Large yellow petals 3-4.5 cm long and a stigma with four branches in an X are used to identify this showy flower. The blooms are on an un-branched stem 1.5 to 2.5 m high. Typically found at elevations below 6000 feet, this one was seen at Hetch Hetchy. Hooker's Evening-primrose got its common name from its earlier scientific name, Oenothera hookeri, after Sir Joseph Dalton Hooker (1817-1911). Hooker was the Director of the Royal Botanical Gardens at Kew in England. He came to Yosemite in 1877 and collected over 1,000 plants in the Sierra Nevada mountains and Western United States. He was a great friend of Charles Darwin and was in support of the latter's controversial Theory of Evolution.