| In the Coal Measure period, however, the protostele was characteristic of one of the two main groups of ferns. |
| The anatomy was simple, the central strand of sclerenchyma of the algal progenitors becoming a strand of tracheids forming the earliest type of stele, the protostele. |
| The simplest and apparently most primitive type of stele is the protostele, in which the xylem is in the centre of the stem, surrounded by a narrow band of phloem. |
| In its simplest form it is called a protostele, and is to be found in both living and fossil plants. |
