In a white pine, hemlock, and oak woods in New Hampshire, we searched for lady slipper orchids, Cypripedium acaule. They had been reported there earlier in the week.
We didn’t find any there, but based on a tip we found four at a nearby intersection. From the US Forest Service: “In order to survive and reproduce, pink lady’s slipper interacts with a fungus in the soil from the Rhizoctonia genus. Generally, orchid seeds do not have food supplies inside them like most other kinds of seeds. Pink lady’s slipper seeds require threads of the fungus to break open the seed and attach them to it. The fungus will pass on food and nutrients to the pink lady’s slipper seed. When the lady’s slipper plant is older and producing most of its own nutrients, the fungus will extract nutrients from the orchid roots. This mutually beneficial relationship between the orchid and the fungus is known as “symbiosis” and is typical of almost all orchid species.” There’s more at the link, on the bees who pollinate them, and why picking them is so destructive.
Share
This work by Matthew Wills is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.
Backyard and Beyond 
Your Lady’s Slipper photos are outstanding. The last time I saw any they were found on a walk down a very shaded hiking path up in the Shenandoah Mountains. I haven’t seen any since.
An English Girl Rambles
I enjoyed your post and have recently taken an interest in growing lady’s slippers in my gardens. I planted a yellow variety a few weeks ago. I’m unsure if the symbiotic situation is necessary for all lady slipper orchids but the purchase was made with a goodly amount of the soil the plant had been growing in and the plant looks well to this point