2n=24 (Spooner & Hijmans 2001)
Widely distributed throughout Mexico from the northeast (Coahuila, Nuevo León, San Luis Potosí), to central Mexico and south to Oaxaca, (1870) 2100-3500 (4000) m; often in cloud forests, in rich soil in alder, fir, pine, and oak forests, among bushes, roadsides, clearings in woods, among grasses.
Solanum verrucosum belongs to the potato clade of Solanum (Bohs, in press). Spooner and Sytsma (1992) placed S. verrucosum as the sole North and Central American diploid in the terminal clade of section Petota based on chloroplast DNA restriction site data. Hawkes (1990) placed fully half of the members of sect. Petota, including S. verrucosum, into ser. Tuberosa, but ser. Tuberosa is clearly paraphyletic (Miller and Spooner 1999). Solanum verrucosum falls into the highly unresolved cpDNA clade 4 containing members of many series (Spooner and Sytsma 1992; Castillo and Spooner 1997). Solanum verrucosum is the only 2x(2EBN) species in North and Central America and possibly has served as a parent to the polyploids. It frequently is difficult to distinguish from other wild potato species (e.g., S. demissum, S. stoloniferum, S. iopetalum), especially on herbarium specimens where its diagnostic inrolled corolla margins are often not evident because of poorly pressed specimens or lack of flowers (Spooner et al. 1998).
Solanum verrucosum is very similar to some populations of S. stoloniferum and S. demissum. It is best distinguished by the corollas with the edges inrolled dorsally (see plates 3E, 9 of Spooner et al. 2004), but this is difficult to see on poorly prepared specimens.
Hawkes (1990) recognized S. ×vallis-mexici as a triploid nothospecies, formed by hybridization between S. stoloniferum and S. verrucosum. Spooner et al. (2004) had difficulty distinguishing S. ×vallis-mexici from S. stoloniferum using herbarium specimens, and poorly preserved specimens of S. verrucosum could also be confused with either of the above. Spooner et al. (2004) maintained this nothospecies based on some populations documented to be triploid and specimens with a generalized aspect similar to the type (see illustration in Fig. 52 of Spooner et al. (2004).
Schlechtendal first published the name S. verrucosum in Index seminum in horto academico halensi in 1839 collectorum, reprinted in Linnaea 14: 129. 1840 [or 1841]. Spooner et al. (2004) were not been able to locate the original publication. These seed catalogues are extremely rare. The 1839 catalog was not found either by Mabberley (1983; who searched for it at BM, CGE, K, OXF) or Stafleu and Cowan (1985). Spooner et al. (2004) were not been able to locate it from other logical places of deposition at B, C, or HAL. They relied on the description given in the Linnaea reprint but it did not provide the original page of publication.
Schlechtendal described S. verrucosum in detail in 1841. The original publication (as assessed by the Linnaea reprint) bears only a short description and cites no collection number, but Hortus halensis Schlechtendal provides a detailed description and color illustration (reprinted as Plate 9 in Spooner et al. 2004), based on specimens collected by Ehrenberg (no collection number was designated), in Mineral del Monte, on roads, in forests, walls, etc., flowering July to October (no year mentioned). Hawkes (1957) reasoned that the lack of a clear description invalidated the first publication, but this is incorrect because the first publication satisfied the requirements of the Code (see also Mabberley 1983).
Hawkes (1957) showed that specimens of Ehrenberg 80 and Ehrenberg 1132, from Mineral del Monte, from different herbaria, are S. stoloniferum or S. verrucosum, or mixed sheets of both species. He therefore avoided these and chose three “co-lectotypes” for S. verrucosum. One is a specimen from HAL annotated as S. verrucosum by Schlechtendal that now lacks flowers or fruits. This specimen has a typed label of “Mexico: ad vias in muris, per sylvas pr. Mineral Real del Monte frequ. vel cult in Hort. Bot. Hal.” A separate label in Schlechtendal’s handwriting reads “Solanum verrucosum D. F. L. von Schlechtendal, Linn XIX. p. 273.” The second is a sheet at M bearing three specimens, all labeled “Hort bot. Monacensis, 1846”, and the third the illustration in the Hortus halensis of 1841.
Such co-lectotypification is not admissible according to the code, and a single lectotype must be designated. Spooner et al. (2004) rejected the three specimens at M and the illustration because they are dated after the original publication in 1839. The specimen at HAL has the label that suggests it is original material, and Spooner et al. (2004) choose this as lectotype, despite the fact that it lacks flowers or fruits useful for fixing the name. The highly diagnostic illustration in Hortus halensis (1841) demonstrates the author’s intention for this species and is suitable for an epitype. An epitype is a specimen or illustration selected to serve as an interpretive type when the holotype, lectotype, or previously designated neotype, or all original material associated with a validly published name, is demonstrably ambiguous and cannot be critically identified for purposes of the precise application of the name of a taxon (Greuter et al. 2000: 13).
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Spooner, D.M., R.G. van den Berg, & J.B. Bamberg 1995. Examination of species boundaries of Solanum series Demissa and potentially related species in series Acaulia and series Tuberosa (sect. Petota).
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Chloroplast DNA restriction site data available in: Spooner and Sytsma (1992).