Wood and stem anatomy of Petiveria and Rivina (Caryophyllales); systematicimplications

Petiveria and Rivina have been placed by various authors close to each othe r within Phytolaccaceae; widely separated from each other but both within P hytolaccaceae; and within a segregate family (Rivinaceae) but still within the order Caryophyllales. Wood of these monotypic genera proves to be alike in salient qualitative and even quantitative features, including presence of a second cambium, vessel morphology and pit size, nonbordered perforatio n plates, vasicentric axial parenchyma type, fiber-tracheids with vestigial ly bordered pits and starch contents, narrow multiseriate rays plus a few u niseriate rays, ray cells predominantly upright and with thin lignified wal ls and starch content, and presence of both large styloids and packets of c oarse raphides in secondary phloem. Although further data are desirable, wo od and stem data do not strongly support separation of Petiveria and Rivina from Phytolaccaceae. Quantitative wood features correspond to the short-li ved perennial habit of both genera, and are indicative of a xeromorphic woo d pattern.