The lianas of the Paullinieae tribe (Sapindaceae) have highly specialized stems which present four different structural variations of the vascular cylinder: divided, compound, corded and fissured. Because each vascular cylinder grows in an independent manner through its own circular cambium, we ask which type should be used for anatomic descriptions of the wood in these lianas. The corded, divided and fissured type variants appear only when the stems are in secondary growth. In the divided and fissured types, any cylinder may be used but in the corded type the central cylinder is recommended because the peripheral cylinders appear only in very mature stems. However, because the variant having a compound vascular cylinder appears in the stem when in primary growth and has a central vascular cylinder plus 2–10 peripheral cylinders, we analyzed the central vascular cylinder and three peripheral vascular cylinders of six species of Serjania to establish a standard. While it was found that the vascular cylinders are qualitatively homogeneous, quantitative differences did occur in a random fashion, either between the central and peripheral cylinders or among the peripheral cylinders. Based on statistical evidence, we conclude that the central vascular cylinder of the compound type should be used as standard in comparative anatomy studies.