Oenothera macrocarpa in Flora of North America @ efloras.org

26. Oenothera macrocarpa Nuttall, Cat. Pl. Upper Louisiana. no. 56. 1813.

Megapterium macrocarpum (Nuttall) R. R. Gates; M. nuttallianum Spach

Herbs caulescent, strigillose or glabrous, sometimes glandular puberulent distally; from a stout taproot, sometimes lateral roots producing adventitious shoots. Stems moderately leafy, (1–)4–40(–60) cm. Leaves cauline, (2.8–)3.7–12.5(–17) × (0.1–)0.4–3(–4.5) cm; petiole (0.4–)1–4(–6) cm; blade linear, lanceolate-elliptic, elliptic to oblanceolate or suborbiculate, margins entire or conspicuously or inconspicuously denticulate or serrulate, sometimes undulate, apex usually acute, sometimes obtuse or retuse (subsp. incana). Flowers usually 1 or 2, rarely more, opening per day near sunset, fading next morning, sometimes (subspp. macrocarpa and oklahomensis) lasting for 2 days, weakly scented; buds with unequal free tips 1–11(–15) mm; floral tube (21–)35–140(–160) mm; sepals (20–)25–65(–75) mm; petals bright yellow, fading orange, reddish orange or mostly unchanged, obovate to very broadly obovate, (17–)25–65(–68) mm, usually with terminal notch and/or tooth, margin sometimes erose; filaments 13–40(–44) mm, anthers 10–24(–25) mm; style (45–)55–192 mm, stigma usually exserted beyond anthers at anthesis. Capsules papery in age, narrowly ellipsoid to lanceoloid, sometimes twisted (subsp. fremontii), winged, wings (2–)10–28(–34) mm wide, body (13–)25–70(–115) × 2–9 mm, dehiscent 1/4–1/3 their length; pedicel 1–12(–25) mm. Seeds numerous, rarely as few as 8, in 1 row per locule, obovoid, (2–)3–5 × 1–2.3 mm.

Subspecies 5 (4 in the flora): c, s United States, n Mexico.

Oenothera macrocarpa is variable and has differentiated extensively in the Great Plains region. Each of the five distinctive subspecies occupies a different geographical and ecological situation. Only subsp. Mexicana W. L. Wagner from Coahuila, Mexico, occurs outside of the flora area. In general, the subspecies are sharply distinct and each is characterized by a number of features, including pubescence, leaf features, flower and floral tube size, and size and morphology of the capsules and seeds. The five entities are treated as subspecies primarily because of their complete interfertility and extensive intergradation in any area of marginal contact. Intermediates are known between subsp. Macrocarpa and subspp. Fremontii and oklahomensis and between subspp. Incana and oklahomensis. There is also some evidence that suggests past hybridization between subspp. Fremontii and incana although there is no present contact between them. All subspecies are self-incompatible.

Oenothera alata Nuttall (1818) is an illegitimate name based on O. macrocarpa and pertains here.

1 Herbs glabrous. (2)

+ Herbs strigillose. (3)

2 (1) Leaf blades usually very broadly elliptic to suborbiculate, rarely oblanceolate or elliptic, 2–4.3 cm wide, margins usually entire, sometimes inconspicuously denticulate, usually flat, sometimes undulate 26b Oenothera macrocarpa subsp. incana (in part)

+ Leaf blades usually elliptic to lanceolate-elliptic, sometimes linear, (0.3–)0.8–2(–3) cm wide, margins usually conspicuously denticulate to serrulate, rarely subentire, usually undulate 26c Oenothera macrocarpa subsp. oklahomensis

3 (1) Bud free tips 1–2(–5) mm; petals (17–)25–33(–37) mm; floral tubes (21–)35–65(–80) mm; capsules often twisted, 13–30(–65) mm, wings 2–5(–9) mm wide 26d Oenothera macrocarpa subsp. fremontii

+ Bud free tips (4–)5–11(–12) mm; petals (25–)31–65(–68) mm; floral tubes (50–)70–140(–160) mm; capsules not twisted, (28–)30–70(–115) mm, wings 10–28(–34) mm wide. (4)

4 (3) Leaves green or younger ones grayish green, moderately strigillose, rarely more densely strigillose, blades often lanceolate-elliptic to broadly elliptic, sometimes linear or lanceolate, 0.4–2.3(–3) cm wide; capsule wings (14–)18–28(–34) mm wide 26a Oenothera macrocarpa subsp. macrocarpa

+ Leaves gray, densely strigillose, blades very broadly elliptic to suborbiculate, rarely oblanceolate or elliptic, 2–4.3 cm wide; capsule wings 10–15(–24) mm wide 26b Oenothera macrocarpa subsp. incana (in part)

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