Taxonomic Key to the Tomato Species

Leaves, flowers and fruit of several tomato species
Clockwise from top left: S. pennellii, S. chilense, S. peruvianum, S. chmielewskii, S. galapagense, S. pimpinellifolium, S. habrochaites and S. lycopersicum (center). [photo C.M. Rick]

The following species identification key is a revision of the one formulated by Rick et al. (1990) Tomato Genetics Cooperative Report 40: 31. This key has been expanded to include subspecific taxa, as well as four tomato-allied Solanum species. Solanum species names are based on Peralta et al. (2005, 2008).

1. Interior of ripe fruit red; seeds 1.5 mm or longer.
    1.1. Fruit diameter more than 1.5 cm; leaf margins generally serrate.
        1.1.1. Fruit diameter 3 cm or larger, 2-to-many loculed. ...Solanum lycopersicum (formerly Lycopersicon esculentum)
        1.1.2. Fruit diameter 1.5-2.5 cm, 2-loculed. ...S. lycopersicum var. cerasiforme (L. esculentum var. cerasiforme)
    1.2. Fruit diameter less than 1.5 cm, usually ca. 1 cm; leaf margins generally undulate or entire. ...S. pimpinellifolium (L. pimpinellifolium)

2. Interior of fruit yellow or orange; seeds 1.0 mm or shorter ...S. cheesmaniae (L. cheesmanii)
    2.1. Leaves highly subdivided; internodes short, densely pubescent; flowers with large accrescent calyx. ...S. galapagense (L. cheesmanii f. minor)

3. Interior of ripe fruit green or whitish; seeds of varying sizes.
    3.1. Sympodia with 2 leaves.
        3.1.1. Inflorescences with small or no bracts.
   Flowers small (corolla diameter 1.5 cm or less); seeds 1 mm or shorter. ...S. neorickii (L. parviflorum)
   Flowers larger (corolla diameter 2 cm or more); seeds 1.5 mm or longer. ...S. chmielewskii (L. chmielewskii)
        3.1.2. Inflorescences with large bracts.
   Anthers attached in a tube; dehiscent by longitudinal slits.
       Plants erect; peduncle longer than 15 cm; flowers congested; anther tube straight. ...S. chilense (L. chilense)
       Plants spreading; peduncle shorter than 15 cm; flowers more loosely arrayed.
           Inflorescences mostly unbranched; short pubescence; mostly straight anthers. ...S. arcanum (L. peruvianum, L. peruvianum var. humifusum)
           Bifurcate inflorescences; short soft white pubescence; curved anthers; well developed inflorescence bracts.  ...S. peruvianum (L. peruvianum)
            Bifurcate or simple inflorescences; long, glandular pubescence; curved anthers. ...S. corneliomulleri (L. peruvianum, L. peruvianum f. glandulosum)
            Bifurcate inflorescences; very little pubescence; straight or sometimes curved anthers; long peduncle. ... S. huaylasense (L. peruvianum)
     Anthers free, dehiscent through terminal pores; corollas slightly zygomorphic; pedicel articulation usually basal. ...S. pennellii (L. pennellii)
         Leaves and stems puberulous, shiny. ... S. pennellii (L. pennellii var. puberulum)
    3.2. Sympodia with 3 leaves. ...S. habrochaites (L. hirsutum)
        3.2.1. Leaves and stems nearly free of hairs; stems slender, darkly pigmented with anthocyanins. ...S. habrochaites (L. hirsutum f. glabratum)
    3.3. Sympodia with more than 3 leaves.
        3.3.1. Anthers white to cream-colored; leaf margins dissected.
   Leaves and stems pubescent; fruit purplish green, ‹ 1 cm diameter, ripen to hard papery texture. ...S. lycopersicoides
   Leaves and stems glabrous, nearly succulent, lacking anthocyanins; fruit yellowish green, usually ›1 cm diameter, ripen to a hard papery texture. ...S. sitiens (S. rickii)
         3.3.2. Anthers yellow; leaf margins entire, leaflets elliptic to lanceolate
    Leaflets relatively broad, scabrous above, generally 2 pairs of lateral leaflets; fruits 2-3 cm diameter. ....S. juglandifolium
    Leaflets relatively narrow, smooth-velvety above; fruit >2cm diameter. ...S. ochranthum


Peralta, I.E., S. Knapp, D.M. Spooner (2005) New Species of Wild Tomatoes (Solanum Section Lycopersicon: Solanaceae) from Northern Peru. Systematic Bot. 30: 424-434.

Peralta, I.E., D.M. Spooner, and S. Knapp (2008) Taxonomy of wild tomatoes and their relatives (Solanum sect. Lycopersicoides, sect. Juglandifolia, sect. Lycopersicon; Solanaceae).  Systematic Botany Monographs 84.