Pentastemonaceae

The taxonomic position and rank of the only genus Pentastemona has been under discussion since Van Steenis (1982) described the genus in the Stemonaceae. Dahlgren et al. (1985) found it highly distinctive and suggested it worthy of family rank. Later on more material of P. sumatrana and P. egregia has become available facilitating a more accurate description of the androgynoecium. Conspicuous differences from the Stemonaceae, viz. the inferior ovary, the five pouches caused by the fusion of connectives and stigma (especially well-developed in P. egregia), the berry-like fruit and the exotesta (sarcotesta) of the seed, warranted the distinction of a separate new family for the genus. Note — Pentastemona is the first genus in the Monocotyledons with normally regular 5-merous flowers. Checked on abundant material, occasional flowers with 4 or 6 perianth lobes and stamens occur in both species.