A new species of spiny Solanum (Solanaceae) from Peru

Abstract A new species of Solanum is described from Peru. Solanum junctum S. Stern & M. Nee, sp nov. is a member of the Torva clade of the spiny solanums (Leptostemonum clade). The narrow corolla lobes and recurved prickles of Solanum junctum are similar to species in the Micracantha clade, but Solanum junctum differs in its branched inflorescences and upright green fruits. These characteristics are shared with other members the Torva clade; within this section Solanum junctum is morphologically most similar to Solanum subinerme and Solanum poinsettiifolium. Solanum subinerme has larger flowers, longer cauline prickles, and often has long straight prickles on the adaxial leaf surface that are lacking in Solanum junctum. Solanum poinsettiifolium has fewer spines, dense white tomentum on the abaxial leaf surfaces, stout unbranched inflorescences, and more extensive interpetalar corolla tissue than Solanum junctum.


Introduction
Th e giant genus Solanum L. has been the subject of recent systematic studies due to support from the NSF Planetary Biodiversity Inventory program, including phylogenetic study of the Leptostemonum clade (Bohs 2005;Levin et al. 2006;Weese and Bohs 2007;Stern et al. 2011). Th is clade includes approximately 350-400 species commonly known as the "spiny solanums" due to their epidermal prickles. Species in the group also have long, attenuate anthers and stellate hairs and exhibit a variety of habits, from small herbs to large trees.
Various species in the clade are vines or lianas that climb using recurved prickles. Recurved prickles are uncommon in Solanum and have been used as a synapomorphy to defi ne the Solanum lanceifolium species group (Whalen 1984) also known as sect. Micracantha Dunal (Nee 1999). Stern et al. (2011) conducted a large-scale phylogenetic study of the spiny solanums and found that Solanum species that climb with recurved prickles belong to several diff erent groups, including the Torva, Erythrotrichum, Micracantha, and Old World clades (as defi ned by Stern et al. 2011). Clearly, climbing via recurved prickles is a trait that has evolved multiple times in diff erent lineages.
Revisionary work on the Micracantha clade and phylogenetic study of the large Torva clade has led to the identifi cation of the new species described here. It has been widely collected throughout the central and northern Andes in Peru with specimens dating from the 1920's. Macbride (1962) cited some of these in his treatment of S. heterophyllum Lam. in the Flora of Peru (now recognized as a synonym of S. subinerme Jacq., a species in the Torva clade). He noted that his concept of S. heterophyllum included specimens that were variable and indicated that the specimens cited "may be several species." Indeed, these specimens represent at least three diff erent Solanum species. Nee et al. (2006)  Diagnosis. Similar to S. subinerme Jacq. and S. poinsettiifolium Rusby. Solanum junctum diff ers from S. subinerme in its smaller fl owers, shorter cauline prickles and lack of straight prickles on the adaxial leaf surfaces. Solanum junctum has branched infl orescences and lacks the white tomentum on the adaxial leaf surface and the more abundant interpetalar tissue of S. poinsettiifolium.
