Tetracarpaea

Tetracarpaea is the only genus in the flowering plant family Tetracarpaeaceae. Some taxonomists place it in the family Haloragaceae sensu lato, expanding that family from its traditional circumscription to include Penthorum and Tetracarpaea, and sometimes Aphanopetalum as well. Tetracarpaea has one species, Tetracarpaea tasmannica, an evergreen, bushy shrub from subalpine areas of Tasmania. It is variable in height, from 1.5 to 10 dm. The leaves are shiny and small, with prominent veins, and the ends of the branches are crowded with small, white flowers. It is not known in cultivation, but has been grown from cuttings. Tetracarpaea has an odd mix of characters, and during the nineteenth and twentieth centuries, its affinities remained obscure. It was variously classified by different authors, usually with considerable uncertainty. Molecular phylogenetic analysis of DNA sequences has shown that Tetracarpaea is a member of the Haloragaceae alliance, an informal group composed of the families Aphanopetalaceae, Tetracarpaeaceae, Penthoraceae, and Haloragaceae. These are four of the fourteen or fifteen families in the order Saxifragales. The following description is based on information from several sources. Tetracarpaea tasmannica is a glabrous, evergreen, erect and bushy shrub. It is variable in height, usually from 1.5 to 6 dm, but sometimes attaining a height of 1 m and a width of 7 dm. The leaves are elliptic to oblanceolate, about 25 mm long and 8 mm wide, on a petiole about 2 mm long. The veins are prominent and end near the margin. The margins are serrate or crenate. On both surfaces, the epidermis is covered by a thick cuticle. The inflorescences are dense, erect, terminal racemes, up to 5 cm long. The flowers appear in autumn. They are bisexual, actinomorphic, and 5 to 10 mm wide. The 4 sepals persist to the maturity of the fruit. The 4 petals are white and spatulate in shape. The stamens are either 4 or 8 in number. If 4, they are opposite (along the same radii as) the sepals. The anthers are basifixed.