Geranium cuneatum subspecies tridens, or "silver geranium," is the most common species of geranium at Haleakalā. Its small silvery leaves, like the silversword, are covered with silky hairs that reflect sunlight and preserve moisture. The three triangular teeth on the leaf edges give it the name "tridens" -i.e. tri (three)-dent (teeth). You can see the silver geranium at the Headquarters Visitor's Center, along the Hosmer Grove Nature Trail, and in many other places in the shrubland.
Heralded as the "geranium capital of the world" by botanists, the high slopes of Haleakalā National Park are home to four species of Hawaiian geraniums found nowhere else on earth. These rare and unique plants are known as 'hinahina ("silver") or nohoanu ("cold-dwelling") in Hawaiian.
Geranium multiflorum, or "manyflowered geranium," has delicate pink, purple or white flowers that are pollinated by the native Hawaiian yellow-faced bee. The leaves are often tinged red, possibly an adaptation to protect them against the harsh alpine sun. These endangered plants are found in high-altitude grasslands and forests, and sometimes in the shrubland. You can see Geranium multiflorum planted at the Headquarters Visitors Center.
Geranium arboreum is the rarest of the four, and is the only bird-pollinated geranium in the world! The beautiful curved red flowers are adapted to fit the bill of nectar-sipping native honeycreepers like the i'iwi, who pick up pollen on their foreheads and transfer it to other flowers. Once widespread across the lower slopes of Haleakalā, this critically endangered species is now restricted to nine isolated populations with fewer than 50 individuals. Park staff are actively growing and planting these endangered plants in moist, shady gulches where they thrive. You can see the sprawling stems of Geranium arboreum along the Hosmer Grove Nature Trail.
Geranium hanaense is a rare, sprawling geranium found in high-altitude bogs on the eastern slopes of Haleakala. Geranium hanaense may represent an evolutionary transition-its silvery toothed leaves resemble Geranium cuneatum, while its white and purple flowers resemble Geranium multiflorum. Geranium hanaense was only recently discovered in 1988, and is in the process of being listed as an endangered species.