A peer-reviewed open-access journal PhytoKeys 84: 1–104 (2017) A revision of the Solanum elaeagnifolium clade... 1 doi: 10.3897/phytokeys.84.12695 RESEARCH ARTICLE http://phytokeys.pensoft.net Launched to accelerate biodiversity research A revision of the Solanum elaeagnifolium clade (Elaeagnifolium clade; subgenus Leptostemonum, Solanaceae) Sandra Knapp1, Eva Sagona1,2, Anna K.Z. Carbonell3, Franco Chiarini4 1 Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom 2 Orto Botanico Forestale di Abetone, Associazione Ecomuseo della Montagna Pistoese, Palazzo Achilli, Piaz- zetta Achilli n. 7 - 51028 Gavinana, Pistoia (PT), Italy 3 Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, United Kingdom 4 Instituto Multidisciplinario de Biología Vegetal (IMBIV), CONICET-UNC, Universidad Nacional de Córdoba, Córdoba, Argentina Corresponding author: Sandra Knapp ([email protected]) Academic editor: L. Giacomin | Received 13 March 2017 | Accepted 3 July 2017 | Published 7 August 2017 Citation: Knapp S, Sagona E, Carbonell AKZ, Chiarini F (2017) A revision of the Solanum elaeagnifolium clade (Elaeagnifolium clade; subgenus Leptostemonum, Solanaceae). PhytoKeys 84: 1–104. https://doi.org/10.3897/ phytokeys.84.12695 Abstract TheSolanum elaeagnifolium clade (Elaeagnifolium clade) contains five species of small, often rhizomatous, shrubs from deserts and dry forests in North and South America. Members of the clade were previously classified in sections Leprophora, Nycterium and Lathyrocarpum, and were not thought to be closely related. The group is sister to the species-rich monophyletic Old World clade of spiny solanums. The species of the group have an amphitropical distribution, with three species in Mexico and the southwestern United States and three species in Argentina. Solanum elaeagnifolium occurs in both North and South America, and is a noxious invasive weed in dry areas worldwide. Members of the group are highly variable morpho- logically, and this variability has led to much synonymy, particularly in the widespread S. elaeagnifolium. We here review the taxonomic history, morphology, relationships and ecology of these species and provide keys for their identification, descriptions, full synonymy (including designations of lectotypes) and no- menclatural notes. Illustrations, distribution maps and preliminary conservation assessments are provided for all species. Resumen El clado Elaeagnifolium contiene cinco especies arbustivas, usualmente rizomatosas, distribuidas en desi- ertos y bosques secos de Norte y Sudamérica. Previamente, los miembros del clado estuvieron agrupados en las secciones Leprophora, Nycterium y Lathyrocarpum porque se pensaba que no estaban estrechamente Copyright Sandra Knapp et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 2 Sandra Knapp et al. / PhytoKeys 84: 1–104 (2017) relacionados. El grupo es hermano de los Solanum del Viejo Mundo (Old World clade). Las especies del grupo tienen una distribución anfitropical, con tres especies de México y el Suroeste de Estados Unidos y tres especies en Argentina. Solanum elaeagnifolium se encuentra en Norte y Sudamérica, y es conocida como una nociva hierba invasora en áreas secas de todo el mundo. Los miembros de este grupo son alta- mente variables en su morfología, lo cual ha llevado a la existencia de mucha sinonimia, particularmente en S. elaeagnifolium. Aquí revisamos la historia taxonómica, morfología, relaciones y ecología de estas especies; así mismo, proveemos claves para su identificación, descripción, sinonimia completa (incluyendo las designaciones de lectotipos) y notas nomenclaturales. Además proveemos ilustraciones, mapas y eval- uaciones del estado de conservación de las especies. Keywords amphitropical, conservation status, invasive species, lectotypification, Leptostemonum, New World, pre- liminary conservation status, Solanaceae, spiny solanums, weeds Table of contents Introduction ............................................................................................................. 2 Taxonomy and relationships ..................................................................................... 3 Morphology ....................................................................................................... 5 Biology and natural history .............................................................................. 13 Species concepts ............................................................................................... 18 Materials and methods ........................................................................................... 