Often can two or more types be found within one plant. The unilacunar node system is the most common type among primitive seed plants. Vascular systems with five traces are most likely primitive, those with more or less traces are derived. Steles with leaf traces that run through one or a few internodes before branching into the leaf petioles can be regarded as primitive, those that run through many internodes as derived. A helical arrangement of the leafs of seed plants is regarded as primitive.
Monocots provide a highly specialized exception.
The vascular bundles of monocots seem to be scattered across the whole stem, being slightly more concentrated at the periphery. If the course of a single axial bundle is examined, a clear helical arrangement can be detected. Never is a vascular bundle exclusively central or peripheral. Depending on where the stem is cut, can it sometimes be found in the centre and sometimes in the periphery. At regular distances branch leaf traces.