[6] [7] Analysis of the morphology and anatomy of the stigmarian systems suggests that the axes around the structure were shoot-like, and so they are called rhizomes or rhizomorphs.

[4] Stigmaria had a complex branching structure; thus, it is comparable to the rhizomes of the extant (living) relative, the quillworts (genus Isoetes).

Along the rhizomorph axes, the appendages are connected to each axis in a circular pattern which would shed during the growth stage, forming the helical arrangements of Stigmaria root abscission areas.

Tracheids of the secondary xylem are formed in spiral lines and consist of scalariform wall thickenings, while the fibrils are similar to those in the aerial branches.

The scalariform tracheids along the stigmarian rhizomorph axes had lateral vascular and cork cambium as evidenced by its secondary xylem and meristematic tissues.

Moreover, the spiral structure of the stigmarian rootlet attachment is separate from the asymmetrical changes of roots and rhizomes commonly seen in modern plants.

The stigmarian rootlets have a similarity to arborescent lycophytes, with functions related to absorbent organs, branching, and forking of proximal axes.