Erect or scandent shrub, liana, or small tree, 1-20 m. Stems armed with recurved tan to brown prickles to 5 mm long, the base to 2-4 × 0.5-1 mm, the young stems moderately to densely pubescent with tan to white stellate hairs, the stalks absent to 1 mm, multiseriate, the rays 6-10, ca. 0.5 mm long, the midpoints absent to 0.5 mm, the older stems becoming sparsely pubescent to nearly glabrous. Flowering portions of stem of difoliate sympodial units, the leaves usually geminate, those of a pair often slightly unequal. Leaves simple, the blades 8-12 × 4-7 cm, ovate, chartaceous, green on both surfaces with the adaxial surface typically darker, both surfaces moderately pubescent with hairs like those of the stem, the abaxial surface typically slightly more tomentose and often armed with a few recurved prickles to 2 mm in length on the midrib, abaxial surface with occasional simple glandular hairs below the stellate hairs; venation pinnate, the secondary veins 3-6 on each side of the midvein; base rounded to obtuse, often asymmetrical; margin entire; apex acute to attenuate; petioles 1-3.5 cm, moderately pubescent with hairs like those of the stem, sparsely to moderately armed with prickles like those of the stem. Infl orescence 5-8 (10) cm, extra-axillary, branched with 2-3 (5) main branches, bearing 14-20 fl owers, the plants apparently andromonoecious, with male fl owers lacking a developed style and hermaphroditic fl owers with an elongated style, the axes moderately to densely pubescent with hairs like those of the stem, unarmed; peduncle 2-10 mm; rachis 4-7 (10) cm; pedicels 4-10 mm in fl ower, 8-14 mm in fruit, spaced 1-3 mm apart, articulated at the base. Flowers 5-merous, appearing actinomorphic on herbarium sheets but slightly zygomorphic in the fi eld due to curved anthers, the fl ower buds slightly curved. Calyx 0.5-3 mm long in bud through anthesis, cupular with lobes nearly absent, moderately to densely pubescent with hairs like those of the stem, the calyx splitting into lobes during late fl owering or early fruiting; fruiting calyx lobes 2-3 × 1-2 mm, triangular. Corolla 2-3 cm in diameter, chartaceous, light violet to purple, lobed nearly to the base, the lobes 8-12 × 2-3.5 mm, narrowly triangular, densely pubescent on the abaxial surface with hairs like those of the stem, glabrous to sparsely stellate-pubescent on the midvein on the adaxial surface. Stamens 8-12 mm long; fi laments ca. 0.5 mm long, glabrous; anthers 8-12 × 1-1.5 mm, proximally curving downward with small upward curve at distal end, attenuate, tapering, connivent to weakly spreading, yellow, the base cordate, the apex obtuse, the pores apical, not opening into longitudinal slits with age. Ovary glabrous; style in functionally male fl owers 1-2 × ca. 0.5 mm, style in hermaphroditic fl owers 12-14 × 0.5 mm, exceeding the anthers by 2-3 mm, cylindrical, glabrous; stigma ca. 0.5 mm wide. Fruit a globose berry 1-1.2 cm in diameter, green, glabrous, held upright, with 3-10 fruits per infructescence. Seeds 75-120 per fruit, 3-4 × 2-3 mm, ovate to reniform, brown.
Distribution and phenology. Known from Amazonas, Ayacucho, Junín, Pasco, and San Martín Departments in Peru from 600-1800 m in elevation. Flowering specimens were collected in February-May, July, November-December and fruiting specimens in April, July-August, November. Etymology. Solanum junctum is taken from the Latin "junctus" for "connect or join," referring to the morphological similarities of this species with other sections within the spiny solanums. Th is has been used as an herbarium name on specimen annotations by M. Nee since at least 1995.
Conservation status. Th e conservation status of S. junctum, according to the IUCN Red List Categories (IUCN, 2010) is Least Concern due to the large extent of occurrence (~99,000 km 2 ) and numerous collections (Bachman et al. 2011).
Since Solanum is such a large and diverse group, particularly in the Andes, it is not surprising that many new species and taxonomic diffi culties remain. Th is is particularly true in undercollected areas of the Andes, but recently many inroads have been made (Knapp 2010;Farruggia and Bohs 2010;Tepe et al. 2012;Särkinen et al. 2013). Field collections, revisionary, and phylogenetic study have spurred the description of species that otherwise may remain as "herbarium names".
Both M. Nee and S. Stern recognized S. junctum as a new species from herbarium collections, resulting in the shared authorship of this name. Stern fi rst annotated a specimen as a new species in 2008 (Rodríguez & Leiva 2121 HAO, subsequently destroyed in an herbarium fi re) and Nee has applied the herbarium name S. junctum to specimens since at least 1995 (Schunke 6020 [NY]). Th e type material for S. junctum was selected from the numerous collections made from Prov. Oxapampa in the Department of Pasco, Peru. Ortiz & Mateo 576 was chosen as the type due to the quality of the specimens and wide distribution in herbaria. Th e holotype at NY was the highest quality specimen of those seen and contained abundant fl owering material and developing fruits.
