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false loosestrife, large-flower primrose-willow, primrose willow, six petal water primrose, Uruguayan primrose-willow, water primrose

Habit Herbs, subshrubs, or emergent aquatics, adventitious roots sometimes forming a thick mass 10–23 cm at submerged nodes, sometimes woody at base, white pneumatophores 5–10 cm often on submerged stems. Herbs, perennial, subshrubs, or emergent aquatics, creeping, floating, or emergent and ascending, rooting at nodes, when floating often forming spongy, white pneumatophores at nodes, when erect with spongy base.
Stems

floating or creeping and ascending to erect, terete, 20–200(–400) cm, simple to densely branched apically, glabrous (floating) or sparsely to densely villous (emergent), sometimes villous only on inflorescence.

decumbent to erect or ascending, terete, sometimes angled distally.

Leaves

stipules ovate or deltate, 0.7–2 × 0.5–1.1 mm, not succulent, apex subacute, mucronate;

petiole flattened, 0.5–2(–2.5) cm;

blade narrowly oblanceolate, narrowly elliptic, or lanceolate to obovate or spatulate, (1.5–)4.2–10.7(–13.5) × (0.5–)0.8–3 cm, chartaceous, base cuneate or attenuate, margins entire, apex acute to obtuse, rounded or truncate, sometimes mucronate, surfaces not shiny, usually glabrous, sometimes villous on petiole and veins or throughout;

bracts not reduced.

alternate or fascicled.

Inflorescences

emergent stems sometimes in leafy racemes, sometimes reflexed, flowers solitary in leaf axils;

bracteoles obovate to narrowly obovate, 1–1.8 × 0.7–0.8 mm, apex acute or acuminate, attached on distal 1/2 of pedicel or at ovary base.

Flowers

sepals ovate-deltate or lanceolate-deltate, (8–)12–19 × 2–5 mm, chartaceous, margins entire, apex acuminate, surfaces ± densely villous;

petals bright yellow, sometimes with orange base, fan-shaped, (15–)20–30 × (12–)16–25 mm, apex emarginate or mucronate;

stamens 10(or 12), in 2 unequal series, yellow, filaments recurved, shorter ones (1.6–)2.3–5.2 mm, longer ones (3.1–)3.6–7.5 mm, anthers oblong, (1.2–)1.7–4 × 1–1.5 mm;

ovary subcylindric, terete, 10–18 × 2–3 mm, apex ± broadened, glabrous or sparsely to densely villous;

nectary disc slightly raised on ovary apex, yellowish green, 2–4 mm diam., lobed, glabrous or ringed with white hairs;

style yellow, 6–10 mm, glabrous, stigma subcapitate-globose, 0.5–1.5 × 1.5–2.5 mm, often exserted beyond anthers.

5(or 6)-merous;

petals present, yellow [white];

stamens 2 times as many as sepals, [rarely as many as];

pollen shed as monads.

Capsules

cylindric or subclavate, terete, sometimes curved, (12–)16–24(–30)× 2.5–4 mm, with thick woody walls, irregularly and tardily dehiscent, pedicel (9–)13–25(–85) mm.

cylindric, subcylindric, or subclavate, terete, subterete, or obscurely angled, often up-curved, with thick, woody walls, irregularly and tardily dehiscent.

Seeds

embedded in wedge-shaped piece of endocarp, 0.8–1 × 0.8–1 mm.

in 1 row per locule, pendulous and firmly embedded in woody, coherent segment of endocarp, raphe inconspicuous.

2n

= 80.

= 16, 32, 48, 80, 96.

Ludwigia hexapetala

Ludwigia sect. Jussiaea

Phenology Flowering spring–late fall.
Habitat Wet places, along slow-moving rivers, streams, canals, ditches, often growing into main channel as aquatic weed.
Elevation 0–200[–2600] m. (0–700[–8500] ft.)
Distribution
from FNA
AL; AR; CA; FL; GA; KY; LA; MS; NC; NY; OR; PA; SC; TN; WA; Central America (Costa Rica); South America (Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Paraguay, Peru, Uruguay) [Introduced in w Europe (Belgium, France, Spain)]
[WildflowerSearch map]
United States; Mexico; Central America; South America; West Indies; s Asia; Africa [Introduced in Europe, Pacific Islands, Australia]
Discussion

Ludwigia hexapetala (2n = 80) was formerly included with L. grandiflora (2n = 48) in L. uruguayensis (Cambessèdes) H. Hara, and some authors (G. L. Nesom and J. T. Kartesz 2000) still consider them to be a single species. The small but consistent morphological differences and different ploidy levels argue for keeping them distinct at the species level.

Fernald described Jussiaea michauxiana (1944), since he thought that J. grandiflora Michaux (1803) was a homonym (not J. grandiflora Ruíz & Pavon). However, it was later determined that the volume containing the Ruíz & Pavon name was published in 1830 (not 1802) making the name by Michaux valid and legitimate, and the name by Fernald an illegitimate substitution. Plants now known as Ludwigia hexapetala were included in the circumscription of L. uruguayensis (Cambessèdes) H. Hara (based on J. uruguayensis Cambessèdes) by P. H. Raven (1963[1964]) and P. A. Munz (1965).

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

Species 9 (3 in the flora).

This cosmopolitan polyploid section of nine variable species (11 taxa) includes three diploid species (n = 8), four tetraploids (n = 16), one hexaploid [Ludwigia grandiflora, n = 24; P. H. Raven and W. Tai (1979) reported one anomalous count of n = 48], and one decaploid (L. hexapetala, n = 40; see also G. L. Nesom and J. T. Kartesz 2000). One persistent triploid (2n = 24) hybrid, described as L. ×taiwanensis C. I. Peng [L. adscendens (n = 16) × L. peploides subsp. stipulacea (n = 8); Peng 1990] is widespread in southern China and Taiwan. E. Zardini et al. (1991) reported several other natural hybrids.

Most species of sect. Jussiaea have non-naturalized distributions restricted to the New World. Section Jussiaea differs from most diplostemonous sections by releasing its pollen as monads and having woody, subcylindric capsules with uniseriate, firmly embedded seeds. Most species in sect. Jussiaea are vigorously aquatic, and several (including L. peploides, L. hexapetala, and L. grandiflora) can be invasive weeds in wetlands and wet agricultural areas; the latter two, or all three, species have recently become major invasive species in California, particularly in the Russian and Sacramento river drainages and in the San Diego region, in Arizona (especially Gila and Salt rivers), and in Washington (M. Wood 2006; P. C. Hoch and B. J. Grewell 2012).

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

Source FNA vol. 10. FNA vol. 10.
Parent taxa Onagraceae > subfam. Ludwigioideae > Ludwigia > sect. Jussiaea Onagraceae > subfam. Ludwigioideae > Ludwigia
Sibling taxa
L. alata, L. alternifolia, L. arcuata, L. bonariensis, L. brevipes, L. curtissii, L. decurrens, L. erecta, L. glandulosa, L. grandiflora, 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. simpsonii, L. spathulata, L. sphaerocarpa, L. suffruticosa, L. virgata
Subordinate taxa
Synonyms Jussiaeahexapetala hooker, J. repens var. major, L. grandiflora subsp. hexapetala, L. grandiflora var. hexapetala, L. uruguayensis var. major Jussiaea, Gen., Adenola, Cubospermum, Jussiaea section oligospermum, L. section oligospermum, L. section oocarpon, Oocarpon
Name authority (Hooker & Arnott) Zardini, H. Y. Gu & P. H. Raven: Syst. Bot. 16: 243. (1991) (Linnaeus) Baillon: Hist. Pl. 6: 463. (1876)
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