Trithuria

Trithuria is a genus of minute aquatic herbs. It is the only genus in the family Hydatellaceae. In 2008, the genus Hydatella was subsumed into Trithuria. In that paper, some species were merged and some new species were described, raising the number of species in Trithuria to 12. Eleven of the 12 species were formally described. The single species from India was not covered.^[1]

These diminutive, moss-like, aquatic plants are the closest living relatives of the two closely related families Nymphaeaceae (water-lilies) and Cabombaceae.^[2] Together, these three families compose the order Nymphaeales in the APG III system of flowering plant classification. Trithuria (Hydatellaceae) diverged from the rest of Nymphaeales soon after Nymphaeales diverged from its sister taxon, which comprises all of the flowering plants except the two orders Nymphaeales and Amborellales.

The placement of Trithuria in Nymphaeales was a surprise to some but this position is supported by ten morphological synapomorphies:

• lack of a vascular cambium,
• lack of pericyclic sclerenchyma,
• anomocytic stomata,
• truncate anther connective,
• boat-shaped pollen,
• inner integument with two cell layers,
• palisade exotesta,
• seed operculum formed by cell enlargement in the inner integument,
• perisperm and
• hypogeal germination.^[3]

References