''Digitalis'' sect. ''Isoplexis'' is a

section Section, Sectioning, or Sectioned may refer to: Arts, entertainment and media * Section (music), a complete, but not independent, musical idea * Section (typography), a subdivision, especially of a chapter, in books and documents ** Section sig ...

of four

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

s within the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

Digitalis ''Digitalis'' ( or ) is a genus of about 20 species of herbaceous perennial plants, shrubs, and Biennial plant, biennials, commonly called foxgloves. ''Digitalis'' is native to Europe, Western Asia, and northwestern Africa. The flowers are ...

'' in the plantain family

Plantaginaceae Plantaginaceae, the plantain family or veronica family, is a large, diverse family (biology), family of flowering plants in the order Lamiales that includes common flowers such as Antirrhinum, snapdragon and Digitalis, foxglove. It is unrelated ...

. The species of section ''Isoplexis'' differ from other plants in the genus ''

'' in that their monosymmetric (sometimes called

zygomorphic Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts. Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spir ...

) flowers have a distinctive large upper lip rather than large lower lip and the species are endemic to the

Canary Islands The Canary Islands (; ) or Canaries are an archipelago in the Atlantic Ocean and the southernmost Autonomous communities of Spain, Autonomous Community of Spain. They are located in the northwest of Africa, with the closest point to the cont ...

(the species ''D. canariensis'', ''D. chalcantha'', and ''D. isabelliana'') and

Madeira Madeira ( ; ), officially the Autonomous Region of Madeira (), is an autonomous Regions of Portugal, autonomous region of Portugal. It is an archipelago situated in the North Atlantic Ocean, in the region of Macaronesia, just under north of ...

(''D. sceptrum'').

Taxonomy

Two ''Isoplexis'' species, ''D. canariensis'' and ''D. sceptrum'', were first described by

Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

in 1753 as part of the genus ''Digitalis''. Since then the section has undergone several changes, the addition of two more species and more importantly being moved to a separate genus, under the genus name of ''Isoplexis'' or sometimes ''Callianassa'', back and forth many times (Lindley 1821, Loudon 1829, Bentham 1835, Webb 1845, Wetstein 1891, Himmelbaeur and Zwillinger 1927, Werner 1960–1966, Heywood 1972). The position of ''Isoplexis'' as a section within ''Digitalis'' was finally proven by Carvalho in 1999 using molecular data and published by Brauchler et al. in 2004.

Ecology

Habitat

''Isoplexis'' species grow in woody habitats: ''D. canariensis'' in humid woodland areas and rarely in dry woodland areas, ''D. isabelliana'' in ''

Pinus canariensis ''Pinus canariensis'', the Canary Island pine, is a species of gymnosperm in the conifer family Pinaceae. It is a large, evergreen tree, native and endemic to the outer Canary Islands of the Atlantic Ocean. Description ''Pinus canariensis'' is ...

'' woodland and open disturbed areas, ''D. sceptrum'' in the cloud zone community ''Clethro-Laurion'' (Sjogren 1972) near streams on steep slopes, and ''D. chalcantha'' in Canary Island

laurel forest Laurel forest, also called laurisilva or laurissilva, is a type of subtropical forest found in areas with high humidity and relatively stable, mild temperatures. The forest is characterized by broadleaf tree species with evergreen, glossy and el ...

Pollination

The flowers of ''Isoplexis'' species appear to be adapted for

bird pollination Ornithophily or bird pollination is the pollination of flowering plants by birds. This sometimes (but not always) coevolutionary association is derived from insect pollination (entomophily) and is particularly well developed in some parts of the w ...

. It was once thought that the original pollinators of ''Isoplexis'' and the other Canarian bird pollinated plants (such as members of the genera '' Canarina'' and '' Lotus'') were

sunbird Sunbirds and spiderhunters make up the family Nectariniidae of passerine birds. They are small, slender passerines from the Old World, usually with downward-curved bills. Many are brightly coloured, often with iridescent feathers, particularly i ...

s which had become extinct on the Canary Islands; this might explain why ''Isoplexis'' species are rare and considered

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...

(Vogel 1954; Vogel et al. 1984; Valido et al. 2004). However more recent work has shown that these plants are adequately pollinated by non-specialist flower visiting birds, particularly the Canary Islands chiffchaff (''Phylloscopus canariensis''), and the Canary Sardinian warbler ('' Sylvia melanocephala leucogastre'') (Olesen 1985, Ollerton et al. 2008), and in fact show some specific adaptations to infrequent pollination by these birds, such as extended flower lifespans (Ollerton et al. 2008), and a

hexose In chemistry, a hexose is a monosaccharide (simple sugar) with six carbon atoms. The chemical formula for all hexoses is , and their molecular weight is 180.156 g/mol. Hexoses exist in two forms, open-chain or cyclic, that easily convert into ...

