Oenothera riparia |
Oenothera linifolia |
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threadleaf evening-primrose, threadleaf sundrop |
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Habit | Herbs perennial, sparsely strigillose, becoming glabrate distally, usually also glandular puberulent distally; from a somewhat fleshy rootstock, forming adventitious roots where submerged. | Herbs annual, caulescent, strigillose or glabrous, also often glandular puberulent, especially distally; from a sparsely branched taproot. |
Stems | erect or ascending, usually many-branched throughout, proximal branches often somewhat spongy, 50–120 cm. |
unbranched or with many ascending branches arising near base, erect, 10–50 cm. |
Leaves | in a basal rosette and cauline, softly succulent, 4–13.5 × 0.8–2.1 cm, petiole 0–1.5 cm, blade lanceolate to elliptic-lanceolate, margins remotely denticulate. |
in a basal rosette and cauline, basal 1–2(–4) × 0.2–0.6 cm, petiole 0.2–1(–1.5) cm, blade ovate to obovate or narrowly elliptic; cauline 1–4 × less than 0.1 cm, sessile, blade linear or filiform. |
Inflorescences | erect, flowers in axils of distalmost few nodes. |
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Flowers | opening near sunrise; buds with free tips 0.5–2(–5) mm, erect to spreading; floral tube 14–20 mm; sepals 20–30 mm; petals bright yellow, fading pale pink or lavender, 16–27 mm; filaments 10–15 mm, anthers 7–8 mm, pollen 85–100% fertile; style 15–30 mm, stigma exserted beyond anthers at anthesis. |
usually 1–3 opening per day near sunrise; buds without free tips; sepals 1.5–2 mm; petals bright yellow, fading pink, obcordate to obovate, 3–5(–7) mm; filaments 1–2 mm, anthers 0.5–1 mm; style 1–2 mm, stigma surrounded by anthers at anthesis. |
Capsules | oblong-clavate to oblong-ellipsoid, 4-angled or 4-winged, and wings 0.1–0.2 mm, 7–15 × 4–6 mm, stipe 2–5 mm; sessile. |
ellipsoid-rhombic to subglobose, 4-angled, 4–6(–10) × 1.5–3 mm, stipe 0–4 mm, valve midrib raised at distal end, indehiscent or tardily dehiscent distally; sessile. |
Seeds | 0.8 × 0.4 mm. |
clustered in each locule, ovoid, surface minutely papillose, 1 × 0.5 mm. |
2n | = 56. |
= 14. |
Oenothera riparia |
Oenothera linifolia |
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Phenology | Flowering May–Jul. | Flowering Apr–Jun(–Aug). |
Habitat | Isolated colonies in or at edge of water in marshes or slow-running rivers, apparently with at least some tidal influence. | Prairies, open woodlands, open rocky and sandy sites, roadsides. |
Elevation | 0–10 m. (0–0 ft.) | 0–400 m. (0–1300 ft.) |
Distribution |
GA; NC; SC; VA |
AL; AR; FL; GA; IL; KS; KY; LA; MO; MS; NC; OK; SC; TN; TX
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Discussion | Oenothera riparia has not been accepted as a distinct species for a long time. The conservative approach used by G. B. Straley (1977) is here followed in recognizing a broadly delimited O. fruticosa, except that the very distinctive coastal tidal-freshwater semi-aquatic octoploid populations (Straley 1982) are recognized as O. riparia. Plants of these coastal populations, which occur from southern Virginia to North Carolina, are more robust, more branched, and less pubescent than those of the two subspecies of O. fruticosa, and have slightly succulent leaves and more prominent adventitious roots (Straley 1982; D. Boufford, pers. comm.). Further field studies and cytological analyses are needed to fully understand the geographical and ecological limits of O. riparia and confirm that it is strictly an octoploid species. K. N. Krakos et al. (2014) determined that Oenothera riparia is self-incompatible and is pollinated by bees (Bombus, Lassioglossum, Megachile, Parallelia, Xylocopa, and Zale). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Kneiffia linearifolia Spach (1835) is an illegitimate name based on Oenothera linifolia. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 10. | FNA vol. 10. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Kneiffia riparia, O. tetragona var. riparia | Kneiffia linifolia, O. linifolia var. glandulosa, Peniophyllum linifolium |
Name authority | Nuttall: Gen. N. Amer. Pl. 1: 247. (1818) | Nuttall: J. Acad. Nat. Sci. Philadelphia 2: 120. (1821) |
Web links |