Isoetes - Isoetaceae

Isoetes welwitschii A. Braun

Photo: JE. Burrows
South Africa






Calamaria welwitschii (A. Braun) Kuntze
Isoetes natalensis Baker
Calamaria natalensis (Baker) Kuntze

Common name


Small fern 5–20 cm tall. Pseudo-corm 3(-4)-lobed, scarcely developed or up to 1.5 cm wide; bud scales dark brown to black, triangular with the tip abruptly narrowed to a sharp point, up to 3 × 7 mm. Leaves 5-35, pale green, erect, slender, 50-350 mm × 4 mm at the base, abruptly enlarged to 2-6 mm wide in sporangial area, ± semi-circular in cross-section, apex awl-shaped. Dried specimens often rather distinctly bicolored, whitish at base (sporangial part and about 1.5 cm above it) contrasting with dark green upper parts. Ligule narrowly triangular, 2.5 mm long. Velum absent or rarely a rim ± 1 mm wide. Sporangia pale or ± dark, suborbicular, up to 2.5-7(-9)× 2-3.5(-5) mm. Megaspores of two sizes, about 0.45-0.56 mm in diameter, ash grey to white, distal surface tuberculate with smaller warts interspaced, proximal surface trilete with spaced tubercles confined to the centre or if more extensive then central ones the largest or sometimes ± smooth. Microspores minutely tuberculate.


Similar to I. schweinfurthii in which the warts on the distal face of the megaspores have concave sides which flare out at the base.


welwitschii: named after the Austrian botanist F. Welwitsch (1806-1872) who first collected this species.


Marshy or perennially wet seepage areas and vleis in grassland, black mud of pools and forest streams, on granite rock.

Distribution worldwide

Africa, Madagascar.

Distribution in Africa

Angola, Botswana, Central African Republic, Dem. Republic of Congo, Eritrea, Ethiopia, Ghana, Kenya, Nigeria, South Africa, Sudan and South Sudan, Tanzania , Zambia.

Growth form



  • Burrows, J.E. (1990) Southern African Ferns and Fern Allies. Frandsen, Sandton. Pages 34 - 36. (Includes a picture).
  • Crouch, N.R., Klopper, R.R., Burrows, J.E. & Burrows, S.M. (2011) Ferns of Southern Africa, A comprehensive guide. Struik Nature. Pages 68 - 69. (Includes a picture).
  • Fisher E. & Lobin W. (2022) The genus Isoetes (Isoetaceae) in Central Africa (DRC, Rwanda, Burundi) with the description of three new species.Willdenowia, 52 Page 330. (Includes a picture).
  • Jacobsen, W.B.G. (1983) The Ferns and Fern Allies of Southern Africa. Butterworths, Durban and Pretoria. Page 154.
  • Roux, J.P. (2009) Synopsis of the Lycopodiophyta and Pteridophyta of Africa, Madagascar and neighbouring islands. Strelitzia 23, South African National Biodiversity Institute, Pretoria. Page 11.
  • Roux, J.P. (2001) Conspectus of Southern African Pteridophyta.Southern African Botanical Diversity Network Report, 13 Page 30.
  • Verdcourt, B. (2005) Isoetaceae.Flora of Tropical East Africa, Pages 3 - 4.