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The sweet potato is one of the world's most widely consumed crops, yet its evolutionary history is poorly understood. In this paper, we present a comprehensive phylogenetic study of all species closely related to the sweet potato and address several questions pertaining to the sweet potato that remained unanswered. Our research combined genome skimming and target DNA capture to sequence whole chloroplasts and 605 single-copy nuclear regions from 199 specimens representing the sweet potato and all of its crop wild relatives (CWRs). We present strongly supported nuclear and chloroplast phylogenies demonstrating that the sweet potato had an autopolyploid origin and that Ipomoea trifida is its closest relative, confirming that no other extant species were involved in its origin. Phylogenetic analysis of nuclear and chloroplast genomes shows conflicting topologies regarding the monophyly of the sweet potato. The process of chloroplast capture explains these conflicting patterns, showing that I. trifida had a dual role in the origin of the sweet potato, first as its progenitor and second as the species with which the sweet potato introgressed so one of its lineages could capture an I. trifida chloroplast. In addition, we provide evidence that the sweet potato was present in Polynesia in pre-human times. This, together with several other examples of long-distance dispersal in Ipomoea, negates the need to invoke ancient human-mediated transport as an explanation for its presence in Polynesia. These results have important implications for understanding the origin and evolution of a major global food crop and question the existence of pre-Columbian contacts between Polynesia and the American continent.

A monograph of the 425 New World species of Ipomoea is presented. All 425 species are described and information is provided on their ecology and distribution, with citations from all countries from which they are reported. Notes are provided on salient characteristics and taxonomic issues related to individual species. A full synonymy is provided and 272 names are lectotypified. An extensive introduction discusses the delimitation and history of Ipomoea arguing that a broad generic concept is the only rational solution in the light of recent phylogenetic advances. Although no formal infrageneric classification is proposed, attention is drawn to the major clades of the genus and several morphologically well-defined clades are discussed including those traditionally treated under the names Arborescens, Batatas, Pharbitis, Calonyction and Quamoclit, sometimes as distinct genera, subgenera, sections or series. Identification keys are provided on a regional basis including multi-entry keys for the main continental blocks. Six species are described as new, Ipomoea nivea J.R.I. Wood & Scotland from Peru, I. apodiensis J.R.I. Wood & Scotland from Brazil, I. calcicola J.R.I. Wood & Scotland, I. pochutlensis J.R.I. Wood & Scotland, I. zacatecana J.R.I. Wood & Scotland and I. ramulosa J.R.I. Wood & Scotland from Mexico, while var. australis of I. cordatotriloba is raised to specific status as I. australis (O’Donell) J.R.I. Wood & P. Muñoz. New subspecies for I. nitida (subsp. krapovickasii J.R.I. Wood & Scotland) and for I. chenopodiifolia (subsp. bellator J.R.I. Wood & Scotland) are described. The status of previously recognized species and varieties is changed so the following new subspecies are recognized: I. amnicola subsp. chiliantha (Hallier f.) J.R.I. Wood & Scotland, I. chenopodiifolia subsp. signata (House) J.R.I. Wood & Scotland, I. orizabensis subsp. collina (House) J.R.I. Wood & Scotland, I. orizabensis subsp. austromexicana (J.A. McDonald) J.R.I. Wood & Scotland, I. orizabensis subsp. novogaliciana (J.A. McDonald) J.R.I. Wood & Scotland, I. setosa subsp. pavonii (Hallier f.) J.R.I. Wood & Scotland, I. setosa subsp. melanotricha (Brandegee) J.R.I. Wood & Scotland, I. setosa subsp. sepacuitensis (Donn. Sm.) J.R.I. Wood & Scotland, I. ternifolia subsp. leptotoma (Torr.) J.R.I. Wood & Scotland. Ipomoea angustata and I. subincana are treated as var. angustata (Brandegee) J.R.I. Wood & Scotland and var. subincana (Choisy) J.R.I. Wood & Scotland of I. barbatisepala and I. brasiliana respectively. Attention is drawn to a number of hitherto poorly recognized phenomena in the genus including a very large radiation centred on the Parana region of South America and another on the Caribbean Islands, a strong trend towards an amphitropical distribution in the New World, the existence of a relatively large number of species with a pantropical distribution and of many species in different clades with storage roots, most of which have never been evaluated for economic purposes. The treatment is illustrated with over 200 figures composed of line drawings and photographs.

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Studies on the digenean parasites of deep-sea (> 200 m depth) teleosts are reviewed and two case study generic phylogenies are presented based on LSU rDNA and ND1 mtDNA sequences. The phylogeny of the lepocreadiid genus Lepidapedon, the most common deep-sea digenean genus, is not clearly resolved as the two gene trees are not compatible. It can be inferred, however, that the genus has radiated in the deeper waters off the continental shelf, mainly in fishes of the gadiform family Macrouridae. Steringophorus, a fellodistomid genus, is better resolved. In this case a deep-sea radiation is also indicated, but the pattern of host-specificity is not clear, with evidence of much host-switching. Results of studies of the parasites of the macrourid fish Coryphaenoides (Nematonurus) armatus from various depths have reinforced recent views on the lack of zoned depth-related communities in the deep-sea. The diversity of deep-sea digeneans is relatively low with only 18 families (of about 60) reported. Little, or nothing, is known from most deep-sea areas and nothing from trenches and mid-ocean ridge systems.