19 Taxonomic treatment ............................................................................................. 20 The Solanum elaeagnifolium clade ..................................................................... 20 Artificial key to the species of theS. elaeagnifolium clade ............................ 21 Species descriptions .................................................................................... 22 Solanum elaeagnifolium Cav. ...................................................................... 22 Solanum hindsianum Benth. ....................................................................... 47 Solanum homalospermum Chiarini .............................................................. 54 Solanum houstonii Martyn .......................................................................... 57 Solanum mortonii Hunz. ............................................................................ 72 Names not validly published ............................................................................ 75 Acknowledgements ................................................................................................. 75 References .............................................................................................................. 76 Appendix 1. Index to numbered collections ............................................................ 85 Introduction Solanum L. is one of the ten most species-rich genera of flowering plants (Frodin 2004) and has approximately 1,400 species occurring on all temperate and tropical continents. The highest diversity of both groups and species is in tropical South America, concentrated in a circle around the Amazon Basin (see Knapp 2002b), A revision of the Solanum elaeagnifolium clade... 3 but significant diversity occurs in various parts of the Old World. Solanum was one of Linneaus’s (1753) larger genera, with 23 species mostly described from European or African collections. The last time Solanum was monographed in its entirety was in De Candolle’s Prodromus (Dunal 1852), which included 901 spe- cies (with an additional 19 recorded as incompletely known by him at the time). Until the 21st century, the taxonomy of Solanum was largely limited to rearrange- ments of infrageneric taxa, species-level treatments of smaller groups within the genus, and floristic works. The large size of Solanum and its poorly understood infrageneric structure has meant that Solanum taxonomy proceeded in a piecemeal fashion until relatively recently and the genus acquired a reputation of being intractable. A project funded by the United States National Science Foundation’s Planetary Biodiversity Inventory (PBI) program begun in 2004 sought to accelerate species-level taxonomic work across the genus and resulted in a series of monographic and phylogenetic treatments from both Old and New Worlds (e.g., Tepe and Bohs 2011; Stern et al. 2013; Knapp 2013a; Knapp and Voront- sova 2016; Clark et al. 2015; Wahlert et al. 2014, 2015; Aubriot et al. 2016; Vorontsova and Knapp 2016; Spooner et al. 2016). An electronic monographic treatment of the entire genus, with species and species groups added as they are completed, is available online in the web resource Solanaceae Source (http://www.solanaceaesource.org). This treatment is part of that collaborative effort. Taxonomy and relationships Solanum has been divided into 13 major clades (Bohs 2005; Särkinen et al. 2013), of which the spiny solanums (subgenus Leptostemonum Bitter, or the Leptostemonum clade) is the largest, with some 550 currently accepted species. The Solanum elaeagni- folium species group is part of this large group, and within that, is sister to the mono- phyletic Old World clade (see Vorontsova et al. 2013). Plants collected by William Houstoun on the Caribbean coast of Mexico were cul- tivated by Philip Miller of the Chelsea Physic Garden in London and were described as S. carolinense Mill. (= S. houstonii Martyn; Miller 1768). Solanum elaeagnifolium Cav. was described from material grown in the Real Jardín Botánico de Madrid collected on voyages made by Spanish explorers in the early 19th century (Cavanilles 1800); S. lepro- sum Ortega was probably described from the same living material (see Knapp 2013b). Dunal (1813) treated both species as members of his section Leprophora Dunal, along with S. sericeum Ruiz & Pav. (now recognised as a member of the Potato clade, Särki- nen et al. 2015), based on their whitish grey pubescence and leaf morphology. A year later, Dunal (1814) described S. tridynamum Dunal (=S. houstonii) based upon the drawings of José Sessé and Mariano Mociño he had seen either at the herbarium in Geneva or in