Isoetes - Isoetaceae

Isoetes alstonii C.F.Reed & Verdc.

Photo: P. Ballings

Photo: P. Ballings

Photo: P. Ballings

Photo: P. Ballings






Common name


Pseudo-corm 1-2 cm in diameter, 2-lobed; bud scales vestigial or lacking. Leaves 10-40, linear, 130-400 mm × 1 mm (apically)- 13 mm (at base),apex tapering to a point, yellow to midgreen, semi-circular in cross-section, abruptly ovate-oblong at the base, with broadly hyaline wing, stomata present in upper parts of the leaves. Ligule 1-3 × c. 1.5 mm, hyaline, triangular, pointed. Velum very narrow, reduced to a thin marginal ring. Sporangia 4-16 × 3-6 mm, oblong to ellipsoid, drying black and shiny. Megaspores of 2 sizes, 0.52 and 0.3 mm in diameter, dark grey, drying white, usually 3-radiate, with large warts below, granulated above. Microspores winged, reticulate.


I. alstonii is distinguished from other species in our region by its 2-lobed pseudo-corm and a sporangium that is blackish when wet.


alstonii: named after A.H.G. Alston (1902-1958), Britisch botanist specialised in African pteridophytes.


Damp pockets of soil along streams, at the edges of pools, in seasonally dry streambeds and pools, perennial in permanent mist spray of the Victoria Falls, small temporary waterholes in wooded grassland.

Distribution worldwide

Africa, Madagascar.

Distribution in Africa

Ethiopia, Mozambique, Namibia, Tanzania , Zambia, Zimbabwe.

Growth form



  • Burrows, J.E. (1990) Southern African Ferns and Fern Allies. Frandsen, Sandton. Pages 36 - 37. (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 72 - 73. (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 316. (Includes a picture).
  • Hedberg, I; Friis, Ib & Persson, E (2009) Lycopodiaceae to Pinaceae.Flora of Ethiopia and Eritrea, vol.1 Page 18. (Includes a picture).
  • Jacobsen, W.B.G. (1983) The Ferns and Fern Allies of Southern Africa. Butterworths, Durban and Pretoria. Pages 154 - 155. (Includes a picture).
  • Kornas, J. (1979) Distribution and ecology of the Pteridophytes in Zambia. Polska Akademia Nauk Wydzial II Nauk Biologicznych. Page 35.
  • Reed, C.F. & Verdcourt, B. (1965) Isoetes alstonii, a new species of Isoetes from Rhodesia.Kirkia, 5(1) Pages 19 - 20. Protologue (Includes a picture).
  • 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 8.
  • Schelpe, E.A.C.L.E. (1970) Pteridophyta.Flora Zambesiaca, 0 Page 30. (Includes a picture).
  • Verdcourt, B. (2005) Isoetaceae.Flora of Tropical East Africa, Pages 6 - 7. (Includes a picture).