Southeastern Brazil in the states of Espirito Santo, Minas Gerais and Rio de Janeiro. Solanum lacteum grows in wet Atlantic forests (Mata Atlântica, Floresta Ombrófila Densa) in forest understory of well preserved sites, from 600 to 1500 m elevation.
Solanum lacteum is a member of the Geminata clade.
Solanum lacteum is characterized by its tiny inflorescences with tightly packed flowers and the difoliate sympodia that are usually not conspicuously geminate. The leaves are narrowly obovate and widest in the distal third. They dry a characteristic blackish brown above and paler brown beneath. The inflorescences often occur internodally and are completely white, including the peduncle and pedicels. The colour of the leaves on herbarium specimens is similar to that of S. caavurana and S. campaniforme, but those species always have leaf pubescence on the lower leaf surfaces and more elongate inflorescences. The highly congested inflorescences of S. lacteum are distinctive and the species is not easily confused with any other growing sympatrically. It is somewhat similar to S. psilophyllum, which is similarly glabrous; differences between these two species are noted in the discussion of S. psilophyllum.
Solanum lacteum grows in the understory of undisturbed forest and can vary from being a tiny subshrub (see Figure 2B in Knapp et al. 2015) to a small treelet ca. 5 m tall. This variation in height is common in members of the Geminata clade and may have to do with plant age and maturity.
Vellozo’s (1831) illustration is not particularly clear, but the congested inflorescences and swollen fruiting pedicels with a slight distal constriction are clearly depicted. In addition, S. lacteum usually has prominent lenticels on the stems; these are also depicted in Vellozo’s plate. The epitype from Rio de Janeiro State supports this suboptimal plate with material that is fertile and shows the key characters (Agra et al. 7298).
We recognise S. cormanthum as a synonym of S. lacteum; after detailed study we consider the plate of S. cormanthum (t. 113) to represent flowering material of the same taxon as that shown in fruit in Vellozo’s plate of S. lacteum (t. 93). Solanum cormanthum was used by both Sendtner (1846) and more recently in the Lista de Especies de Flora do Brasil (Stehmann et al. 2014) to refer to a different taxon we here recognise as a narrow endemic from Minas Gerais (see S. psilophyllum below). Both these authors expressed reservations about the correct application of this name. As is the case with the plate of S. lacteum, the depiction of the plant is not particularly clear, but the small flowers, small anthers and inflorescences that appear axillary (although they are not) are characteristic of S. lacteum. The locality cited for S. cormanthum (“silvis maritimis Regii Praedii S. Crucis”; Vellozo 1829: 86) is well within the geographic range and habitat of S. lacteum, although today it is part of the city of greater Rio de Janeiro.
Sendtner’s (1846) plate of S. glomuliflorum (f. 11-15) clearly shows the scarious-margined calyx with rounded lobes and very plump anthers characteristic of S. lacteum. In his protologue Sendtner (1846) cited two collections of S. glomuliflorum; a flowering specimen of Schott from “Serra d’Estrella” (Serra de Estrela, in Rio de Janeiro State) and a fruiting specimen of Sellow’s from an unspecified locality in Brazil (F neg. 2823; presumably from Berlin]. We selected the Schott specimen at F (accession number 874710; barcode F0073278F) as the lectotype of S. glomuliflorum, as it bears a label with the locality and collector in J.F. MacBride’s handwriting and presumably comes from Berlin where the original is now destroyed. The collection number 5412 noted on this sheet was not mentioned by Sendtner (1846), but he rarely mentioned collection numbers in his citations.
IUCN Standards and Petitions Subcommittee (2014) Guidelines for using the IUCN Red List Categories and Criteria. Version 11. Prepared by the Standards and Petitions Subcommittee. Downloaded from http://www.iucnredlist.org/documents/RedListGuidelines.pdf on 12 Nov 2014.
Knapp S, Giacomin LL, Stehmann JR (2015) New species, additions and a key to the Brazilian species of the Geminata clade of Solanum L. (Solanaceae) in Brazil. PhytoKeys 47: 1-48.
Sendtner O (1846) Solanaceae. In: Martius CFM (Ed.) Flora Brasiliensis 10: 5-200.
Stehmann JR, Mentz LA, Agra MF, Vignoli-Silva M, Giacomin L, Rodrigues IMC (2014) Solanaceae in Lista de Espécies da Flora do Brasil. Jardim Botânico do Rio de Janeiro. Available in: <http://floradobrasil.jbrj.gov.br/jabot/floradobrasil/FB225>. Accessed on: 10 Nov. 2014
Vellozo da Conceicão JM (1829) Flora Fluminensis [“1825”]. Typographia Nacional, Rio de Janeiro.
Vellozo da Conceicão JM (1831) Flora Fluminensis Icones 2 [“1827”]. Senefelder, Paris.
Based on IUCN (2014) guidelines. Near Threatened (NT) B1, 2 a, b(ii, iii); EOO 32,466 km2 (NT); AOO 28 km2 (EN). In spite of its large extent of occurrence, S. lacteum is only known from six locations and we consider it to be at risk due to the fragmentation and loss of its primary forest habitat. Populations in all three states of occurrence, however, are from within protected areas. It is possible that it is more common than it appears, considering that the flowers are so small and inconspicuous that it is easily overlooked.