I'm pleased to report that a new version of Flora Conservanda has just been published - this time on the web.
Written from a regional perspective, Flora Conservanda: New England 2012 is the New England Plant Conservation Program (NEPCoP) list of plants in need of conservation. The list contains plants growing in New England that are globally rare, regionally rare, and locally rare. It also lists plants that are considered historic to New England (though they may exist elsewhere in the U.S. or world) and plants whose status in the region is yet undetermined but are believed to be rare. More research is needed to properly categorize these latter species.
1Brumback W.E., Mehrhoff L.J., et al. 1997. Flora Conservanda: New England. The New England Plant Conservation Program (NEPCoP). List of plants in need of conservation.