Rocky Mountain Thistle Cirsium perplexans Also known as: Spring Thistle Phil Nyland, USFS biologist per Taxonomy Division:Magnoliophyta | - Flowering plants Family:Asteraceae Genus:Cirsium Species:Cirsium perplexans Growth CharacteristicsLife Cycle:PerennialGrowth Habit:Forb/herbHeight:3-4 ftLight Requirements:Full SunDrought Tolerance:HighBloom Months:may, jun, jul, augBloom Colors:Red, Purple Native Range United States: Colorado Keystone Species RankingBee Keystone: ★★☆☆☆ Based on number of native bee species using this genus for pollen and nectar (Source: National Wildlife Federation) Soil RequirementsSoil Type:sandy, well-drained, nutrient-poor soilpH:6.0 - 7.5 (slightly acidic to neutral)Drainage:excellent drainage requiredMoisture:dry to moderateNotes:native to dry, open habitats in Colorado