Ludwigia hexapetala
Onagraceae subfam. ludwigioideae
false loosestrife, large-flower primrose-willow, primrose willow, six petal water primrose, Uruguayan primrose-willow, water primrose
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.
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.
stipules present.
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.
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.
floral tube absent;
sepals (3 or)4 or 5(–7), persistent at ovary apex after dehiscence of other floral parts;
petals yellow or white, rarely absent.
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.
embedded in wedge-shaped piece of endocarp, 0.8–1 × 0.8–1 mm.
= 80.
Ludwigia hexapetala
Onagraceae subfam. ludwigioideae
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.)
Genus 1, species 82 (31 in the flora): North America, Mexico, West Indies, Bermuda, Central America, South America, se Asia, Africa, Indian Ocean Islands, Pacific Islands, Australasia; introduced in Europe, w Asia.
Ludwigioideae were segregated as a distinct subfamily (W. L. Wagner et al. 2007) to reflect the phylogenetic relationship of Ludwigia as sister to other genera of Onagraceae in morphological and molecular analyses (see R. A. Levin et al. 2003, 2004). Ludwigia is distinguished by the absence of a floral tube, persistence of sepals on capsules after other floral parts dehisce, pollen shed in tetrads or polyads (or as monads in some sections, tetrads sometimes found elsewhere in Onagraceae), double ovule vascular supply, uniquely including a central supply (R. H. Eyde 1981), single-celled ovule archesporium (H. Tobe and P. H. Raven 1996), and a base chromosome number of x = 8.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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