Endemic to Puerto Rico, known only from the area around Las Tetas de Cayey in the southwestern part of the island in upland forests, from 200 to 800 m.
Solanum ensifolium is a member of the Leptostemonum clade (sensu Weese & Bohs, 2007) and in that group is most closely related to the more widespread S. bahamense; Levin et al. (2006) called these two species the bahamense group. Whalen (1984) had these two taxa as his S. bahamense species group, along with S. polyacanthon.
Solanum ensifolium is most similar and closely related to the widespread S. bahamense. It differs from S. bahamense in its black rather than red berries, shaggy appearance in the new growth and inflorescence due to the presence of stellate trichomes with elongate midpoints and in its higher elevation premontane habitat. In general, S. bahamense grows on calcareous soils near the coast throughout the Caribbean basin, while S. ensifolium is a plant of higher, more inland and slightly wetter elevations on Puerto Rico.
Solanum ensifolium has long been known as S. drymophilum, based on a misinterpretation of the original provenance of the type of S. ensifolium. Michel-Félix Dunal published many new Solanum names based on either drawings from the Sessé and Mociño expedition or material he attributed to “Pavón in herb. Boiss.” (see Knapp, 2008). Many names based on herbarium specimens in G attributed to Pavón are really based on collections from the Sessé and Mociño expedition, and their provenance must be carefully checked against the duplicates of these sheets and manuscripts in MA. Solanum ensifolium is one of these names; the sheet in G-DC used by Dunal to describe this species is a perfect match for a duplicate in MA (MA-604619) labelled “Pto. Rico - Rubias”, the common name for S. ensifolium. This confusion over the provenance of the type of S. ensifolium has meant that the synonym S. drymophilum was in common use for this taxon, until Nee (1999) synonymised it under S. bahamense. It was judged that there were not sufficient reasons to conserve S. drymophilum over S. ensifolium (Committee for Vascular Plants, pers. comm.), so the name S. ensifolium is adopted here and elsewhere (see http://botany.si.edu/Antilles/WestIndies/checklist.htm).
Solanum ensifolium (as S. drymophilum) has been classified as endangered and protected under the U.S. Endangered Species Act (U.S. Fish and Wildlife Service, 1987, 1990, 1992; WCMC, 1998), but recent recognition (Nee, 1999) of this taxon as a synonym of the more widespread S. bahamense has caused confusion as to the conservation status of these populations. When first described in the early 1900s, this species was found across the Sierra de Cayey, a range of foothills in the south eastern region of Puerto Rico (Liogier, 1995), but its range has been severely reduced due to deforestation, land clearing and deliberate eradication (due to a perceived threat to livestock from its prickles), and there is thought to be a single wild population of approximately 200 individuals remaining, in a single two acre site known as the Tetas de Cayey (Miner Solá, 1999).
Many syntypes were cited in the original description of S. drymophilum, the most logical one of these to use as the lectotype is that most widely distributed (Sintenis 2374); no specimens of this taxon used by Schulz were located in B despite intensive searches, we have presumed them destroyed. Lectotypification of S. drymophilum is being undertaken as part of a wider typification study of Caribbean endemic Solanum (Knapp, in press).
Knapp, S. Synopsis and lectotypification of Solanum (Solanaceae) species endemic in the West Indies.
Anales del Jardín Botánico de Madrid, in review.
Whalen, M.D. 1984. Conspectus of species groups in Solanum subgenus Leptostemonum.
Gentes Herbarum 12 (4): 179-282.
U.S. Fish and Wildlife Service 1987. Proposed Listings: Erubia (Solanum drymophilum).
Endangered Species Technical Bulletin 12 (11-12): 6.
U.S. Fish and Wildlife Service 1988. Determination of endangered status for Solanum drymophilum.
Federal Register 53 (166): 32827-32830.
U.S. Fish and Wildlife Service 1992. Recovery plan for Solanum drymophilum.
Prepared by Susan Silander for U.S. Fish and Wildlife Service, Atlanta, Georgia. 17 pp.
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Editorial de la Universidad de Puerto Rico, San Juan, Puerto Rico.
World Conservation Monitoring Centre 1998. Solanum drymophilum.
In: IUCN 2008. 2008 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 14 December 2008.
Nee, M. 1999. Synopsis of Solanum in the New World.
Pp. 285–333 in M. Nee, D. E. Symon, R. N. Lester & J. P. Jessop (eds.), Solanaceae IV: Advances in Biology and Utilization. Royal Botanic Gardens, Kew.
Miner Solá, E. 1999. Arboles y plantas en peligro de extinción en Puerto Rico.
Puerto Rico Ecológico Vol. 3. First Book Publishing of Puerto Rico, San Juan, PR. 91 p.
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Amer. J. Bot. 93: 157-169.
Weese, T.L. & L. Bohs 2007. A Three-Gene Phylogeny of the Genus Solanum (Solanaceae)
Syst. Bot. 32(2): 445-463.
Knapp, S. 2008. Typification of Solanum (Solanaceae) species described by Sessé and Mociño.
Anales del Jardín Botánico de Madrid 65: 7-23.