New insights in the long-debated evolutionary history of Triuridaceae (Pandanales)

- Triuridaceae most likely descended from the second major split in Pandanales.
- Tribes within Triuridaceae (Triurideae, Sciaphileae, and Kupeaeae) are monophyletic at current taxon sampling.
- Triuridaceae have longer branch lengths than other Pandanales taxa for analyzed nuclear and mitochondrial DNA regions.
- Crown age of Triuridaceae is between 50 and 90 Ma, corresponding to a Lower Eocene to Upper Cretaceous origin.
- The split-up of Gondwana possibly had an influence on evolution of Triuridaceae.

The mycoheterotrophic plant family Triuridaceae (Pandanales) is hypothesized to be an old family, mainly based on its pantropical distribution. The existence of fossils from the Upper Cretaceous, assigned to Triuridaceae may form additional support for a great age of the family, although the affinity of these fossils to Triuridaceae is questioned. Although the circumscription of Triuridaceae has never been problematic, probably due to its distinct morphological characters, its systematic relationship has been under debate since the family was described around 1840. The lack of synapomorphies suitable for resolving higher taxonomic relationships is a function of the family's reduced vegetative growth and the highly modified floral structures. Molecular studies have assigned Triuridaceae to Pandanales, but its exact phylogenetic position remains unknown. In the present study the phylogeny of the Pandanales was reconstructed using four molecular markers and the divergence age estimates were obtained with a relaxed molecular clock method. We found that Triuridaceae are monophyletic and most likely descent form the second major split in Pandanales. The relationships between the other Pandanales families (Cyclanthaceae, Pandanaceae, Stemonaceae and Velloziaceae) are otherwise in accordance with earlier studies. Velloziaceae are sister to the rest of the Pandanales, Stemonaceae are most likely sister to a clade consisting of Pandanaceae and Cyclanthaceae, and the latter two families are sister to each other. All currently recognized tribes within Triuridaceae are also monophyletic at current taxon sampling. We estimate that the family has a Cretaceous (or Lower Paleocene) stem age, which is in accordance with earlier predictions. This old age, along with elevated mutation rates indicated by long branch lengths and the family's mycoheterotrophic lifestyle, might account for the substantial morphological differences between Triuridaceae and its closest relatives.