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ISOETACEAE

Submerged or emergent aquatic, sometimes terrestrial in moist places, herbs with a 2-5 lobed, corn-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 ver 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.

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.

Isoetes L.

Terrestrial or submerged aquatic herbs with several to numerous leaves, arising in an imbricate rosette from the apex of a 2 - 5 lobed, flattened, corn-like rootstock that may accumulate lobes of large quantities of dead overlapping tissue, the roots dichotomous, arising from between the lobes. Leaves sessile, simple, linear to linear-triangular, generally apically terete, flattened or angled basally, at the very base broadly winged and expanded and broadly attached to the rootstock, the mesophyll divided into 4 longitudinal, septate cavities, a single unbranched vein in the tissue between the cavities. All leaves potentially sporophylls, the sporangia very large, solitary, broadly adnate in an adaxial basal cavity, thin-walled and irregularly septate, annulus lacking, dehiscing by decay of the sporangial walls; a membranous vellum extending down form the apex and attached to the sides of the sporangial cavity, partially or entirely covering the sporangium or lacking; a small triangular ligule arising from a cavity immediately above the sporangial cavity. Sporangia of 2 types: megasporangia containing large, granular, trilete, variously sculptured or smooth megaspores; microsporangia containing minute, powdery, monolete, smooth to spinulose microspores.

Notes: The aquatic species of Isoetes in Papuasia are all found in the same habitat; rooted in the peat or fine silt sediments of alpine tarns or lake margins from 2800 to 3900 m altitude, mostly above 3300 m. They can withstand a certain degree of exposure and hav e been collected serveral times from almost dry pools or lake margins. A form of Isoetes neoguineensis has been collected from running streams and future collections may show that the other species are capable of existing in this habitat.

Distribution: A more or less cosmopolitan genus of c. 75 species. There are 5 species in Papuasia, restricted to the New Guinea mainland; I. hopei is terrestrial and the remaining 4 are obligate aquatics:

References

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. Ferns and Fern Allies, in Leach, G.J. & Osborne, P.L. 1985. Freshwater Plants of Papua New Guinea. 33 - 74, f. 6 - 13, pl. 5 - 7.

Croft, J.R. (in press).

Fuchs, H.P. 1962. Nomenclatur, Taxonomie und Systermatik der Gatung Isoetes Linneus in geschichtlicher Betrachtung. Beih. Nova Hedwigia. 3: 1 - 103.

Marsden, C.R. 1979. Morphology and taxomony of Isoetes in Australasia, Northeast and Southeast Asia, China and Japan. Unpubl. PhD. Thesis, University of Adelaide. I—viiii, 1—185, f.1—347.

Pfeiffer, N.E. 1922. Monograph of the Isoetaceae. Ann. Mo. Bot. Gard. 9: 79 - 232.

Reed, C.F. 1953. Index Isoetales. Bol. Soc. Brot. 27: 5 - 72.

Although the following key relies very heavily on the appearance of the megaspores, the megaspores are quite large (c. 0.5 mm across) and the differences can be readily seen with a hand lens. In any case, the known populations are strongly isolated geographically. It should be noted that these species are very closely related, and a wider study of the genus may show that they should be considered as subspecies or varieties; it is postulated that they represent the remnants of a more or less continuous cline that may have existed during the Pleistocene for earlier when the range of habitats was more continuous (Croft 1980, and in prep.).

1 Megaspore ornamentation finely and irregularly rugulose, appearing almost smooth at low magnification; leaves genarlly 2 -3 mm wide at the middle. Mt Wilhemina (Mandala) and Star Mts... I. habbemensis
Megaspore ornamentation reticulate, of even or irregular relief; leaves generally 1 - 3 mm wide at the middle... ... 2
2 Megaspore ornamentation shallowly or moderately pronounced reticulate of even relief lower than or equal to that of the trilete ridge; leaves 2 -3 mm wide at the middle... ... 3
Megaspore ornamentation deeply reticulate generally of uneven relief as high as the trilete ridge, often appearing warty; leaves 1 -2 mm wide at the middle. Owen Stanley range... I. neoguineensis
3

Megaspore ornamentation of shallow relief less than the trilete ridge. Mt Giluwe...

I. stevensii
Megaspore ornamentation as pronounced as the trilete ridge. Mt Saruwaged... I. frigida

 

Isoetes frigida Croft [ined.]

