Some of the driest land in the Everglades is pineland (also called pine rockland) ecosystem, located in the highest part of the Everglades with little to no hydroperiod. Some floors, however, may have flooded solution holes or puddles for a few months at a time. The most significant feature of the pineland is the single species of South Florida slash pine (Pinus elliottii). Pineland communities require fire to maintain them, and the trees have several adaptations that simultaneously promote and resist fire.[61] The sandy floor of the pine forest is covered with dry pine needles that are highly flammable. South Florida slash pines are insulated by their bark to protect them from heat. Fire eliminates competing vegetation on the forest floor, and opens pine cones to germinate seeds.[62] A period without significant fire can turn pineland into a hardwood hammock as larger trees overtake the slash pines.[63] The understory shrubs in pine rocklands are the fire-resistant saw palmetto (Serenoa repens), cabbage palm (Sabal palmetto), and West Indian lilac (Tetrazygia bicolor). The most diverse group of plants in the pine community are the herbs, of which there are two dozen species. These plants contain tubers and other mechanisms that allow them to sprout quickly after being charred.[64]