I make it a point to never publicly disclose the locations of my photographs of rare species of any variety (animal, or plant). I often see overzealous photgraphers taking photos from as close as they possibly can to their subject without realizing the damage they're causing. I attended a lecture by Marilyn Light, last month, that emphasized the importance of not coming closer than 2 or 3 feet from any orchid, due to the compaction of the soil it causes and the effect that has both on the roots of the existing plant and the possible germination of future generations of plant. I remember seeing a 4 foot tall, multiple stemmed Cyp reginae in a bog in a MN state park that was entirely surrounded by footprints. Needless to say, it's not present above ground, this season.
The most unfortunate example of the danger of listing known populations of rare species is one that I've noticed the last couple years. The state of Minnesota lists populations of many of their rare species. There is a native lady slipper that has it's strongest presence in Minnesota (Cypripedium candidum). It has already been extirpated from many of its previous locations, even in the last couple decades, from invasive grasses and degradation and alteration in hydrology. There is a site in the Minnesota River valley where, a few years ago, thousands of Cyp candidum grew. The last two years there have been no more than a dozen plants and these were all single stemmed plants. This didn't happen naturally and this year, I saw physical evidence of poaching of these and Cyp parviflorum at the site (numerous shovel holes). I called the Department of Natural Resources to report the poaching. They were appalled, but said that with how thinly the conservation officers are stretched, there's basically no way the problem can be stopped, unless the offenders are caught in the actual act of poaching, with plants in hand.
It's a terrible thing to see and will likely be more and more common with the advent of sites like Flickr, where people list and even map the locations of their photographs.