Solanaceae Source

A global taxonomic resource for the nightshade family

Solanum tarnii

Citation author: 
J. G. Hawkes & Hjerting
Phytologia 65: 114. 1988.
Mexico. Hidalgo: Hwy 85 from Zimapán to Tamazunchale at Las Trancas, about 6 km E along track towards Nicolás Flores, 2420 m, 6 Sep 1983, T. R. Tarn, R. W. Ross, & J. Gómez 62 (holotype: K, cultivated from seeds collected in Mexico in 1983 and grown and harvested in a field at Sturgeon Bay, Wisconsin in 1988; the holotype and isotype are clearly labeled as such by the author!; isotypes: BM!, C!, K!). Note: Spooner et al. (2004) saw 15 more isotypes at K that are being distributed by K to herbaria worldwide.
Last edited by: 
Spooner, D.M.
Written by: 
Spooner, D.M.
Herbaceous tuber-bearing perennials 0.6-1 m tall. Stems 2.5-5 mm in diameter at base of plant.
Sympodial structure: 
Sympodial units typically 3-6-foliate.
Pseudostipules to 2-5 mm long, lunate. Leaves odd-pinnate, 8-15 cm long, 6-10 cm wide, pilose adaxially and abaxially; petioles 1-1.5 cm long; lateral leaflet pairs 3-5, the size of the lateral leaflets diminishing abruptly towards the base of the leaf; most distal lateral leaflets 3-5 cm long, 0.6-1.5 cm wide, lanceolate to elliptic-lanceolate, apex acute to apiculate, base cordate, rounded, cuneate to oblique, sessile to petiolate, with petiolules up to 3-8 mm; terminal leaflet 3-5 cm long, 0.6-1.5 cm wide, lanceolate to elliptic-lanceolate, apex acute to acuminate, base cuneate; interjected leaflets 4-10.
Inflorescence a dichasially branched, ebracteate, monochasial or dichasial cyme, 2-3 forked, generally in the distal half of the plant, with 5-15 flowers, all flowers perfect, peduncle 3-13 cm long; pedicels 12-35 mm long, articulate between the proximal ¼ and the distal ¼.
Flowers with the calyx 10-13 mm long, irregularly lobed, lobes oblong to lanceolate, apiculate to caudate, acumens 2-6 mm long. Corollas 1.4-3 cm in diameter, stellate, without acumens, edges of corolla flat, not folded dorsally, white. Anthers 5-9 mm long, connate, yellow, apically poricidally dehiscent and often maturing to a short introrse apical slit, filaments 1-4 mm long. Ovary with style 8-13 mm long, exceeding stamens by 2-3 mm, straight, with stigma globose.
Fruits 1.5-2 cm in diameter, globose to ovoid, green with dark green stripes and white spots.
Seeds from living specimens green-white throughout, ovoid, ca. 2 mm long, with a thick covering of “hair-like” lateral walls of the testal cells that make the seeds mucilaginous when wet. Removal of these hair-like lateral walls by enzyme digestion reveals a honeycomb pattern at their base.
Chromosome number: 

2n = ploidy missing =24 voucher missing = (Spooner & Hijmans 2001)


Mexico: only widely scattered collections are known from Hidalgo, Querétaro and Veracruz, 2000-2600 m; in and at margins of cultivated fields, pine and oak forests, among maguey, among scrub vegetation and rocks, roadsides.

Flowering and fruiting September through October.

Solanum tarnii belongs to the potato clade of Solanum (Bohs, in press). Spooner and Sytsma (1992) placed S. tarnii and all other North and Central American diploids (exclusive of S. bulbocastanum, S. cardiophyllum, and S. verrucosum) in the basal “clade 1” of section Petota based on chloroplast DNA restriction site data. Spooner et al. (2004) placed S. tarnii and S. trifidum in the Trifida group. Correll (1952) erected Solanum ser. Trifida to accommodate the sole species S. trifidum, and Correll (1962) and Flores Crespo (1966) followed him. Bukasov (1978) included this species and S. ×michoacanum in ser. Tridifa, but Hawkes (1990) included ser. Trifida in ser. Pinnatisecta. Solanum tarnii and S. trifidum are united by chloroplast DNA data (Spooner and Sytsma 1992), morphological data (Lara Cabrera and Spooner, in press a ), and AFLP data (Lara Cabrera and Spooner, in press b). There is no single character morphological uniting the two species, however. They are easily distinguished from each other in the field, especially by the globose fruits of S. tarnii vs. the conical fruits of S. trifidum.


Solanum tarnii is similar to many other white-flowered diploid species from North and Central America but is distinguished by its relatively long calyx (10-13 mm long) with long acumens (2-6 mm long).


Lara-Cabrera, S. & D.M. Spooner Taxonomy of Mexican diploid wild potato (Solanum sect. Petota) species: AFLP data.
Plant Syst. Evol.

Lara-Cabrera, S. & D.M. Spooner Taxonomy of Mexican diploid wild potato (Solanum sect. Petota) species: morphological and microsatellite data.
Monogr. Syst. Bot., Missouri Bot. Gard.

Correll, D.S. 1952. Section Tuberarium of the genus Solanum of North America and Central America.
U.S.D.A. Agric. Monogr. 11: 1-243.

Correll, D.S. 1962. The potato and its wild relatives.
Contr. Texas Res. Found., Bot. Stud. 4: 1-606.

Flores Crespo, R. 1966. Estudio preliminar del genero Solanum, seccion Tuberarium subseccion Hyperbasarthrum en México.
Thesis, México, D. F.: Univ. Nac. Autonoma de México.

Bukasov, S.M. 1978. Systematics of the potato (In Russian).
English translation of article first appearing in Trudy Prikl. Bot. 62: 3-35. In Systematics, Breeding, and Seed Production of Potatoes, ed. V. S. Kothetar, translator, A. K. Dhote, 1-42. New Delhi: Amerind Publ. Co.

Hawkes, J.G. 1990. The potato: evolution, biodiversity and genetic resources.
Oxford: Belhaven Press.

Spooner, D.M. & K.J. Sytsma 1992. Reexamination of series relationships of Mexican and Central American wild potatoes (Solanum sect. Petota): evidence from chloroplast DNA restriction site variation.
Syst. Bot. 17:432-448.

Spooner, D.M. & R.J. Hijmans 2001. Potato systematics and germplasm collecting, 1989-2000.
Amer. J. Potato Res. 78:237-268; 395.

Lara-Cabrera, S.I. 2001. Taxonomy of Mexican diploid wild potato (Solanum sect. Petota) species: a morphological and molecular study.
Ph.D. Thesis, Plant Breeding and Plant Genetics Program, University of Wisconsin-Madison.

Spooner, D.M., R.G. van den Berg, A. Rodríguez, J. Bamberg, R.J. Hijmans, & S.I. Lara-Cabrera 2004. Wild potatoes (Solanum section Petota; Solanaceae) of North and Central America.
Syst. Bot. Monog. 68: 1-209 + 9 plates.

Bohs, L. 2005. Major clades in Solanum based on ndhF sequences.
Pp. 27-49 in R. C. Keating, V. C. Hollowell, & T. B. Croat (eds.), A festschrift for William G. D’Arcy: the legacy of a taxonomist. Monographs in Systematic Botany from the Missouri Botanical Garden, Vol. 104. Missouri Botanical Garden Press, St. Louis.


Chloroplast DNA restriction site data available in: Spooner and Sytsma (1992). AFLP, morphological, and microsatellite data listed in: Lara-Cabrera (2001).

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