2n = ploidy missing =48 voucher missing = (Spooner & Hijmans 2001)
Mexico: northeastern Mexico, states of Coahuila, Nuevo León, San Luis Potosí, Tamaulipas, (1230) 1650-3210 m; growing in and at borders of cultivated fields, in pine, oak, juniper, or Opuntia forests, bushy hillsides, grasslands, fencerows.
Solanum hjertingii belongs to the potato clade of Solanum (Bohs, in press). Spooner and Sytsma (1992) placed S. hjertingii in the most derived clade of section Petota based on chloroplast DNA restriction site data. Spooner et al. (2004) erected the Longipedicellata group for S. hjertingii and S. stoloniferum. These two species are polysomic polyploids and 4x(2EBN). There are no clear group-specific morphological characters defining the Longipedicellata group (see discussion in Spooner et al. 2004).
Solanum hjertingii is most similar to S. stoloniferum but is distinguished by its curved styles generally long-exserted (2-8 mm) beyond the tip of the anther tube and glabrous to glabrescent leaves (Spooner et al. 2001). Solanum stoloniferum has straight styles exserted 2-4.5 mm beyond the tip of the anther tube, and strigose, puberulent, or pubescent leaves.
Hawkes (1990) placed six species in ser. Longipedicellata: S. fendleri, S. hjertingii, S. matehualae, S. papita, S. polytrichon, and S. stoloniferum. The specimens Hawkes labeled as these names are all tetraploid (2n = 4x = 48) and grow in the southeastern United States (Hawkes’s S. fendleri) and Mexico. Morphological data (Spooner et al. 2001) supported at best only three species in series Longipedicellata: 1) S. polytrichon, 2) S. hjertingii (including S. matehualae), and 3) S. stoloniferum (including S. fendleri and S. papita). Solanum polytrichon was supported as a species only by a canonical variate analysis, but not by a principal components analysis that intermixed S. polytrichon with many other species, and thus was the least supported species.
Hawkes (1963) designated a specimen at K of Hawkes et al. 1356 as the “type” of S. hjertingii. There are two sheets at K labeled “sheet 1” and “sheet 2,” both labeled as isotypes on labels typed by Hawkes. Sheet 1 has three separate specimens, and Spooner et al. (2004) chose the lowermost as lectotype.
Hjerting and Tarn suggested in the description of S. matehualae (Phytologia 65: 116. 1988) that S. hjertingii was very similar to S. matehualae. Spooner et al. (2001) showed these two species to cluster by morphological data, and Van den Berg et al. (2002) to cluster by RAPD and AFLP data. The only morphological character Spooner et al. (2004) could find to distinguish the two elements is a slight difference in corolla color, with S. matehualae darker purple than S. hjertingii.
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Chloroplast DNA restriction site data available in: Spooner and Sytsma (1992). AFLP, RAPD, and microsatellite data listed in: Van den Berg et al. (2002).