Cracking the omega code: hydraulic architecture of the cycad leaf axis

The ancient order Cycadales (“cycads”), have a pattern of vascular bundles in the leaf axis, seen in transverse section as an inverted “omega”. In the genus Cycas, Tomlinson et al. recreate this system as a 3-dimensional pattern based on images of sequential sections.

Each leaflet is supplied by a single trace, from adaxial bundles, renewed by migration of abaxial bundles, which do not interconnect. Distal leaflets are not at a hydraulic disadvantage because they have a direct hydraulic supply. This approach provides a method for comparison with other extant genera, all of which show leaflets supplied by multiple vascular bundles.