Citation:
Syst. Bot. 30: 429. 2005.
Type:
Peru, Amazonas: western base of the Cerros Calla Calla, 9 km E of Balsas on road to Leimebamba, 1340 m, 30 May 1964, Hutchison et al. 5449 (holotype, USM; isotypes: F, K, M, MICH n.v., MO, NY, UC, US).
Written by:
Peralta, I.E., S. Knapp & D.M. Spooner
Habit:
Spreading, erect or often prostrate, perennial herbs, woody at the base, to 1 m tall, to 1 m or more in diameter. Stem 7-12 mm in diameter at base, green, glabrous to variously pubescent with a mixture of simple uniseriate trichomes, short trichomes to 0.5 mm long, (these eglandular or with a 1-celled head), longer patent trichomes to ca. 1 mm long, from multicellular bases, short glandular trichomes with 1-celled or multicellular heads, some populations (Chota Valley ) with very sparse short unicellular trichomes.
Sympodial structure:
Sympodial units 2-foliate; internodes 2-6 cm long.
Leaves:
Leaves interrupted imparipinnate, (3-) 5-15 (--25) cm long, (1) 2.5-7 (-10) cm wide, green to pale beneath, glabrous to sparsely short pubescent to densely pubescent with a mixture of simple uniseriate trichomes, some populations lacking stout patent trichomes to 1 mm long on the leaves, adaxially nearly glabrous with a few scattered 1-celled trichomes to densely pubescent with short and long trichomes, abaxially the pubescence more abundant, with more stout trichomes to 1 mm long, along the veins; primary leaflets 2-4 (--5) pairs, the basal pair half the size of the rest, elliptic to broadly elliptic, the base acute to truncate, oblique and decurrent basiscopically, the margins almost entire (Jequetepeque) to regularly or irregularly crenate-serrate to lobed, the apex acute; terminal leaflet usually longer than the lateral leaflets, 1.2-5 cm long, 0.6-2 (-2.5) cm wide, the petiolule 0.5-1 cm long, the apex long-acuminate in Marañón populations; lateral leaflets 0.7-3.5 (-5) cm long, 0.4-2 (2.5) cm wide, the petiolule 0.2-1 cm long; secondary leaflets occasionally present acroscopically on the larger leaflets, 0.1-0.2 cm long, 0.1-0.2 cm wide, sessile; tertiary leaflets absent; interjected leaflets 0-8, 0.1-0.5 cm long, 0.1-0.4 cm wide, decurrent on the leaflet rachis; petiole 0.5-2.5 (-3.5) cm long; pseudostipules present but not developed at all nodes, 0.5-1 cm long, 0.5-1 cm wide, the margin entire to irregularly crenate.
Inflorescences:
Inflorescences 6-20 cm long, simple, with 5-20 flowers, ebracteate or nearly all the nodes bracteate, the bracts 0.1-0.4 (-1) cm long, 0.1-0.2 (-1) cm wide, larger in the basal nodes, peduncle (1.5-) 3.5-10 cm long, glabrous and minutely glandular to densely velvety pubescent with intermixed longer patent trichomes like those of the stems. Pedicels 1.1-1.7 cm long, articulated at the middle or in the distal half. Buds 0.8-1 cm long, 0.3-0.4 cm wide, conical, straight, with the corolla approximately half way exserted from the calyx just before anthesis.
Flowers:
Flowers with the calyx tube minute, the lobes 0.5-0.7 cm long, 0.15-0.2 cm wide, lanceolate, glabrous to pubescent like those of the inflorescence; corolla 1.8-2 cm in diameter, pentagonal, yellow, the tube 0.5-0.6 (-0.8) cm long, the lobes 0.8-1 cm long, 0.8-1 cm wide, white pubescent on the tips and margins, reflexed at anthesis; staminal column 0.8-0.9 cm long, straight, the filaments 0.25-0.5 mm long, the anthers 0.4-0.5 cm long, the sterile apical appendage 0.1-0.25 cm long; ovary globose, glabrous or with a few minute trichomes at the apex; style 0.8-1 cm long, ca. 0.5 mm in diameter, densely white pubescent in the basal half, straight, scarcely exserted to exserted ca. 0.5 mm from the staminal column; stigma capitate, green.
Fruits:
Fruit 1-1.4 cm in diameter, globose, 2-locular, green with a dark green stripe from the apex to the base, that could change to purple at maturity, glabrous to more or less densely pubescent with weak-walled simple uniseriate trichomes less than 0.5 mm long; fruiting pedicels 1.5-2.3 cm long, angled towards the inflorescence axis, occasionally straight; calyx lobes in fruit 0.9-1 cm long, 0.2-0.25 cm wide, spreading to loosely investing the berry.
Seeds:
Seeds 2.2-3.2 mm long, 1.2-1.6 mm wide, 0.5-0.6 mm thick, obovate, pale brown pubescent with hair-like outgrowths of the lateral testa cell walls, which give a silky appearance to the surface, narrowly winged at the apex and acute at the base.
Distribution:
Coastal and inland Andean valleys in northern Peru; in lomas, dry valleys and dry rocky slopes; 100 to 2500 m.
