Updated: Mar 23, 2019
The genus Hydrocotyle L. (commonly 'pennyworts') in the family Araliaceae has about 130 species worldwide, 57 of which occur in Australia. Though most of the species are perennial, there are 35 annual species, all of which are endemic to Australia. Many of these annual species occur in the Southwest Australian Floristic Region biodiversity hotspot. Annual species of Hydrocotyle are cryptic for most of the year, only being noticeable when flowering and fruiting following seasonal rains. Despite years of taxonomic interest, few molecular studies have been conducted on this enigmatic group of plants.
A new study by Andrew Perkins (Western Australian Herbarium) recently published in Molecular Phylogenetics and Evolution has been the first to reconstruct the phylogeny of Hydrocotyle sampling both annual and perennial species. The study sequenced nuclear and chloroplast molecular markers to reveal clades corresponding to annual or perennial life histories and the presence or absence of floral bracts. The monotypic genus Neosciadium was found to be nested within Hydrocotyle and sister to the clade of bracteate annual species. Relationships of morphologically diverse species and putative taxa in Western Australia were also resolved with the molecular data and morphological examinations. This study informs future research about the evolutionary history of Hydrocotyle across Australia and relations between species in South Australia, Asia and Australia.