The Systematics and Evolution of Ludwigia Sect. Microcarpium (Onagraceae)

Abstract

Ludwigia sect. Microcarpium, which consists of 14 species distributed mainly in the southeastern United States, is the second-largest section in the genus, the largest being the phylogenetically central sect. Myrtocarpus of South America.Plants of Ludwigia sect. Microcarpium are morphologically diverse; they form a polyploid complex of four diploids, eight tetraploids, two hexaploids, and one octoploid. They are facultatively autogamous herbaceous plants capable of reproducing both sexually and asexually (forming stolons late in the flowering season). Based on extensive crossing experiments as well as field and herbarium studies, the relationships among species of this section have been clarified. Internal genetic barriers between species are nonexistent, and natural hybridization is fairly common. Among the diploid species, L. linifolia and L. linearis have very narrow leaves, petaliferous flowers, and elongate capsules. The two species, however, differ chromosomally by one reciprocal translocation. Y x hybrids between them are vigorous, have ca. 50% stainable pollen, and produce moderate quantities of viable seeds. Ludwigia stricta, the Cuban endemic, is apparently most closely allied to L. linifolia, based on morphological evidence, but has not yet been studied biosystematically. Ludwigia microcarpa, in contrast, has spatulate-obovate leaves, small, apetalous flowers, and minute obconical capsules. Artificial hybrids between L. microcarpa and either L. linearis or L. linifolia form neither stainable pollen nor seeds; for the most part, the chromosomes of these hybrids do not pair in meiosis. Ludwigia microcarpa probably evolved relatively early from outcrossing ancestors.Although the nine tetraploid members in sect. Microcarpium are sharply distinct morphologically, they can be crossed in any direction in the experimental greenhouse and form fertile F, offspring. Natural hybrids in plants of this group are also fairly common and in some cases blur the boundaries of the species. Somewhat surprisingly, none of the extant diploid species are considered to be direct ancestors of the tetraploids, based on cytogenetic studies.The two hexaploid species, L. alata and L. simpsonii, are not closely related to each other. The affinity of L. alata is definitely with the tetraploid species group. Hybrids between L. alata and any other tetraploid species consistently exhibit a modal configuration of 16 II and 8 I in meiosis. Based on its morphology and the cytology of hybrids involving it, L. alata may have originated through hybridization between a tetraploid species, possibly L. lanceolata, and the diploid L. microcarpa, or populations ancestral to each of these species.Ludwigia simpsonii 9 on the other hand, is closely related to L. curtissii, which is the only octoploid in sect. Microcarpium. The two species are unique in sect. Microcarpium in having loculicidal capsules and, together with the diploid L. microcarpa, in having spatulate-obovate cauline leaves. Cytogenetic and morphological studies suggest that the octopl...

Multi‐locus phylogeny of Ludwigia (Onagraceae): Insights on infra‐ generic relationships and the current classification of the genus

“…1 and 2) affirm earlier morpho logical and molecular phylogenetic studies that strongly sup port Ludwigia as sister to the remaining genera in Onagraceae (Eyde, 1978;Raven, 1988;Bult & Zimmer, 1993;Conti & al., 1993Conti & al., , 1996Hoch & al., 1993;Levin & al., 2003Levin & al., , 2004Berry & al., 2004;Graham, 2005;Berger & al., 2016). Moreover, our results agree with many biosystematic studies that highlighted the highly divergent morphology, anatomy, and cytology of Ludwigia in Onagraceae (Raven, 1963;Carlquist, 1975;Eyde, 1978Eyde, , 1981Eyde, , 1982Raven & Tai, 1979;Praglowski & al., 1983;Tobe & Raven, 1985;Hoch & al., 1993;Peng & al., 2005).…”

“…The inclusive genus Ludwigia has been the subject not only of extensive taxonomic revision (Raven, 1963;Ramamoorthy, 1979;Ramamoorthy & Zardini, 1987;Peng, 1988Peng, , 1989Zardini & al., 1991a;Zardini & Raven, 1992;Peng & al., 2005), but also of comparative analyses in anatomy (Carlquist, 1975(Carlquist, , 1977(Carlquist, , 1982Eyde, 1977Eyde, , 1978Eyde, , 1981Eyde, , 1982Keating, 1982;Peng & Tobe, 1987), palynology (Skvarla & al., 1975(Skvarla & al., , 1978Praglowski & al., 1983;Patel & al., 1984), embryology (Tobe & Raven, 1985, 1986a, cytology (Kurabayashi & al., 1962;Raven & Tai, 1979;Zardini & al., 1991b), reproductive biology (Raven, 1979), and biochemistry (Averett & Raven, 1984;Martin & Dowd, 1986;Averett & al., 1987Averett & al., , 1990. Based on his study of floral anatomy, Eyde (1981) was the first to propose that Ludwigia formed a distinct evolutionary lineage sister to the rest of the family, and his hypothesis has been confirmed by subsequent research (Raven, 1988;Hoch & al., 1993), including molecular studies (Bult & Zimmer, 1993;Conti & al., 1993Conti & al., , 1996Lev...…”

Attraction of the potential biocontrol agent Altica cyanea by volatile compounds of three species of Ludwigia weeds from rice fields

“…Eighty-two species of Ludwigia are divided among 23 sections; 25 of these species are in record of the Old World along with eight sections (Raven, 1963). A mosaic assembly of Ludwigia species has been noted in South America, where 45 of the 82 species are recorded; the family Onagraceae, including the Ludwigia species, appears to have originated in this continent (Ramamoorthy & Zardini, 1987;Peng, 1989). Ludwigia species are considered invasive throughout the world and are a menace to indigenous plant species (Moody, 1989;McGregor et al, 1996;Holm et al, 1997;Tomita et al, 2003;Caton et al, 2010;Chauhan et al, 2011).…”

Recent distribution and phytosociological affiliation of Ludwigia palustris in Slovakia

“…It is also known from the Caucasus (Georgia). Naturalized occurrence has been reported from Hawaii, Australia, and New Zealand [1,9,10].…”