eustele

However, it is really just a variant of the eustele.

There is also a variant on the eustele found in monocots like maize and rye.

The vascular system itself curiously resembles that of the vascular plants' eustele, which evolved convergently.

In addition to being found in stems, the eustele appears in the roots of monocot flowering plants.

The Mississippian-aged lyginopteridaleans tended to have a simple protostele usually surrounded by secondary wood, but in later forms there was a eustele with a central core of pith or mixed-pith.

The relatively slender stems (fossil genus Callistophyton) had a eustele with a well-developed zone of secondary wood, and unlike most (but not all) other Palaeozoic pteridosperms, showed axillary branching.

The vascular bundles in a eustele can be collateral (with the phloem on only one side of the xylem) or bicollateral (with phloem on both sides of the xylem, as in some Solanaceae).