Origin and taxonomy of potato

Origin

The cultivated potato traces its origin to the region around Lake Titicaca. Domestication occurred from a diploid species within the brevicaule group (in the broad sense; Spooner et al. 2005). More specifically, Solanum candolleanum represents a merger of closely related diploid taxa occurring north of Lake Titicaca, while S. brevicaule now represents a merged group of related species south of the lake.

Archaeological evidence shows that potato tubers were already used around 7000 years ago (Hawkes 1990).Today, most Latin American landraces are tetraploid and short-day adapted (group Andigenum). The diploid cultivated species Solanum phureja is well known for its lack of tuber dormancy (Ghislain et al. 2006).

In southern Chile, long-day-adapted landraces (group Chilotanum) are grown. Early European potato varieties were dominated by Andigenum germplasm, but after the introduction of Chilean potatoes in 1811, Chilotanum germplasm became predominant due to its long-day adaptation (Ames & Spooner 2008; Gutaker et al. 2019). Traits such as long-day adaptation, shallow eyes and oblong tubers are typical for Chilotanum and rare in Andigenum (Ghislain et al. 2009).

Taxonomy

Potato belongs to the family Solanaceae, genus Solanum, subgenus Potatoe, section Petota. Classic taxonomists (Ochoa, Hawkes, Bukasov) disagreed on various points (Spooner & van den Berg 1992), leading to long-standing inconsistencies.For detailed reviews, see Spooner & Hijmans (2001) and van den Berg & Groendijk-Wilders (2014).

Traditional classification

The historically most used framework is Hawkes (1990), recognising 232 species in 19 series.Examples of former taxonomic confusion include:

• S. bukasovii vs. S. multidissectum
• S. brachycarpum vs. S. iopetalumAs a result, genebanks may use different species names for the same accession.

Modern revisions

Spooner and colleagues revised potato taxonomy using morphological and molecular data. A selection of key changes:

• S. palustre and S. brevidens merged under S. palustre (Contreras & Spooner 1999)
• S. toralapanum → subspecies of S. megistacrolobum (Giannattasio & Spooner 1994a,b)
• S. microdontum subsp. microdontum and subsp. gigantophyllum merged (van den Berg & Spooner 1992)
• S. astleyi → subspecies of S. boliviense (Spooner et al. 1997)
• S. canasense merged with S. bukasovii (Ochoa 1992), later included in S. candolleanum alongside 40 additional taxa (Spooner & Salas 2006; Spooner et al. 2014)
• S. fendleri, S. leptosepalum, S. papita, S. polytrichon → merged into S. stoloniferum (Spooner et al. 2004)
• S. tarijense merged with S. berthaultii (Spooner et al. 2007)
• 32 taxa placed in a polymorphic brevicaule group and synonymised (Spooner et al. 2014)

Cultivated species revisions

Ghislain et al. (2006) demonstrated that S. phureja was taxonomically unstable: 31% of accessions at CIP were tetraploid rather than diploid, challenging the classic definition.Spooner et al. (2007) further showed that many S. phureja accessions cluster with tetraploids, leading to the merger of S. phureja and S. stenotomum with S. tuberosum subsp. andigena.

CGN’s own evaluation found all its phureja accessions to be diploid.

Some changes remain debated—for instance, merging S. megistacrolobum with S. boliviense (Jacobs et al. 2011). SNP data from Hardigan et al. (2015) show PI 265873 (former S. megistacrolobum) does not cluster with S. boliviense accessions, suggesting misclassification.

Current accepted taxonomy

The most up-to-date treatment is provided by:

• Spooner et al. (2014) – reducing wild species from 225 → 107 and cultivated species from 7 → 4.
• GRIN Taxonomy – lists current species and synonyms for Solanum.

Spooner et al. (2018) offer a reduced phylogenetic structure based on 131 diploid accessions.

Images and application in genebanks

Pictures are available at CGN at the accession level and a representative one is selected for the species level. CGN has not fully adopted all recent synonymisations (e.g. brevicaule and candolleanum groups), as genebanks traditionally apply nomenclatural changes conservatively to maintain stability.

Potato Taxonomists

Selected popular-science articles by Michael Jackson on potato taxonomy:

• How long is a piece of string? (2018-01-09)
• The humble spud (2015-02-26)
• Potatoes – the real treasure of the Incas (2012-02-18)

A list of potato taxonomic monographs is available.