Okay, it's simple. It's a rigid plant-like structure that occurs only on the island. It doesn't really flower, but instead in its maturity becomes more rigid and takes on a red hue. This red hue is an adaptation to warn the denizens that it's also quite poisonous, causing the body temp to rise if consumed and lead ultimately to death. The points also ward off anyone that attempts to eat/pick these plants.
It was rumored that red flowers were the cause of the boiling blood condition, but this was misconstrued due to lack of widespread education of the plants aside from flowers themselves and the information was mixed up. In truth, it's these spiky plants that result in "blood boiling" death.
And I totally just made that up. Make sense?