Ludwigia peruviana
Ludwigia sect. Myrtocarpus
Peruvian primrose-willow
usually ridged, rarely succulent, profusely branched, 100–400 cm, usually villous, rarely glabrous, hairs deciduous in age, multicellular, usually tawny.
stipules deciduous, narrowly deltate, 1–1.5 × 0.3–0.5 mm, setaceous;
petiole 0–1.5 cm;
blade usually lanceolate, elliptic or broadly elliptic, sometimes ovate, obovate, or rounded, 2–45 × 1–10 cm, base obtuse or cuneate, rarely asymmetrical, margins entire or gland-toothed, apex usually acute or acuminate, rarely rounded and emarginate, mostly scabrid, membranous or papery, surfaces usually villous, sometimes glabrous;
bracts usually not strongly reduced.
alternate.
leafy racemes, flowers solitary in distal axils;
bracteoles deciduous, usually attached near base or on lower 1/2 of ovary, sometimes on upper pedicel, subtended by reduced, glandlike stipels, ovate or lanceolate to linear, 5–20 × 1–6 mm, apex acute or short-acuminate, surfaces villous.
sepals ovate or ovate-lanceolate, 10–23 × 4–9 mm, apex acute or short-acuminate, sometimes glandular-serrulate;
petals bright yellow, orbiculate or obovate, 10–40 × 10–40 mm, apex rarely emarginate, short-clawed;
stamens 8(or 10) in 2 unequal series, yellow, shorter filaments 1.5–4 mm, longer ones 3.5–5 mm, anthers oblong, 3–6 mm;
ovary obconic, 4- or 5-angled, sometimes subterete, 5–20 × 3–7 mm, narrowed to pedicel, usually densely villous, sometimes glabrous;
nectary disc elevated 0.3–3.2 mm on ovary apex, 4–6 mm diam., 4(or 5)-lobed, sunken, ringed by long, white hairs;
style 1.5–3.5 mm, stigma globose, 1.6–3.5 × 1.8–3.5 mm, usually as long as stamens, rarely exserted beyond them.
4(or 5)[–7]-merous;
petals present, yellow;
stamens 2 times as many as sepals;
pollen shed in polyads.
± sharply 4- or 5-angled, 10–40 × 6–13 mm, thin-walled, irregularly dehiscent, pedicel 5–65 mm.
usually obpyramidal to obconic, rarely subglobose, prominently 4+-angled or subterete, with thin walls, irregularly dehiscent.
brown or reddish brown, oblong, 0.6–0.9 × 0.3–0.4 mm, rounded at ends, with inconspicuous raphe.
in several rows per locule, free, raphe inconspicuous.
= 64, 80, 96, 128.
= 16, 32, 48, 64, 80, 96, 128.
Ludwigia peruviana
Ludwigia sect. Myrtocarpus
Ludwigia peruviana is sometimes cultivated and naturalized, which may account for occurrences in North America and Eurasia. Except in the Amazon basin, where it is known only from few collections in western Amazonia, and in northeastern Brazil, where it is scarce, L. peruviana is common throughout its range, and may behave as a weed, especially along slow-flowing canals and drainage ditches. Ludwigia peruviana is also naturalized at scattered localities in Asia (P. H. Raven 1963[1964]) and around Sydney, Australia. The earliest collection from Asia is labeled “ex horto bot. Bogoriensi Javae misit 1869” (Raven). It also occurs locally in the Nilgiri Mountains of southwest India and in Sri Lanka, as well as in scattered locations in Bangka, Java, Malaysia, and Sumatra from sea level to 1000 m (Raven 1963[1964], 1978).
Jussiaea grandiflora Ruíz & Pavon, a synonym for J. peruviana Linnaeus, appeared in 1830, not in 1802 (P. A. Munz 1942; P. H. Raven 1963[1964]); it is a later homonym of J. grandiflora Michaux (1803), as reported in W. Greuter and T. Raus (1987). Jussiaea hirta (Linnaeus) Swartz is an illegitimate homonym and J. hirta (Linnaeus) Vahl is an illegitimate isonym; both pertain here.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species 19 (1 in the flora).
Section Myrtocarpus, the second largest in the genus, has a center of distribution in southern Brazil, Argentina, and Paraguay; 14 species are restricted to that area and five extend to northern South America [Ludwigia elegans (Cambessèdes) H. Hara], to Central America and southern Mexico [L. caparosa (Cambessèdes) H. Hara, L. nervosa (Poiret) H. Hara, and L. rigida (Miquel) Sandwith], or to the Caribbean and the southern United States [L. peruviana (Linnaeus) H. Hara]. Ludwigia peruviana is naturalized in scattered localities in Asia and Australia (P. H. Raven 1963[1964]; T. P. Ramamoorthy and E. Zardini 1987). South America has been proposed to be the center of origin for Onagraceae and for Ludwigia (Raven 1963[1964], 1988). R. H. Eyde (1977, 1979, 1981) and Raven (1963[1964]) suggested that sect. Myrtocarpus includes species with the most generalized (plesiomorphic) morphology in Ludwigia; the section also includes at least five self-incompatible species (Ramamoorthy and Zardini). Most species outcross; only two are autogamous (L. hassleriana, L. tomentosa). Section Myrtocarpus comprises a polyploid complex consisting of one diploid (L. nervosa,n = 8), four tetraploids (n = 16), five hexaploids (n = 24), five octoploids (n = 32), one decaploid (L. caparosa, n = 40), and one multiploid (L. peruviana, n = 32, 40, 48, 64; Ramamoorthy and Zardini). The chromosome numbers of L. burchellii (Micheli) H. Hara and L. rigida are unknown.
P. A. Munz (1965) included nine species from sect. Myrtocarpus in his treatment for the North American Flora, but the circumscription of the section has changed (Munz 1944; T. P. Ramamoorthy and E. Zardini 1987) and his geographical definition included the West Indies and parts of Mexico/Central America; only Ludwigia peruviana is included in this treatment. Of the other species he included, L. foliobracteolata (Munz) H. Hara, L. nervosa, and L. rigida [as L. lithospermifolia (Kunth) H. Hara] remain in sect. Myrtocarpus and have not been reported in the flora area. The other five species are now placed in other sections: L. latifolia (Bentham) H. Hara (sect. Tectiflora Ramamoorthy), L. erecta (Linnaeus) H. Hara and L. decurrens Walter (sect. Pterocaulon Ramamoorthy), L. inclinata (Linnaeus f.) M. Gómez (sect. Heterophylla Ramamoorthy), and L. sedoides (Humboldt & Bonpland) H. Hara (sect. Humboldtia Ramamoorthy); of those, only L. decurrens and L. erecta occur in the flora area. The classification of this large Myrtocarpus complex was not supported by molecular analysis (Liu S. H. et al. 2017), but any revision must await more complete taxon sampling and better resolution.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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