Solanum stoloniferum

Solanum stoloniferum is one of the most common, widespread, and polymorphic species of wild potatoes from North and Central America. It is very similar to some populations of S. demissum, S. hjertingii, and S. verrucosum. Solanum stoloniferum has pedicel articulation below the distal ¼ of the pedicel, flat corolla margins, and straight styles exserted only 0.4.5 mm beyond the tip of the anthers (Spooner et al. 2001). Solanum demissum has pedicel articulation in the upper ¼ of the pedicel, S. hjertingii has curved styles exserted 2-8 mm beyond the tip of the anthers, and S. verrucosum has corollas with the edges inrolled dorsally.

Van den Berg et al. (2002) showed S. polytrichon to be completely intermixed with S. stoloniferum (including S. fendleri and S. papita) in an analysis of AFLP data. A reexamination by Spooner et al. (2004) of living accessions previously identified as S. polytrichon at Sturgeon Bay Wisconsin in 2001 showed putative diagnostic characters of spreading pubescence, enlarged terminal leaflets, and white corollas to vary tremendously in this species. For example, Graham 250, 256, 315, 358; Hawkes 1468; Ochoa 14178, possessed a clear expression of dense spreading pubescence, enlarged terminal leaflets, and white corollas. Other accessions, however, are impossible to clearly and consistently distinguish as S. polytrichon and were supported as species in the canonical variate analysis only by widely overlapping character states. For example, Tarn et al. 235, Rodríguez 2558, 2571; Spooner et al. 4109, have only few spreading hairs, and Tarn et al. 212 and Spooner et al. 4118 have purple corollas. Accessions identified as S. papita (Correll 20075 and Tarn et al. 114) have white corollas and spreading hairs. There is such an intergradation of these “species-specific” character as to make S. polytrichon untenable to recognize.

There is a tendency for S. stoloniferum to be of shorter stature with fewer interjected leaves in the northern than in the southern part of its range, and these northern populations have been named S. fendleri. There are so many exceptions to these characters however (e.g., Blumer 1566, type of S. fendleri subsp. arizonicum, that is taller; or Blumer 1579 or Lemmon 2845 from Arizona with up to four sets of interjected leaflets) that height alone fails to distinguish these formerly recognized species.

Solanum stoloniferum can easily be confused with some landraces of S. tuberosum. Solanum tuberosum often has wider leaflets and longer peduncles than S. stoloniferum, and some landraces have pink corollas (never pink in S. stoloniferum). Solanum tuberosum is so variable, however, (including cultivars with narrower leaflets, shorter peduncles, and white or blue or purple corollas; e.g., Mexia 2658 at E, RSA) that the two taxa may be impossible to distinguish consistently and reliably on herbarium sheets.

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 herbarium specimens of S. ×vallis-mexici from S. stoloniferum, and poorly preserved specimens of S. verrucosum could also be confused with either of them. Spooner et al. (2004) maintained this nothospecies based on some populations documented to be triploid and specimens with a generalized aspect of S. ×vallis-mexici.

Spooner et al. (2004) illustrated some of this variability in their Figs. 32 (the type of S. fendleri, illustrating a short plant with few lateral leaflets and an enlarged terminal leaf), Fig. 33 (the type of S. polytrichon, illustrating a densely pubescent plant with few lateral leaflets and enlarged terminal leaflet), and Fig. 34 (a common morphotype of S. stoloniferum, a taller plant with more, and subequal-sized lateral and terminal leaflets). Correll (1962) also was confounded by tremendous variation in S. stoloniferum, but recognized names Spooner et al. (2004) placed under S. stoloniferum and suggested even the need to segregate species from S. stoloniferum. This broad synonymy in S. stoloniferum runs counter to the supposition of Correll (1962: 374):

“It is quite probable that when lengthy detailed field studies are made a different, more strict, interpretation of this species will result in the segregation of several rather well defined entities.”

Schlechtendal first published S. stoloniferum in Linnaea 8: 255 [May or June] 1833, and he and Bouché reported on this species in detail a few months later in Verh. Ver. Preuss. Gartenb. 9: 319, tab. 2 [September] 1833. Hawkes (1957) reasoned that the lack of a clear description and confusion in location of the type invalidated the first publication, but this is incorrect because the first publication satisfied the requirements of the Code. Hawkes (1957) chose a lectotype of S. stoloniferum, a cultivated specimen from the Berlin Botanic Gardens, grown from tubers collected in the wild, now deposited at UPS. Hawkes’s lectotypification must be followed, but his opinion that the name was not validly published in Linnaea is rejected.

Hawkes (1944) designated Balls et al. 4864 as the type of S. malinchense, and Balls et al. 5097 as the type of S. longipedicellatum var. longimucronatum, but more than one specimen of these numbers exist, necessitating that Spooner et al. (2004) choose a lectotype. Also, K has two sheets each labeled with the same numbers as these type collections, but thesr specimens are taken from plants cultivated later and thus are not type material.

Bitter (1912) based S. schizostigma on A. Aschenborn 306, from an unknown locality in Mexico. The holotype was destroyed and no duplicates have been located. The proximal part of the plant is unknown. The pseudostipules and medial pedicel articulation clearly identify it as a member of sect. Petota. Despite an excellent description, Correll (1952, 1962) and Hawkes (1990) could not assign this name to any accepted species, although Hawkes suggested it may apply to S. cardiophyllum or S. hintonii. The anthers 5-5 1/2 mm long preclude S. cardiophyllum, and the subrotate corollas preclude any 2x(1EBN) diploid species. The white subrotate corollas, styles 8-9 mm long and ovoid fruits identify S. schizostigma as S. stoloniferum.

Spooner et al. (2004) were not able to locate the types of S. orbiculatibaccatum or S. coriaceifoliolatum despite searches at WIR. Correll (1952, 1962) and Hawkes (1990) both ally both of them with the “collective species” S. stoloniferum. The description of S. orbiculatibaccatum falls entirely within the range of morphology of S. stoloniferum. The description of S. coriaceifoliolatum is ambiguous and Spooner et al. (2004) placed it in doubtful and excluded names.