PENTAPHRAGMA - A UNIQUE WOOD AND ITS SIGNIFICANCE

Qualitative and quantitative data are given for wood anatomy of three species of Pentaphragma (Pentaphragmataceae); the woods of the three s pecies are very similar. Pentaphragma is rayless, but eventually devel ops rays in at least one of the species studied. This is interpreted a s related to secondary woodiness or upright habit within a predominant ly herbaceous phylad. The vessel elements of Pentaphragma have feature s universally interpreted as primitive in dicotyledons: scalariform pe rforation plates with numerous bars; pit membrane remnants in perforat ions; scalariform lateral wall pitting; the genus also has fiber-trach eids with prominently bordered pits. These character states accord wit h the basal position in Campanulales accorded Pentaphragmataceae by Co sner et al. (1992), and suggests that order may have begun with more n umerous primitive features than generally recognized. The presence of occasional scalariform perforation plates, often aberrant, in secondar y xylem of families of Asterales sensu lato - Campanulaceae, Pentaphra gmataceae, Valerianaceae, and even Asteraceae (e.g., certain Lactuceae ) - can be attributed to paedomorphosis, extending these plates into s econdary xylem from primary xylem. Raylessness in Pentaphragma can be described in terms of secondary woodiness or paedomorphosis. The fact that fiber-tracheids are shorter than vessel elements in Pentaphragma is believed related to raylessness also, because some fiber-tracheids are produced from 'potential' ray areas.