7. Overall assessment of taxon's reproductive success: Seed set is high in 



one and possibly all Montana populations, but dispersal and recruitment may 

 be limiting factors in the narrow autumn window for dispersal and 

 establishment. 



Ecology of the taxon. 



A. General summary: Interspecific competition with other vascular plants and 

 obligatory mycotrophic symbiosis appear to be the most significant biological 

 interactions for the species. 



B. Positive and neutral interactions: The root system has little surface area for 

 adsorption and the species may have an obligate dependence on endomycorrhizae for 

 adsorption of phosphorus and water as well as carbohydrates at certain stages and at 

 some level. Blue green algae have also been noted within the roots of orchids. 



The symbiotic fiingi have been classified as members of the genus Rhizoctonia 

 (Wells 1981), considered a "taxonomic nightmare" (Zettler 1997) because most do 

 not produce stable forms with fruiting structures in pure cultures. More recent 

 taxonomic work has recognized three new general formerly included in Rhizoctonia 

 (Moore 1987), with the genus Epulorhiza most frequently associated with temperate 

 terrestrial orchids (Currah and Zelmer 1992). 



Part of the success of the Orchid Family may be ascribed to mycotrophic relation 

 (Zettler 1997). The symbiotic relation between fiingi and orchids has been examined 

 more closely in recent decades and some have concluded that it is a form of 

 parasitism on the part of the orchids, of little or no benefit to the fiingi. Fungal 

 hyphae proliferate within cortical cells forming extensive coils called "pelotons". 

 The orchids digest the pelotons at a controlled rate balanced between digestion and 

 re-infection, so that they are effectively "fungus managers" (Zettler 1997). This 

 symbiosis may be particularly critical during the underground seedling stage, during 

 the years in which mature plants remain belowground ("season-long dormancy" of 

 Lesica and Steele 1 994), and possibly at critical pheno logical stages in the season. 



It has been noted that more common species of orchids may serve as "refiigia" for the 

 symbiotic fiingi that sustain rarer orchid species of the same habitat (Zettler and 

 Hofer 1997), though the fungi may also live separate from orchids. Presence of the 

 northern bog orchid {Habenaria hyperborea) was documented at many sites of 

 Spiranthes diluvialis in Montana and rangewide (Appendix B), the most likely fungal 

 "refugia" if there is such a thing for its endomycorrhizae. 



Pollination by bumblebees may not be an obligate interaction, but results in greater 

 seed production as represented by fruiting capsule mass than does self-pollination 

 (Sipes and Terpedino 1995). 



38 



