2n = 2x = 24 voucher: Okada 5074 (BAL) (Hijmans, et al. 2007)
Solanum malmeanum occurs widely in Argentina (Provs. Buenos Aires, Corrientes, Chaco, Entre Ríos, Formosa, Misiones, Santa Fé), Brazil (Río Grande do Sul), Paraguay (Boquerón, Central, Presidente Hayes, Itapará, Cordillera), Uruguay (Colonia, Maldonado). In palm forests, in or at the edges of woods, in cleared woods or inundated savannas, or as a weed in cultivated fields of maize, manioc, sweet potato, cotton, potato, sorghum, or Citrus plantations, in disturbed soil, coasts of rivers, 0-330 m in elevation.
Solanum malmeanum is a member of Solanum sect. Petota Dumort., the tuber-bearing cultivated and wild potatoes. Within sect. Petota, Solanum malmeanum is a member of a very diverse clade related to the cultivated potato. On a higher taxonomic level, it is a member of the informally-named Potato Clade, a group of perhaps 200-300 species that also includes the tomato and its wild relatives (Bohs, 2005).
Solanum malmeanum is sympatric with S. commersonii and S. chacoense. It can be differentiated from S. commersonii by its generally subequal uppermost lateral leaflets that do not decrease rapidly in size towards the base, by its generally petiolulate and larger lateral leaflets, and by its white flowers. The flowers are almost always white, although in a very few cases we have observed a small bluish spot very different from the characteristic dark stripes along the rays abaxially in flowers of S. commersonii. These populations could represent probable hybrids between S. malmeanum and S. commersonii. From S. chacoense it can be differentiated by its smaller and sometimes rosette-forming habit, by the obtuse to more rarely acute apex of the terminal leaflet, and generally by a shorter peduncle.
Hawkes and Hjerting (1969) and Hawkes (1990) considered S. malmeanum and S. commersonii as subspecies of S. commersonii and distinguished subsp. malmeanum from subsp. commersonii by the bases of leaflets decreasing gradually towards the base of the leaf, narrowly decurrent to petiolulate leaflets, low to median pedicel articulation, and corolla always white. Correll (1962) treated subspecies malmeanum as a form of S. commersonii and distinguished it from S. commersonii by the presence of at least some petiolulate leaflets and often two or more interjected leaflets. Mentz and Oliveira (2004) stated that some populations of S. malmeanum, when grown in glasshouses, did not maintain the white color of their flowers and consider these populations as possible hybrids. We have not seen this behavior in the populations we grew. Mentz and Oliveira (2004) considered S. malmeanum as a form of S. commersonii, but questioned the validity of even this rank on the basis of the differences stated.
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