Wood anatomy of Agdestis (Caryophyllales): systematic position and nature of successive cambia

Features in which Agdestis differs from Phytolaccaceae s. s. include presence of both libriform fibers and vasicentric tracheids (rather than one or the other); bands and strands of thin-walled apotracheal parenchyma (in addition to paratracheal scanty parenchyma}, and raylessness (also reported for Bougainvillea of Nyctaginaceae, a family close to Phytolaccaceae). Dimorphism in vessel diameter in Agdestis (narrow vessels like libriform fibers in diameter) is attributable to the lianoid habit. Packets of crystals coarser than typical for raphides occur idioblastically in Agdestis, as do raphides in Phytolacca. ln Phyto/acca and in other Phytolaccaceae, one finds an unusual feature that occurs in Agdestis: nonbordered simple perforation plates. Anatomical data support Agdestis as forming a monogeneric subfamily within Phytolaccaceae s. l. The nature of successive cambia in Agdestis is compared with those in other Phytolaccaceae and in Nyctaginaceae. A common pattern is probably present, although differences in terminology and observations obscure the pattern. The term "interxylary phloem" is a misnomer because conjunctive tissue is not secondary xylem as generally understood. After cessation of the cambium in the first cylinder, radial rows of cells form outside the phloem and inside the cortex; this activity may constitute a lateral meristem. Apparently within the radial rows of cells, successive cambia form; each of these cambia produce secondary phloem externally and secondary xylem internally. There is little or no cambial activity in interfascicular areas.