I’m one generation removed from being able to tell you stories of running through cow pastures and stepping on field thistles (“but we kids didn’t whine in those days, we never noticed them”). However, I suspect even my leather-footed aunts and uncles would have purposefully veered away from whitespine thistle, which, as plasmodiafiend points out, is the most heavily-armed native thistle in North America. Of course, unless they had lived in a very specific area of Nevada, they would never have encountered it.
Cirsium clokeyi is endemic to the Spring Mountains, Nevada. Population surveys during the 1990s pegged the number of plants at under ten thousand individuals in total, distributed in an area with a maximum dimension of 13.1 km (8.1mi). As is often the case, the long-term survival of this species is tied in with the fates of others: two local butterfly taxa, the Spring Mountains comma skipper (a subspecies of Hesperia comma) and the Nevada admiral (Limenitis weidemeyerii nevadae) are pollinators and nectar-feeders.
The source of much of today’s information is this rare plant factsheet on Cirsium clokeyi (PDF) from the Nevada Natural Heritage Program. This herbarium specimen scan is one of the few other bits of interestingness about this species I could track down in my limited time today.