Molecular data place Hydnoraceae with Aristolochiaceae

Area of Science:

• Plant Systematics
• Molecular Phylogenetics
• Angiosperm Evolution

Background:

• The phylogenetic position of the holoparasitic Hydnoraceae family has been a long-standing controversy in angiosperm classification.
• Previous studies have been unable to definitively place Hydnoraceae within the broader angiosperm tree.

Purpose of the Study:

• To resolve the phylogenetic position of Hydnoraceae among angiosperms using molecular data.
• To investigate the evolutionary relationships between Hydnoraceae, Aristolochiaceae, and related families.

Main Methods:

• Obtained nuclear SSU and LSU rDNA, and mitochondrial atp1 and matR sequences for Hydnora and Prosopanche.
• Performed combined phylogenetic analyses using maximum parsimony with nuclear, mitochondrial, and chloroplast genes (rbcL, atpB).
• Analyzed three datasets with varying numbers of genes and taxa, including coded missing data for plastid genes absent in Hydnoraceae.

Main Results:

• Molecular phylogenetic analyses consistently support the monophyly of Hydnoraceae.
• Hydnoraceae forms a clade that is strongly associated with Aristolochiaceae sensu lato (including Lactoridaceae).
• This clade is sister to Piperaceae and Saururaceae, and molecular data do not support a close relationship with Rafflesiaceae.

Conclusions:

• Molecular phylogenetics provides a robust placement for Hydnoraceae within the Piperales or a closely related order.
• While Hydnoraceae and Aristolochiaceae share morphological similarities, their precise taxonomic relationship requires further resolution.
• Current data suggest Hydnoraceae should not be grouped with Rafflesiaceae, challenging traditional classifications.