Phenology:
Solanum arcanum flowers and fruits sporadically throughout the year; populations in the lomas formations appear to flower in the foggy season (September to November), but this varies with rainfall and El Niño events.
Phylogeny:
Solanum arcanum is a member of the Potato clade (sensu Weese & Bohs, 2007); within the tomatoes and wild relatives it is a member of the “Arcanum group” and is a member of section Lycopersicon.
References:
Rick, C.M., E. Kesicki, J.F. Fobes, & M. Holle 1976. Genetic and biosystematic studies on two new sibling species of Lycopersicon from Interandean Perú.
Theor. Appl. Genet. 47: 55-68.
Rick, C.M. 1986. Reproductive isolation in the Lycopersicon peruvianum complex.
In Solanaceae, biology and systematics, ed. W. G. D’Arcy, 477–495. New York, New York: Columbia University Press.
Bai, Y., R. van der Hulst, C.C. Huang, L. Wei, P. Stam, & P. Lindhout 2004. Mapping OI-4, a gene conferring resistance to Oidium neolycopersici and originating from Lycopersicon peruvianum LA2172, requires multi-allelic, single-locus markers.
Theor. Appl. Genet. 109: 1215-1223.
Peralta, I.E., S. Knapp & D.M. Spooner 2005. New Species of Wild Tomatoes (Solanum Section Lycopersicon: Solanaceae) from Northern Peru.
Syst. Bot. 30(2): 424-434.
Taxonomic name:
Solanum arcanum is a member of a clade containing S. neorickii and S. chmielewskii, and is sister to them. It can be distinguished from them by its generally more finely crenate leaflets (leaflets of the other two species usually have more widely spaced crenations), larger inflorescences with more flowers and the more complex mix of trichome types. Solanum arcanum and S. neorickii are sympatric in northern Peru with, but they can easily be distinguished as S. arcanum has much larger corollas (1.8-2 cm in diameter vs. 1-1.2 cm in diameter) and more flowers per inflorescence (10 vs. 7). Accessions we now recognize as S. arcanum did not cross successfully with either S. chmielewskii or S. neorickii (Rick et al. 1976), leading Rick to believe that they were not closely related. We do not feel crossability is a reliable indicator of relationship in the tomatoes and their relatives.
Solanum arcanum is an extremely variable species, comprising of four weakly defined morphotypes (“assemblages”) with discrete geographic ranges. The complex overlapping variability, especially in leaf morphology, dissuades us from recognizing these as formal taxa. The table lists all the TGRC accessions (LA numbers) previously included in Rick’s broad definition of S. peruvianum with their current identification; the assemblages of S. arcanum to which individual accessions belong are also indicated.
A. ‘Marañón’ Assemblage. Robust erect plants, sometimes to 1 m tall, decumbent when mature; little to no velvety pubescence, with dense long patent trichomes, leaflets dentate or more deeply incised; growing in the Río Marañón Valley (includes the type of Solanum arcanum, Hutchison et al. 5449). This includes the Chamaya-Cuvita and the Marañón assemblage of races that Rick (1986 a) recognized as closely related based on their interfertility in experimental crosses.
B. ‘Humifusum’ Assemblage. Slender prostrate plants; pubescence velvety; leaflets entire or with only a few marginal teeth, velvety pubescent on the abaxial side, and dark green; inflorescence unbranched; growing in Pacific drainages. The type of Lycopersicon peruvianum var. humifusum (Blood & Tremelling 42) comes from among these populations.
C. ‘Chotano’ Assemblage. Slender prostrate plants; almost completely glabrous; lateral leaflets deeply lobed; growing in the Río Chota Valley near Yamaluc in the Department of Cajamarca (e.g., Sanchez Vega 2291). The ‘humifusum’ and ‘Chotano’ assemblages appear to be closely related based both on interfertility(Rick 1986a), and molecular sequence data (Peralta & Spooner 2001), and differ mainly in pubescence.
D. ‘Lomas’ Assemblage. Slender prostrate to semi-erect plants; pubescence velvety; leaflets dentate or almost entire; inflorescences simple or sometimes branched; growing at the Lomas of Cerro Campana and Virú (e.g., Dillon et al. 2703). These populations are incredibly variable from year to year; specimens collected in El Niño years have very large leaves, while those collected in drier seasons have smaller, more pubescent leaves with fewer leaflets and less lobed margins. The ‘Lomas’ populations are quite variable in morphological characters, such as inflorescence branching pattern, and appear morphologically somewhat like southern populations of S. peruvianum s.s.
Genes for resistance to powdery mildew have been identified in S. arcanum (LA2172, Bai et al. 2004). A list of TGRC accessions previously identified as L. peruvianum s.l. but now recognized as S. arcanum can be found in Peralta et al. (2005).
Because these northern populations could be crossed successfully with S. chilense but not with S. peruvianum s.s., Rick (1986a) suggested that they were ancestral to the rest of the “peruvianum complex,” and that northern Peru was a major site of evolutionary development in the wild tomatoes. .
Specimens of S. arcanum grown in cultivation tend be vigorous plants, with larger stems, internodes, leaves, inflorescences, flowers, and fruits than specimens collected from the wild, but they maintain similar characters found in wild specimens collected in similar geographic areas, and the cultivated accessions generally can also be assigned to the four assemblages mentioned above.