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Simpson's primrose-willow

hairy primrose-willow

Habit Herbs sometimes creeping and rooting at nodes, new shoots arising from trailing stems or main caudex, rarely forming stolons. Herbs often with prominent aerenchyma when base submerged, forming stolons 30–250 cm, 2–4 mm thick, creeping in mud or floating in water, sometimes bearing flowers and fruits.
Stems

erect, ascending, decumbent, or prostrate, slightly ridged, well branched, 10–60(–75) cm, glabrous, with raised lines decurrent from leaf axils.

erect, subterete, densely branched, 40–120 cm, densely hirtellous.

Leaves

alternate or proximal pairs opposite;

stipules narrowly ovate-deltate, 0.1–0.3 × 0.1–0.2 mm, succulent;

petiole winged, 0.2–1 cm, blade spatulate or oblanceolate to very narrowly oblanceolate or sublinear, 0.6–1.5(–2) × (0.1–)0.3–0.7(–1.1) cm, base attenuate, margins subentire with hydathodal glands, apex acute or mucronate;

bracts not much reduced.

alternate;

stipules ovate to lanceolate, 0.2–0.25 × 0.1–0.15 mm, usually obscured by pubescence;

stolons: petiole 0.2–0.7 cm, blade obovate or elliptic to orbiculate, 0.6–2 × 0.5–1.1 cm, margins with distinct hydathodal teeth, base attenuate, surfaces densely hirtellous to glabrate;

stems: petiole 0–0.2(–1) cm, blade elliptic or lanceolate-elliptic to very narrowly elliptic, 1.5–8(–10) × 0.3–1.2(–1.4) cm, base cuneate or attenuate, margins entire with obscure hydathodal glands, apex acute or narrowly acute, surfaces ± densely hirtellous, leaves on branches much reduced;

bracts much reduced.

Inflorescences

open, leafy spikes or racemes, flowers solitary in leaf axils;

bracteoles attached in opposite pairs near base of ovary, lanceolate-elliptic, 0.9–1.5(–2.5) × 0.4–0.9 mm, swollen at base, apex acuminate.

usually congested, leafy spikes or racemes, flowers solitary in distal leaf axils;

bracteoles attached 1–2.2 mm distal to base of ovary, linear-lanceolate or narrowly elliptic, 3–6.5(–7.2)× 0.3–1.5(–1.7) mm, apex acuminate, surfaces hirtellous.

Flowers

sepals ascending, creamy white near base adaxially, ovate-deltate, 1.2–1.8 × 1–2 mm, margins entire, apex narrowly acute or acuminate, surfaces glabrous;

petals 0 or very rare;

filaments nearly translucent, 0.5–0.8 mm, anthers 0.2–0.4 × 0.3–0.4 mm;

pollen shed singly;

ovary obconic, subterete or scarcely 4-angled, 1.2–1.8 × 1.2–2 mm;

nectary disc elevated 0.3–0.4 mm on ovary apex, green, 0.9–1.3 mm diam., distinctly 4-lobed, glabrous;

style pale green, 0.4–0.6 mm, stigma pale yellow, subglobose, 0.2–0.3 × 0.2–0.3 mm, not exserted beyond anthers.

sepals ascending with reflexed tips, pale green abaxially, creamy white adaxially, often tinged with pink or red, ovate-deltate, 3.5–5.5(–6) × 2–4 mm, margins entire, apex elongate-acuminate to subcuspidate, surfaces densely hirtellous;

petals 0;

filaments yellowish, 1.5–2.5 mm, base dilated, anthers 0.6–0.9(–1.3) × 0.5–0.7 mm;

pollen shed in tetrads;

ovary obovoid to cup-shaped, 2.5–4 × 2.5–4 mm;

nectary disc elevated 0.3–0.7 mm on ovary apex, bright yellow, turning black upon drying, 2–3.6 mm diam., indistinctly 4-lobed, densely hirtellous around style base and between lobes;

style cream, 1–2 mm, sparsely to densely hirtellous, especially proximally, stigma capitate, 0.3–0.6 × 0.3–0.6 mm, not exserted beyond anthers.

