A very hardy stonecrop
Lanceleaf stonecrop is a wonder. It's adaptations to harsh conditions include a poison that keeps herbivores from eating it. But it is food for Rocky Mountain apollo butterfly caterpillars. The plant produces more poison when anything starts eating it. The caterpillars' tolerance is limited. The caterpillars eat for about a half hour, then move to another plant before they get too toxic. This way both do OK.