Solanaceae Source

A global taxonomic resource for the nightshade family

Solanum ×michoacanum

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Citation author: 
(Bitter) Rydberg
Citation: 
Bull. Torrey Bot. Club 51: 171. 1924.
Type: 
Based on Solanum jamesii subsp. nayaritense var. michoacanum Bitter, Repert. Spec. Nov. Regni Veg. 12: 9. 1913.
Last edited by: 
Spooner, D.M.
Written by: 
Spooner, D.M.
Habit: 
Herbaceous tuber-bearing perennials 0.3-0.4 m tall. Stems 3-5 mm in diameter at base of plant.
Sympodial structure: 
Sympodial units typically 3-6-foliate.
Leaves: 
Pseudostipules to 8-13 mm long, lunate or lanceolate. Leaves odd-pinnate, 7-11.5 cm long, 4.5-8 cm wide, puberulent adaxially and abaxially; petioles 1-2.7 cm long; lateral leaflet pairs 2-3, the size of the lateral leaflets gradually diminishing gradually towards the base of the leaf; most distal lateral leaflets 3.5-6 cm long, 1-2.5 cm wide, elliptic to elliptic-lanceolate, apex obtuse, acute to acuminate, base oblique, sessile; terminal leaflet 4-7.5 cm long, 1-2 cm wide, lanceolate, apex acute, base attenuate; interjected leaflets absent.
Inflorescences: 
Inflorescence a dichasially branched, ebracteate, monochasial or dichasial cyme, 2-3 forked, generally in the distal half of the plant, with 2-10 flowers, all flowers perfect, peduncle 1-3.2 cm long; pedicels 10-20 mm long, articulate between the proximal ¼ and the distal ¼.
Flowers: 
Flowers with the calyx 5.5-7 mm long, lobes elliptic, apiculate, acumens 1-3 mm long. Corollas 1.5-2.5 cm in diameter, stellate, without acumens, edges of corolla flat, not folded dorsally, white. Anthers 5-6 mm long, connate, yellow, apically poricidally dehiscent and often maturing to a short introrse apical slit, filaments 1-4 mm long. Ovary with style 9-12 mm long, exceeding stamens by 3 mm, straight, with stigma globose.
Fruits: 
Fruits 1 cm in diameter, globose, green throughout.
Seeds: 
Seeds from living specimens often absent, if present 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)

Distribution: 

Mexico (Michoacán), 1900-2100 m; in area of tropical deciduous forest among grasses and shrubs and cacti of old lava fields, growing in areas where S. bulbocastanum and S. pinnatisectum grow.

Phenology: 
Flowering and fruiting July through September.
Phylogeny: 

Solanum ×michoacanum belongs to the potato clade of Solanum (Bohs, in press). Correll (1962) designated S. ×michoacanum as a valid nothospecies originating from a cross of S. bulbocastanum and S. pinnatisectum, based on morphology of artificial hybrids made by Graham and Dionne (1961). Solanum ×michoacanum occurs within the range of both of these species and is morphologically intermediate between them. It is similar to S. trifidum, but differs in its taller stature and globose fruits. Herbarium specimens collected in 1988 (Spooner et al. 1991) suggested the nothospecies is sterile because the fruits were devoid of seeds.

Commentary: 

Spooner et al. (2004) did not locate the holotype of S. ×michoacanum at MPU. Photos of the holotype at G and K make it clear that it was deposited at MPU at one time. Spooner et al. (2004) could choose a lectotype from the holotype photos or abundant isotypes but the holotype may yet surface. The photo of the holotype and isotypes serve well to fix the name.

References: 

Graham, K.M., & L.A. Dionne 1961. Crossability relationships of certain diploid Mexican Solanum species.
Canad. J. Genet. Cytol. 3: 121-127.

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

Spooner, D.M., J. Bamberg, J.P. Hjerting, & J. Gómez 1991. Mexico, 1988 potato germplasm collecting expedition and utility of the Mexican potato species.
Amer. Potato J. 68:29-43.

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.

Genetics: 

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

Taxonomic name: 
Solanum ×michoacanum (Solanaceae)
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