In 1953, Hara provided new combinations for many sectional and species names when he combined Jussiaea L. with Ludwigia L., and at the time, Ludwigia sect. Oligospermum (Micheli) H.Hara was the correct name for one well-defined section. However, subsequent changes to/clarifications of the botanical code have necessitated a change for that name in that now an autonym is treated as having priority over the name or names of the same date and rank that established it. Since Hara’s combination was based on Jussiaea sect. Oligospermum Micheli, the correct name for this section is Ludwigia sect. Jussiaea (L.) Hoch, W.L.Wagner, & P.H.Raven.

Ludwigia , Jussiaea , sect. Oligospermum, nomenclature

The cosmopolitan group of species known since 1953 as Ludwigia sect. Oligospermum is one of the most distinctive in the genus (Raven 1963, Wagner et al. 2007). Among the diplostemonous sections of Ludwigia – which formerly were segregated as the genus Jussiaea L. – this section differs by having woody, subcylindrical capsules with uniseriate seeds firmly embedded in woody pieces of endosperm and pollen released singly rather than as tetrads or polyads. Most species of the section, which grow in warm-temperate to subtropical moist or wet habitats worldwide, are vigorously aquatic and some (L. peploides (Kunth) P.H.Raven, L. hexapetala (Hook. & Arn.) Zardini, H.Y.Gu & P.H.Raven) can be invasive weeds in wetlands and other wet areas, most recently so in California (Wood 2006, Hoch and Grewell 2012). This polyploid section comprises a group of nine highly variable species that includes three diploid species (n = 8), four tetraploid species (n = 16), one hexaploid species (n = 24, L. grandiflora (Michx.) Greuter & Burdet), and one decaploid species (n = 40, L. hexapetala; see also Nesom and Kartesz 2000). Most species in this section have native distributions restricted to the New World, but two species are restricted to the Old World, L. stolonifera (Guill. & Perr.) P.H.Raven throughout Africa and Madagascar, extending to Turkey and Iraq, and L. adscendens (L.) H.Hara across tropical Asia from India to New Guinea, and from southern Japan to northern Australia, and probably naturalized in Madagascar (Raven 1963, Wagner et al. 2007).

While editing the treatment of Ludwigia for the Flora of North America, Jim Zarucchi noticed a problem with the name used for this section, and after consultation with Kanchi Gandhi informed us that a change was necessary. We are grateful to Zarucchi and Gandhi for pointing out this problem for us. We are making this change now so that the correct combination can be available for FNA.

In his treatment for the Flora Brasiliensis (Martius 1875), Micheli divided the genus Jussiaea into three sections: sect. Eujussiaea, sect. Oligospermum, and sect. Macrocarpon. This division of the genus has been widely followed in subsequent treatments. Munz (1942) provided a treatment for New World species of Jussiaea in which he recognized the same three sections, but provided different names for two of them (no change for sect. Macrocarpon Micheli). For sect. Eujussiaea Micheli, he used the new name sect. Myrtocarpus Munz, and for sect. Oligospermum Micheli, he used sect. Eujussiaea Munz. His rationale was that the section that included the type species of the genus had to retain the generic name, and since Hitchcock and Greene (1929) effectively lectotypified Jussiaea with J. repens L. [= Ludwigia adscendens (L.) Hara], he proposed the name sect. Eujussiaea for the section that included J. repens (this lectotypification has been attributed incorrectly in the past to Britton and Brown (1913)).

Hara (1953), following the conclusion by Brenan (1953) and others that Ludwigia, Jussiaea, and Isnardia (a group sometimes segregated) formed a single genus (as Ludwigia, as established by Baillon 1877), recognized the sections in question as Ludwigia sect. Oligospermum (Micheli) H.Hara, sect. Myrtocarpus (Munz) H.Hara, and sect. Macrocarpon (Micheli) H.Hara. He noted that he was “strictly following the Code” (Hara 1953: 290). This treatment was widely accepted, including by Raven (1963) as well as Munz (1965). Most recently Wagner et al. (2007), in a synopsis of Onagraceae, included all three sections as proposed by Hara.

However, changes made to the ICBN in 1981 and retained in subsequent editions (McNeill et al. 2012), specifically as Article 11.6, invalidated part of this treatment. Article 11.6 states that “an autonym is treated as having priority over the name or names of the same date and rank that established it.” So when the transfer of names from Jussiaea to Ludwigia was made, the correct sectional name combination for Jussiaea sect. Oligospermum should have been Ludwigia sect. Jussiaea, since this is the section that includes the type of the genus. Therefore, we make the following change in compliance with the ICBN.

Thanks to Jim Zarucchi for bringing this problem to our attention, and to Kanchi Gandhi for guidance on the nomenclature.