-dominated sugar ratio in the composition of the nectar (Dupont et al. 2004). File:Isoplexis canariensis - Berlin Botanical Garden - IMG 8784.JPG, ''Digitalis'' (''Isoplexis'') ''canariensis'' File:Isoplexis isabelliana - Berlin Botanical Garden - IMG 8781.JPG, ''Digitalis'' (''Isoplexis'') ''isabelliana''

References

*Some of this text has been modified from Toomey, N. (2004). "Investigation of the phylogenetic utility of Cycloidea-like genes in various angiosperm lineages". PhD thesis. University of Reading, England. *Brauchler, C.; Meimberg, H. & Heubl, G. (2004). "Molecular Phylogeny of the genera ''Digitalis''. L and ''Isoplexis'' (Lindley) Loudon (Veronicaceae) based on ITS- and trnL-F sequences". ''Plant Systematics and Evolution''. 248 (1-4) 111-128. *Bentham, G. (1835). In: ''Edwards's Botanical Register''. (Lindley, J.). Vol. 21 pp. , ind.ad 1770 1 June 1835, London *Carvalho, J. A. S. S. (1999). "Systematic studies of the genera ''Digitalis'' L. and ''Isoplexis'' (Lindl.) Loud. (Scrophulariaceae: Digitaleae) and conservation of ''Isoplexis'' species". PhD thesis, University of Reading, England *Dupont, Y. L.; Hansen, D. M.; Rasmussen, J. T. & Olesen, J. M. (2004). "Evolutionary changes in nectar sugar composition associated with switches between bird and insect pollination: the Canarian bird-flower element revisited". ''Functional Ecology''. 18 670-676. *Heywood, V. H. (1972). "Flora Europaea: notulae systematicae ad floram Europaeam spectantes no. 13. Scrophulariaceae: ''Digitalis'' L. Sect. Macranthae Heywood, sect nov." ''Botanical Journal of the Linnean Society''. 65 (4): 357. *Himmelbaeur, W. & Zwillinger, E. (1927). "Biologische-chemische Formenkreise in der Gattung ''Digitalis'' L." ''Biologia Generalis''. 3 595-684. *Lindley, J. (1821). ''Digitalium Monographia''. H. H. Bohte, Londini, pg 27. *Linnaeus, C. (1753). ''Species Plantarum''. Vol II 561–1200. Impensis Laurentii Salvii, Holmaniae. *Loudon, J. C. (1829). ''Encyclopaedia of Plants''. 528 528-529. *Olesen, J. M. (1985). "The Macaronesian bird-flower element and its relation to bird and bee opportunists". ''The Botanical Journal of the Linnean Society''. 91: 395-414. *Ollerton, J.; Cranmer, L.; Stelzer, R.; Sullivan, S. & Chittka, L. (2008)
"Bird pollination of Canary Island endemic plants"
''Nature Precedings''. *Sjögren, E. (1972). "Local climatic conditions and zonation of vegetation on Madeira". ''Agrronomia Lusitana''. 36 (2) 95-139. *Valido, A.; Dupont, Y. L. & Olesen, J. M. (2004). "Bird-flower interactions in the Macaronesian islands". ''Journal of Biogeography'' 31: 1945-1953. *Vogel, S. (1954). "Blütenbiologische Typen als Elemente der Sippengliederung". ''Botanische Studien (Jena)''. 1: 1-338. *Vogel, S.; Westerkamp, C.; Thiel, B. & Gessner, K. (1984). "Ornithophilie auf den Canarischen Inseln". ''Plant Systematics and Evolution'' 146: 225-248. *Webb, P. B. (1845). ''Histoire Naturelle des Isles Canaries'' 3 (2-3): 144. *Werner, K. (1960). "Zur nomenklatur und taxonomie von ''Digitalis'' L." ''Botanische Jahrbucher fur Systematic, Pflanzengeschichte und Pflanzengeographie''. 79 (2): 218-254. *Werner, K. (1962). "Die kultivieten ''Digitalis''" Arten. Feddes Repertorium. 70: 167-182. *Werner, K. (1964). "Die verbreitung der ''Digitalis''. Arten. Wiss. Z. Martin-Luther Univ. Halle-Wittenberg, Math. Naturwiss. Reihe 13: 453-486. *Werner, K. (1965). "Taxonomie und phylogenie der gattungen ''Isoplexis'' (Lindl.) Benth und ''Digitalis'' L. ''Feddes Repertorium'' 70: 109-135. *Werner, K. (1966). "Die wuschformen der gattungen ''Isoplexis'' (Lindl.) Benth. und ''Digitalis'' L." ''Botanische Jahrbucher fur Systematic, Pflanzengeschichte und Pflanzengeographie''. 85 (1): 88-149. *Wettstein, V. (1891). "Scrophulariaceae. Rhinantoideae-Digitaleae". In: ''Die Naturlichen Pflanzenfamilien'' IV 3b (Engler, A. & Prantl, K. Eds.) pp. 83–90. Wilhelm Engelmann, Leipzig. {{Taxonbar, from=Q15975133 Isoplexis Endemic flora of Macaronesia Taxa described in 1821