Iris ser. Longipetalae is a series of the genus Iris, in Iris subg. Limniris.
William Rickatson Dykes in his book 'Handbook of Garden Irises' (of 1924) includes 4 species in his Iris longipetala subsection; including Iris longipetala (Herbert), Iris missouriensis Nuttall, Iris arizonica (Dykes, 1917) and Iris montana (Nuttall).[1] Iris arizonica and Iris montana have since been classified as synonyms of Iris missouriensis.[2]
The series was then first classified as a 'series' by Diels in 'Die Natürlichen Pflanzenfamilien' (Edited by H. G. A. Engler and K. Prantl) in 1930. It was further expanded by Lawrence in Gentes Herb (written in Dutch) in 1953.[3] [4]
There is still a lot of confusion within the series.
The British Iris Society only lists Iris missouriensis and classes Iris longipetala as a variant of Iris missouriensis.[5] The American Iris Society and Pacific Iris Society lists three species; Iris longipetala (Herbert), Iris missouriensis (Nuttall) and Iris pariensis (Welsh).[6] [7] [8] But Plant List regards Iris pariensis as a synonym of Iris missouriensis.[2] Iris pariensis was found by Stanley Larson Welsh in Utah and published in 'Great Basin Naturalist' 46(2): 256 in 1986.[9]
The series has species are native to western North America,[6] seen in Washington (state), Oregon and California.[10]
They prefer to have moisture in the spring and a dry period during the summer. They also do not like root disturbance hence they are difficult to grow as nursery plants. They are also rarely grown in the UK.[10] The species have thick rhizomes,[8] fruiting stems (that follow the flowers) that stay on the plant until the next growing season, (or longer)[6] [8] a stigma with 2 teeth (or lobes)[8] and seed capsules with 6 ribs and taper into points on the ends.[6] [8]