Isoetes capensis

The cape quillwort is a tufted geophyte with horny toothed scales.^[2] It has between 5 and 35 leaves that bear sporangia. These are held at a 45-degree angle. This is unusual as most species have perpendicular leaves.^[3] These are slender (4 mm (0.16 in) at the base) and reach a length of up to 20 cm (7.9 in), with a heart-shaped appendage (ligule) at the base.^[2][3] The ligule is up to 1 mm (0.039 in) long and pale, although it is darker at the point of attachment.^[3] The sporangia are completely covered in a thin membrane.^[2] They have a diameter of 2–5 mm (0.079–0.197 in) and are oval or round in shape.^[3]

This species shows immense variability in its spores. The surface ranges from having irregular tubercules to interconnected ridges to being covered in a net-like structure of ridges. All of these surface sculptings may be found in a single population.^[4] They grey-white megaspores have a diameter of 0.39–0.57 mm (0.015–0.022 in).^[3]

This species has a three lobed pseudocorm. The dark brown leathery bud scales are triangular and have dimensions of about 3 by 3 mm (0.12 by 0.12 in). They may also have a hair that is about 3 mm (0.12 in) long.^[3]

The cape quillwort is endemic to the Western Cape of South Africa.^[5] It is found between Darling, Stellenbosch and Worcester and an altitude of up to 300 m (980 ft). It grows on sandy clay soils in low areas that experience seasonal flooding as well as around vleis.^[2] There are nine subpopulations with combined area of occupancy of 44–56 km² (17–22 sq mi).^[6] At least one specimen has also been recorded from Somerset West.^[7]