The establishment and survival of epiphytic orchids depend on factors such as the environmental conditions of the forest

American Journal of Botany 100(12): 1–10, 2013 ; http://www.amjbot.org/ © 2013 Botanical Society of America The establishment and survival of epiphytic orchids depend on factors such as the environmental conditions of the forest that sustain them and, perhaps most importantly, on the presence of appropriate fungi. Because orchid seeds are minute and contain few stored reserves, colonization of a seed by a compatible fungus is essential for germination and early seedling development ( Arditti and Ghani, 2000 ; Smith and Read, 2008 ). In epiphytic orchids, the stronger limitations to water and nutrients derived from their particular habitat may have increased the frequency of mycorrhizal associations that extend beyond the germination stage ( Martos et al., 2012 ). Knowing the identity of associated mycorrhizal fungi thus becomes an important task in orchid conservation strategies ( Batty et al., 2002 ; Dearnaley et al., 2012 ), especially when species require specifi c fungi ( McCormick et al., 2004 ). The identifi cation of orchid mycorrhizal fungi has been studied for a long time, and more recently DNA-based molecular techniques have been used ( Dearnaley et al., 2012 ). Orchids with different trophic strategies have been found to be associated with different groups of fungi ( Rasmussen and Rasmussen, 2007 , 2009 ). Mycoheterotrophic (MH) orchids are associated with a diverse group of Ascomycota or Basidiomycota fungi ( Bidartondo et al., 2004 ; Girlanda et al., 2006 ; Martos et al., 2009 ). However, autotrophic orchids generally associate with a limited range of Basidiomycota, mainly Agaricomycotina including members of Tulasnellaceae ( Suárez et al., 2006 ; Kottke et al., 2008 ), Sebacinales ( Kottke et al., 2008 ; Suárez et al., 2008 ), and Ceratobasidiaceae ( Otero et al., 2002 , 2007b ; Graham and Dearnaley, 2012 ). Nevertheless, Pucciniomycotina with members of Atractiellales have also been recently noted to form mycorrhizas ( Kottke et al., 2010 ). Concerning the type of habitat, both epiphytic and photosynthetic terrestrial orchid species have been reported to be associated mainly to Tulasnellaceae ( Martos et al., 2012 ). Previous studies have shown that “specifi city”, understood as the phylogenetic diversity of the fungi associated with a particular plant species ( Taylor et al., 2002 ), is diffi cult to predict. In the case of MH orchids, high specifi city has been reported between them and their fungal partners ( Taylor and Bruns, 1997 ; McKendrick et al., 2002 ; Selosse et al., 2002 , 2004 ; Bidartondo and Read, 2008 ; Barrett et al., 2010 ), while specifi city varies for photosynthetic orchids. Association with a narrow or even dominant group has been shown for many photosynthetic species, both terrestrial ( McCormick et al., 2004 , 2006 ; Shefferson et al., 2005 , 2007 , 2008 ; Roche et al., 2010 ; Swarts et al., 2010 ; Yuan et al., 2010 ) and epiphytic orchids ( Otero 1 Manuscript received 20 February 2013; revision accepted 3 September 2013. The authors thank C. Naranjo for his fi eld assistance, L. J. De Hond for her linguistic assistance, and the reviewers for valuable comments that helped to considerably improve the manuscript. This research was partially supported by the SENESCYT-ECUADOR. M. de la Cruz was supported by project grant CGL2009-13190-C03-02 of the Spanish Ministry of Science and Innovation. 5 Author for correspondence: (email: [email protected] )