[3] The leaves have three well-developed groups of supporting tissue inside, giving them a firm texture.

[2][4] They are usually bordered by a narrow rim, with some of the cells being noticeably thicker and a yellowish-brown in colour.

[4] While the species in this genus typically have white spores, those of Isoetes stellenbossiensis have a distinctive greenish tinge and become darker when exposed to water.

[4] They are protected by black bud scales with three horny, prong-like teeth.

[3] This quillwort can form large colonies of thousands of individuals when conditions are suitable.

[4] It may even be found growing with highly drought tolerant species such as Crassula undulata, Aristea africana, and Oedera fruticosa.

[3] An assessment conducted by the South African National Biodiversity Institute in 2020 classified this species as least concern as, while this species was still declining, the assessors believed that the population was still common enough with large enough subpopulations to not be at immediate risk of extinction.