Solanum lobbianum

Hawkes (1990) treated Solanum lobbianum as one of the species in Solanum sect. Petota series Tuberosa (Rydb.) Hawkes, but Ochoa (1992) placed the species in series Conicibaccata, a group containing diploids (2n = 24), tetraploids (2n = 48), and hexaploids (2n = 72). The polyploids are mainly distributed from southern Mexico south to central Peru (one species in northern Bolivia), and the diploids from northern Peru to central Bolivia.

The species boundaries and relationships of members of series Conicibaccata have been studied using plastid DNA restriction sites (Castillo and Spooner, 1997), morphology (Castillo and Spooner, 1997; Fajardo et al., 2008), AFLPs (Jiménez et al., 2008), nuclear DNA (“waxy”) sequence data (Spooner et al., 2008), other nuclear DNA sequence data (Fajardo & Spooner 2011), and monographic studies (Hawkes, 1990; Hawkes and Hjerting, 1989; Ochoa, 1990, 1999). The plastid DNA restriction site and morphological data divide the diploids and polyploids into two clades or phenetic groups, respectively, but the morphological separation generally depends on the use of character states that sometimes overlap in range. The DNA sequence data show the polyploids to be of allopolyploid origin from the diploid members of the series and members of species outside of the series.

A monographic study in progress by Fajardo and Spooner, using the above data, and herbarium specimens, will recognize only 17 species. All are very similar, united as a group by conical fruits, leaves with generally parallel-sided morphology, and narrowly ovate to elliptical leaflets. However, some unrelated species also have conical fruits, such as the Mexican diploid species S. hintonii Correll, S. lesteri Hawkes and Hjert. and S. trifidum Correll; the Mexican hexaploid species S. iopetalum (Bitter) Hawkes; and the Bolivian species S. stipulaceum Bitter. An additional problem is that some species possess ovoid fruits that are not absolutely distinct from the conical fruits of the above species or the globose fruits more common in the majority of the members of sect. Petota.

As detailed in Spooner et al. (1995), S. lobbianum illustrates two common problems in sect. Petota about the association of a type specimen with a species: 1) The single type specimen (at the Royal Botanic Gardens, Kew) lacks precise locality data, collection date, or collection number. The only information on the sheet is 'Lobb, Columbia' sic. 2) The specimen lacks fruits.

Three facts complicate the locality of S. lobbianum (Killip, 1932): 1) The place name 'Columbia' is ambiguous because of changing political boundaries and name changes involving Colombia, Ecuador, and Venezuela in the mid-1800's, 2) 'Columbia' possibly was added to the collection by someone other than Lobb, and 3) many of Lobb's 'Col[o]mbian' collections are the only Colombian representatives of species growing elsewhere, and are now implied to be mislabelled (Killip, 1932; Hawkes, 1992).

Bitter (1913) described S. lobbianum. It is small in stature (< 20 cm tall), with pinnately compound leaves, many interjected leaflets, and a blue, rotate corolla. Fruits are lacking. A distinctive feature of the type is its dense pubescence, especially on the under surface of the leaves and in the inflorescence.

Because of the incomplete morphology and vague locality data that hinder the association of the type of S. lobbianum to other collections, other sources have been sought to imply its locality and apply this name to known populations. Unfortunately, sources for Lobb's travels are scant. William Lobb (b. 1809, d. 1864) was a professional collector for the English horticultural firm of James Veitch and Sons, nurserymen specializing in the importation of rare novelties. Information on Lobb's travels written by his employers (H. Veitch, 1881; J. Veitch, 1906) provides scant data. Because of the value of his collections, Lobb likely operated under enforced secrecy regarding his itinerary. All of his letters to his firm unfortunately were destroyed when they went out of business (Killip, 1932). Lobb collected in South America from 1840-1848, with a brief respite home to England in 1844-1845. Secondary sources on Lobb's life and travels (Eastwood, 1911; Dallimore, 1932; Hunkin, 1942; Ewan, 1973; Desmond, 1977; True, 1980) provide no new data relevant to the location of S. lobbianum. Inferences of Lobb's itinerary come from data of presently-known distributions of his other collections, and from extant copies of letters (in the Kew archives) written by J. Veitch and others about Lobb (Hawkes, 1992). These sources show that Lobb's South American travels were wide-ranging, including Brazil, Argentina, Chile, Peru, Ecuador, southern Colombia, and possibly even Venezuela (Killip, 1932).

Hawkes (1992) and Ochoa (1992) provided different hypotheses of the identity of S. lobbianum. Hawkes (1992) identified two wild potato collections with short-conical fruits made in central Ecuador (Chimborazo Province, Spooner, Castillo, and López 5071, 5138, May, 1991) as S. lobbianum, but Spooner et al. (1992) tentatively identified these collections as S. paucijugum Bitter (now synonymized as S. andreanum Baker). Hawkes (1992) attempted to discount a Colombian locality for the type. He cited correspondence in the Kew archives to document Lobb's travels in South America as far north as southern Colombia, and infers he went no farther. He quoted, however, one letter (Kew archives Volume XX, letter 297) “Lobb has left Quito (Ecuador) and gone to Popayán (Colombia) on his way to Venezuela”. Because of the scant evidence for Lobb's travels, Hawkes's (1992) argument that Lobb did not venture farther north than southern Colombia during his entire eight-year stay in South America is unwarranted.

Ochoa (1992), on the other hand, identified two collections with long-conical fruits made in central Colombia (Caldas Department, slopes of Volcán Ruiz, Ochoa 14109, 14110, July, 1980) as S. lobbianum. Spooner et al. (1995) reported collections of wild potatoes with long-conical fruits on the slopes of Volcán Ruiz (Castillo et al. 1211, 1213, 1214) that have overall leaf shape and pubescence very similar to the type of S. lobbianum. These collections have rotate, pale-violet corollas and co-occur with S. colombianum Dunal (Castillo et al. 1212, 1215) with smaller white corollas and long-conical fruits. Hawkes (1990) placed S. lobbianum in series Tuberosa. Later, Hawkes (1992) suggested a relationship with S. multidissectum from Peru.

Solanum lobbianum is characterized by its short stature, densely pubescent leaves and calyx, terminal leaflet slightly larger than lateral leaflets, and secondary interjected leaflets present in terminal leaflet.