Capsules

obconic, obscurely 4-angled, 1.5–2.5 × 1.5–3 mm, hard-walled, dehiscent by loculicidal slits, pedicel 0–0.4 mm.

subglobose or, sometimes, oblong-obovoid, subterete or with 4 rounded corners, 3–5 × 3–4.5 mm, hard-walled, irregularly dehiscent, pedicel 0–1 mm.

Seeds

light brown or brown, ellipsoid, 0.5–0.6 × 0.3–0.4 mm, surface cells transversely elongate, glabrous, occasionally covered by minute waxy hairs.

brown, elliptic-oblong or oblong-ovoid, slightly curved on both ends, 0.5–0.7 × 0.3–0.4 mm, surface cells ± isodiametric.

2n

= 48.

= 32.

Ludwigia simpsonii

Ludwigia pilosa

Phenology Flowering Apr–Nov (year-round). Flowering Jun–Sep.
Habitat Sandy, peaty ditches, open pineland swamps, edges of cypress swamps, tidal flats and nearby marshes, limestone sinks. Roadside ditches, marshes, swales in sandy pine flats, edges of pocosins, peaty bogs, low grassy savannas, swamp forests.
Elevation 0–50 m. (0–200 ft.) 0–300 m. (0–1000 ft.)
Distribution
from FNA
FL; MS; West Indies (Cuba, Jamaica)
from FNA
AL; FL; GA; LA; MS; NC; SC; TX; VA
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Discussion

Ludwigia simpsonii is a hexaploid species occurring primarily in Florida, with outlier populations in southern Mississippi, western Cuba, and Jamaica. The species grows frequently in close proximity to L. curtissii; it grows mainly along roadside ditches with other weeds, whereas L. curtissii grows in less disturbed habitats, and the two seldom occur side by side (C. I. Peng 1989). Peng (1988, 1989) suggested that the hexaploid (2n = 48) L. simpsonii and the diploid (2n = 16) L. microcarpa gave rise to L. curtissii, the only octoploid (2n = 64) in sect. Isnardia.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

The distribution of Ludwigia pilosa is nearly continuous along the Atlantic and Gulf coastal plains, from extreme southeastern Virginia to northern Florida, and west to Louisiana and southeastern Texas. Disjunct populations occur in northern Alabama and central North Carolina.

Ludwigia pilosa is easily distinguished from most others in sect. Isnardia by being densely hirtellous throughout. Its showy sepals and nectary disc attract multiple insect visitors including ants, bumblebees, honeybees, moths, and wasps (C. I. Peng 1989).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 10. FNA vol. 10.
Parent taxa Onagraceae > subfam. Ludwigioideae > Ludwigia > sect. Isnardia Onagraceae > subfam. Ludwigioideae > Ludwigia > sect. Isnardia
Sibling taxa
L. alata, L. alternifolia, L. arcuata, L. bonariensis, L. brevipes, L. curtissii, L. decurrens, L. erecta, L. glandulosa, L. grandiflora, L. hexapetala, L. hirtella, L. lanceolata, L. leptocarpa, L. linearis, L. linifolia, L. maritima, L. microcarpa, L. octovalvis, L. palustris, L. peploides, L. peruviana, L. pilosa, L. polycarpa, L. ravenii, L. repens, L. spathulata, L. sphaerocarpa, L. suffruticosa, L. virgata
L. alata, L. alternifolia, L. arcuata, L. bonariensis, L. brevipes, L. curtissii, L. decurrens, L. erecta, L. glandulosa, L. grandiflora, L. hexapetala, L. hirtella, L. lanceolata, L. leptocarpa, L. linearis, L. linifolia, L. maritima, L. microcarpa, L. octovalvis, L. palustris, L. peploides, L. peruviana, L. polycarpa, L. ravenii, L. repens, L. simpsonii, L. spathulata, L. sphaerocarpa, L. suffruticosa, L. virgata
Synonyms L. cubensis, L. curtissii var. simpsonii Isnardia mollis, I. pilosa, L. hirsuta, L. mollis, L. rudis
Name authority Chapman: Fl. South. U.S. ed. 2 repr. 2, 685. (1892) — (as simpsoni) Walter: Fl. Carol., 89. (1788)
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