Hemiparasitic interaction between Castilleja tenuiflora (Orobanchaceae) and Baccharis conferta (Asteraceae): haustorium anatomy and C- and N-fluxes

Background: Castilleja tenuiflora is a hemiparasite of Baccharis conferta. The haustorium is the characteristic structure of hemiparasitic plants and its anatomy varies depending several factors such as host species, position on the root and environment. Question: What is the structure and anatomy of haustoria builded in field interaction? Based on C, N and chlorophyll contents, is C. tenuiflora a facultative hemiparasite of B. conferta? Species studied: Castilleja tenuiflora Benth. and Baccharis conferta Kunth. Study site and dates: Plant materials were collected in the Iztaccihuatl-Popocatepetl National Park (N 19 degrees 0.5' 9.6 ", W 98 degrees 40' 24.2 ", 3,480 m.a.s.l.), State of Mexico, Mexico, in December 2013. Methods: Individuals of B. conferta and C. tenuiflora growing independently or in hemiparasite interactions were collected and samples were processed for anatomical and histochemical characterization, determination of C, N and chlorophyll. Results: Haustoria were globular and located mainly in the lateral roots of B. conferta. Anatomy of haustorium shows the characteristic structures: exophyte and endophyte. Haustorial tissues storage starch, tannins and essential oils while in the B. conferta roots also calcium oxalate crystals were found. C levels were significantly influenced by hemiparasitic interaction. This is the first study that characterizes a hemiparasitic interaction in the field and specifically between C. tenuiflora and B. conferta. Conclusions: Haustoria builded in interaction with B. conferta show the characteristic structure and anatomy. Hemiparasitic relationship represents for C. tenuiflora a source of C and other compounds such as essential oils.