A big thank you to Lotus J. aka ngawangchodron@Flickr for today's image shared via the BPotD Flickr Group Pool (original image). Much appreciated!
I've previously featured Monotropa uniflora on BPotD. This photograph is a good complement to the previous one, since it shows a more typical habitat – the plant pushing through the duff of a coniferous forest floor. Lotus also asked in the Flickr posting why the plants have a pinkish tone. Reading through some of the local field guides, I noted that this isn't unusual; the colour of the plants is described as ranging from waxy-white to pinkish. However, I don't have an answer to the question of variation. I can think of four possible reasons: soil pH, the fungal species it is associated with, genetic variability or the soil's nutrient composition. It could be any or none of what I think it might be. Please feel free to suggest other ideas or, ideally, cite a scientific paper that has examined the question.
Great question about pigmentation. I didn't find anything definitive with a quick literature search, but this reference does offer an idea, namely anti-herbivory:
Leake, J. R. 1994. The Biology of Myco-Heterotrophic (Saprophytic) Plants. New Phytologist 127:171-216.
The relevant section follows:
"Bohm & Averett (1989) hav studied the flavonoids in five species of Monotropaceae in N. America. They found that Monotropa hypopitys and Pterospora did not contain detectable concentrations of the pigments and, in the others (Hemitomes, Sarcodes, and M. uniflora), flavonoids are present in low concentrations and are represented by simple compounds as has been reported for the Pyrolaceae, and in contrast to the Ericaceae. In the Monotropaceae, the pigments and tannins appear to be mainly confined to epidermal cells (Copeland 1938, 1938), which may explain prominence despite their low concentrations.
The production of anthocyanins and other astringent pigments in plants may play an important role in preventing grazing of shoots. Since flowering typically exhausts reserve carbohydrates in the plants, the selection pressures in favor of anti-herbivory compounds would be expected to particularly great...There is evidence that production of pigments is initiated by light, probably through phytochrome-regulated flavonoid synthesis (Kulemeier, Green & Chua, 1987)."
I have a PDF of the entire reference if anyone is interested in perusing the whole thing. It is pretty interesting stuff!
There is an article on the Monotropa uniflora, in Tom Volk's Fungus of the Month for october 2002. He has a good article relating to the role of the mycorrhizal fungi and the tree species that are involved. Another article by M. I. Bidartondo and T. Bruns Extreme specificity in epiparasitic Monotropoideae (Ericaceae: widespread phylogenetic and geographical structure Molecular Ecology (2001) 10, 2285-2295
This relates to the geographic distribution of Monotropoideae.
Thanks Justine and Mike! I hadn't considered that they might be grazed.