Calandrinia is a genus of flowering plants known as purslanes and redmaids. It includes 37 species of annual and perennial herbs which bear colorful flowers in shades of red to purple and white. Species of this genus are native to the Americas, including western and southern South America, Central America, and western North America.[1][2] Some species have been introduced to parts of Australia, New Zealand, southern Africa, Asia, and Europe.[1] Over 60 species native to Australia and New Guinea that were formerly included in Calandrinia are now placed in a separate genus, Rumicastrum or Parakeelya.[3] A single eastern Australian species named in 2022, Calandrinia petrophila, is still included in Calandrinia, but will be placed into the Australian genus when the name of the new genus is finally settled.[4]
Species in the genus Calandrinia are annual or perennial herbaceous plants with a sprawling or erect habit. The leaves are mostly basal and may be either alternate or opposite in arrangement. Flowers are produced in cymes. Each flower produces between four and eleven petals, though often five. Flowers may be white, purple, pink, red, or yellow.[5][6][7]
The genus Calandrinia was erected in 1823 by German botanist Carl Sigismund Kunth.[8][9] It was named for Jean Louis Calandrini (1703–1758), a Genevan botanist.[6]
Approximately 74 Calandrinia species are native to Australia.[10] Along with the pigweeds (Portulaca species), Calandrinia are the most prominent succulent species in Australia.[11] The Australian Calandrinia were traditionally considered to be monophyletic (share the same ancestry) with 14 Calandrinia species from the Americas, and are still classified as belonging to the same genus.[12] However, in 1987 Australian taxonomist Roger Carolin proposed that the American and Australian Calandrinia are not closely related to each other based on morphological analyses. Follow-up studies also supported two different lineages, based in part on the absence of Calandrinia on islands along possible dispersal pathways between South America and Australia and in part on genomic data.[13][10]
Despite this, the nomenclature has not been officially changed for all Australian Calandrinia, including C. balonensis. Although the need for a nomenclature change is widely agreed, a debate has arisen over the appropriate naming of the Australian Calandrinia.[3] A proposal has been made to rename the genus as Parakeelya on the grounds that it is used as a common name for the whole genus, derives from South Australian and Central Desert Indigenous names, and is already accepted as a synonym for some Australian species.[14] The competing view holds that the Australian genus should be named Rumicastrum according to established nomenclatural rules.[3] Plants of the World Online accepts Rumicastrum.[15] The proposal to rename Calandrinia as Parakeelya has not yet been decided.[12]
The genus is classified in the family Montiaceae.[1] It was previously placed in the purslane family, Portulacaceae.[6]