THE MICHIGAN BOTANIST
THE MYCORRHIZAL SYSTEM OF
PTEROSPORA ANDROMEDEA (PINE-DROPS) IN
WEST MICHIGAN INFERRED FROM DNA SEQUENCE DATA
Jianhua Li*, Jeffrey Corajod, Holly Vander Stel, and Austin Homkes
Department of Biology
35 E 12th St., Schaap Science Center,
Holland, MI 49423
Pterospora andromedea is a mycoheterotrophic plant with a disjunct distribution between western and eastern North America and obtains carbon and nutrients indirectly from photosynthetic plants
via an ectomycorrhizal fungal bridge. In this study, we used DNA sequence data to determine the organisms involved in the system in West Michigan. Our results suggest that at least two photosynthetic plants (Tsuga and Acer) are the potential carbon source of the system and that Pterospora is
specifically associated with an unidentified species of subgenus Amylopogon of Rhizopogon. Previous studies have shown that seed germination of Pterospora relies on chemical cues from the fungus,
implying a dominant role of the fungus in the system. Our field observations suggest that repeated
branching of Pterospora roots increases the mass production of the fungal mycelia and lead us to
speculate that Pterospora may be a mutualistic partner, not a parasite or exploiter, in the mycorrhizal
KEYWORDS: Pterospora, nrDNA ITS, rbcL, mutualism, mycorrhizal, subgenus Amylopogon,
Pterospora andromedea Torr. (pine-drops) is a mycoheterotrophic plant relying on fungal host for germination, growth, and development (Bakshi 1959).
Molecular studies have shown its close relationship with other mycoheterotrophic plants in Ericaceae such as Monotropa, Allotropa, and Sarcodes
(Cullings 1994; Kron et al. 2002).
Pine-drops show a disjunct distribution between the eastern and western
North America with an extension in the west to northern Mexico (Bakshi 1959).
Albeit with a wide distribution, no more than a dozen plants have been seen in
one season of any area investigated (Bakshi 1959). This is also true in Michigan
where there are 43 occurrences each with a single or small number of individuals, and Pterospora has been listed as a State S2 threatened species in Michigan
(Higman and Penskar 1999).
Prior to Bakshi (1959) it had not been clear whether Pterospora is parasitic on
the roots of pine trees (Coulter and Nelson 1909; Piper and Beattie 1914;
Hutchinson 1926; Hylander 1939; Fernald 1950) or saprophytic (MacDougal
and Lloyd 1899; Jepson 1901; Henderson 1919; Rendle 1925; Copland 1941;
Benson 1957). Since there is no chlorophyll in Pterospora and its roots have not
been found to be organically connected with the roots of photosynthetic vascular
*Author for correspondence. E-mail: email@example.com, Phone: 616-395-7460, Fax: 616-395-7125.