William, it's true that I have not tested the soils where I have found Trillium nivale, and in addition, I only know it from two locations of the many that exist, even just here in Minnesota. As yet another concession, I did think Caulophyllum thalictroides only grew in acid soils only but apparently I was wrong. Yet I can't explain the presence of Hepatica americana (not H. acutiloba) in said plant communities if the soils were not even slightly acidic. Note that I did not say T. nivale would not do well in neutral or alkaline soil, only that I question whether it is a requirement. I wonder too, why the species is so much more prevalent in more easterly states of the USA that have more acidic soils than south and central Minnesota. I don't think we disagree here: I'm just saying that pH (and other environmental factors) are not as black and white (or as strict) as one may think. Many types of plants grow in the wild where they find niches within the ecosystems. These niches do not necessarily possess the conditions where they will grow best or are the only place they will grow, rather it is where they compete best in the wild. Take Tamarack (trees), Larix laricina, for instance. In the wild they are found in always wet sphagnum bogs, usually pH 4.0-4.5(5). But in cultivation, they grow much better, faster and larger in (drier) uplands with pH up to at least 7. Likewise, I use to grow many Chinese species lilies in heavy clay soil that easily cracked open in the summer as it dried out. Most experts would assume that would be certain death for these bulbs, yet because of other accompanying conditions, my lilies did just fine. Similarly, I contend that T. nivale grows in multiple environments.
Sorry if this was unclear, but if it was, I can always blame it on language difficulties 
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