One of 2 basic morphologies of steles, the other being siphonostele. Protosteles are the more primitive, being characterized by a single strand of xylem in the centre of the stem or root, and lacking a pith. Protosteles can be subdivided into actinostele, hypophloic haplostele, haplostele, and solenostele. Compare dictyostele and monostele.
Subjects: Plant Sciences and Forestry.