As with many Solanum species with recurved prickles, S. junctum has a variable habit and may be an erect or scandent shrub, vine, or even a small tree. Th e species is unusual in the Torva clade in having fl owers with very narrow corolla lobes with sparse interpetalar tissue, but its branched infl orescences and green upright fruits are shared with many other species in this section. DNA sequence data from specimens of S. junctum have been added to the dataset of Stern et al. (2011) and indicates that S. junctum is a member of the Torva clade but the exact species level relationships remain unclear. Phylogenetic relationships between members of this group are being assessed further using molecular data (S. Stern, in prep.).
Morphologically, the violet to purple fl owers with narrow corolla lobes of S. junctum are similar to those of S. subinerme. Additionally, both species have curved fl ower buds and slightly zygomorphic fl owers due to curved anthers. Th ese species can be diff erentiated by the larger fl owers of S. subinerme, with corollas 3.5-4 cm in diameter (versus 2-3 cm in diameter in S. junctum), the longer cauline prickles in S. subinerme, and presence of long straight prickles on the adaxial leaf surface in S. subinerme, which are lacking in S. junctum. Finally, S. subinerme has thin pedicels that reach 2 cm or more in fruit while those of S. junctum are thicker and only reach 14 mm. Solanum subinerme has a much broader distribution and is found from the Caribbean through northern South America to the Amazon Basin. It is not known from the higher elevations of Peru where S. junctum is found.
Solanum junctum is also similar to S. poinsettiifolium, a species ranging from Dept. Beni, Bolivia along the eastern slope of the Andes to central Peru. Solanum poinsettiifolium is represented by numerous collections from the area where Ucayali, Huánuco, and Loreto Departments intersect. Th ese superfi cially resemble S. junctum as they share similar leaf morphology, fl owers and fruits that are a similar size and color, and both species have curved fl ower buds. Th ese species diff er in that Solanum poinsettiifolium specimens are all described as trees or shrubs, have very few spines on the stem and none on the abaxial leaf surface, and have dense white tomentum with a soft, velvety appearance on the abaxial leaf surfaces. Th e corolla of S. poinsettiifolium has more abundant interpetalar tissue and the infl orescence is stout and unbranched.
Some specimens of S. ovalifolium Dunal (another member of the Torva clade) may also resemble S. junctum. Solanum ovalifolium is a shrub to small tree with much smaller fl owers than S. junctum (corollas typically under 1 cm in diameter in S. ovalifolium vs. 2-3 cm in diameter in S. junctum). Th e infl orescences of S. ovalifolium are generally larger and more branched than those of S. junctum and may branch further up the rachis, whereas the infl orescences in S. junctum branch very near the base. Solanum ovalifolium ranges from Venezuela, Colombia, and Ecuador to Depts. Amazonas and Cajamarca in northern Peru, where its distribution appears to terminate at the Amotape-Huancabamba zone .
It is also possible to confuse S. junctum with S. pedemontanum, a member of the Micracantha clade. At least two specimens of S. pedemontanum (Krukoff 8421 and McDaniel & Rimachi 16879 at NY) have been annotated as possible S. junctum by M. Nee. Macbride (1962) cited specimens belonging to both S. junctum and S. pedemontanum in his taxonomic treatment of S. heterophyllum. While the habit of S. junctum ranges from a vine to shrub, S. pedemontanum is nearly always described as a scrambling vine. In Peru, Solanum pedemontanum tends to occur at lower elevations (100-450 m) than S. junctum (600-1800 m). Th e corolla in S. pedemontanum is white versus the light purple corolla of S. junctum and the corolla lobes of S. pedemontanum are slightly longer (12-20 mm) than those of S. junctum (8-12 mm). Th e infl orescence in S. pedemontanum is unbranched, whereas it branches at the base in S. junctum. Finally, fruits in S. pedemontanum are orange to red whereas they remain green at maturity in S. junctum. Paratypes