening remaining partially fused as a unit when they split from pressure of expanding petals along 1 suture line base to tip 4, the unit at anthesis reflexed (inside out), having 4 sepals splitting upward but still fused above midpoint 15—20 from tip but free 2.5—4 mm at tips, greenish but red–purple and short–strigose at tips, exposed (inner) surface glabrous, back (outer) surface densely short–strigose; petals 4, twisted in bud, at pollination widely spreading, broadly obovate, 43—53 × 45—64 mm, light yellow but greenish at thickened base and along principal veins on lower surface, folded along midline, irregularly low–toothed on out margin often having an acute tooth to 2 mm long at end of fold (sometimes in shallow notch), with veins radiating from base, glabrous, withering during midday and aging reddish to red–orange; stamens 8 in 1 whorl, free, arising from rim of hypanthium; filaments long–exserted, cylindric, ca. 20 mm long, yellow, short–tapered to point at top, glabrous; anthers versatile, dithecal, 13.5—14 mm long, pale light yellow, longitudinally dehiscent (before petals spreading); pollen pale yellow, copious, pollen grains triangular (permanently united tetrads), connected with minute threads (viscin threads); pistil 1, exserted above anthers; ovary inferior, strongly 4–winged and obovate to broadly elliptic in outline, 13—21 × 4.5—8 mm, green, densely short–strigose, 4–chambered, each chamber with many ovules; style cylindric, ca. 50 mm > hypanthium + stigmatic lobes, 0.35 mm diameter at base and white with hypanthium, 0.7 mm diameter exserted and light yellow to light yellow–green (above stamens); lobes 4, initially erect at pollination becoming widely spreading, fingerlike, 4 × 0.7 mm, yellow–green, wet, papillate.

Fruit

Fruit capsule, loculicidal, dehiscent by 4 valves along each wing splitting lengthwise top downward ca. 1/4 length (seeds exiting through top opening as fruit dispersed by wind), many–seeded, strongly 4–winged, 45—65 × 35—50 mm, tannish, wings 90° apart and ⊥ to fruit axis, to 22 mm wide, tough, papery; pedicel persistent on bottom, fused portion of fruit.

Seed

Seed irregularly obovoid with 2 wings from midpoint, overall 4—5 mm long, seed body 3.5—4 × 1.6—2.1 mm, brown, coarsely wrinkled and somewhat corky, wings papery, ca. 1 mm wide, brown, toothed.

A. C. Gibson