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Isoetaceae

Submerged or emergent aquatic, sometimes terrestrial in moist places, herbs with a 2-5 lobed, corm-like rootstock, bearing a rosette of leaves, and dichotomous roots from between the lobes. Leaves linear and grass-like, with 4 longitudinal air-canals, and a single central vascular strand, expanded basally, glabrous, a small triangular ligule on the adaxial surface above the sporangium. Sporangia very large, borne adaxially in depressions at the base of the sporophylls, containing either large, trilete megaspores, or minute, monolete microspores, sometimes partially or entirely covered by a membranous vellum, extending down from the apex of the sporangium.

Distribution

A family of 2 genera (considered a single genus by many authors) of more or less cosmopolitan distribution, with over 125 species. Isoetes is the only genus in Papuasia and is represented by 5 species.

Literature

Alston, A.H.G. 1959. Isoetaceae. Fl. Males. ser. 2. 1: 62 - 64, f. 1.

Croft, J.R. 1980. A taxonomic revision of Isoetes L. (Isoetaceae) in Papuasia. Blumea 26: 177 - 190, f. 1, pl. 1 - 21.

Croft, J.R. 1985. Isoetaceae. In Leach, G.J. & Osborne, P.L., Fresh water plants of Papua New Guinea. Univ. P.N.G., Port Moresby. pp. 43 - 48.

Pfeiffer, N.E. 1922. Monograph of the Isoetaceae. Ann. Mo. Bot. Gard. 9: 79 - 218.

Genera in Australia and Papuasia

A single genus in Papuasia ... Isoetes (5)

Note

The Papuasian species are very closely related and present a clinal gradation of characters from west to east across the island of New Guinea. Wider studies of the genus as a whole may show that these taxa could be more appropriately treated as subspecies or varieties.


Updated November 1999 by Jim Croft (jim.croft@environment.gov.au)