Synonym: Isoetes stevensii auct. non Croft: Croft (1980).

Rootstock 3-4-lobed, leaves to 5-18 cm long, 2-3 mm wide at the middle, with a wide base broadly dilated to c. 10 mm wide, broadly attached over 10 mm to the rootstock, pale yellow to white basally grading to dark green apically, the basal part winged, flat to slightly concave or convex adaxially, rounded abaxially, the distal half +/- teret, apex acute; stomata absent; ligule broadly deltoid, 1 - 1.5 mm wide. Sporangia elliptic, oblong or ovate, to 8 x 3 mm, cream to pale brown, velum absent, megaspores white, c. 0.5 mm diameter, the surface regularly reticulate or honeycombed, the reticulations pronounced and of very even relief; microsporangia sparsely dark punctate, microspores minute, brown when dry.

Distribution: So far only known from around a single small lake on the southern side of Mt Saruwaged. Further collecting may find it in other permanent tarns on the Saruwaged and Bangeta massifs.

Specimens examined

Morobe: Mt Saruwaged, Croft 1300, 1301, Hoogland 9846

Isoetes habbemensis Alston

Rootstock ( 2 - ) 3 ( -4) - lobed, leaves to c. 15 (-30) cm long, 2 - 3 mm wide at the middle, with a wide base broadly dilated to c. 10 mm wide, broadly attached over 15mm to the rootstock, pale yellow to white basally grading to dark green apically, the basal part winged, flat to slightly concave or convex adaxially, rounded abaxially, the distal half +/- terete, apex acute; stomata absent; ligule broadly deltoid, 1 - 1.5 mm wide. Sporangia elliptic, oblong or ovate, to 10 x 4 mm, cream to pale brown, velum absent, megaspores white, c. 0.5 mm diameter, the surface irregularly low-wrinkled and warty, less so on the proximal surfaces; microsporangia sparsely dark punctate, microspores minute, brown when dry.

Distribution: The western half of the Central cordillera from Mt Wilhelmina (Mandala) in Irian Jaya, to the Snow Mountains and Mts Scorpion and Auriga of the Star Mountains in Papua New Guinea, 3200 - 3300 m altitude.

Specimens examined

Irian Jaya: Lake Habbema, Brass 9440 (Type), 9441
West Sepik: Star Mts, Mt Scorpion, Croft 56, Croft & Lelean in LAE 65873, Veldkamp 6548

Isoetes neoguineensis Bak.

Synonym: Isoetes neoguineensis Bak. var. rheophila Croft

Rootstock 3 - 4 ( - 5)-lobed, leaves to c. 10 - 20 (-35) cm long, 1 - 2 mm wide at the middle, with a wide base broadly dilated to 10-15 mm wide, broadly attached over 15 mm to the rootstock, pale yellow to white basally grading to dark green apically, the basal part winged, flat to slightly concave or convex adaxially, rounded abaxially, the distal half +/- terete, apex acute; stomata absent; ligule broadly deltoid, 1 - 1.5 mm wide. Sporangia elliptic, oblong or ovate, to 3 - 6 x 6 - 11 mm, cream to pale brown, velum absent, megaspores white, c. 0.5 mm diameter, the surface irregularly reticulate or honeycombed, highly pronounced with very uneven relief, the proximal surfaces appearing warty; microsporangia sparsely dark punctate, microspores minute, brown when dry.

Distribution: Scattered on the major peaks the full length of the Wharton Range of the Owen stanley ranges of eastern New Guinea, from Mt Strong to Mt Victoria, 2800 - 4000 m altitude.

Notes: When originally collected, the specimens from a flowing river on the Neon Basin, Mt Albert Edward, were of such a vastly different form to any other specimens of the genus in Papuasia that they were assigned to a separate variety, var. rheophila. Subsequent collections (Croft in press) have revealed intermediates between the two extremes so the variety can no longer be maintained, a decision foreshadowed by Marsden (1979).

Specimens examined

Central: Mt Strong, Coode & Stevens in NGF 46201, 46254; Stevens & Coode in LAE 51360; Mt Dickson, Hartley TGH 13001; Mt Albert Edward, Craven 2717, Croft 1412, 1413, 1414, 1451, Croft & Lelean in LAE 61483, Kanai 753570, Kores in WEI 1569; Neon Basis, Mt Albert Edward Croft in LAE 62486, 61486, 61531, Croft & Marsh 1450; Mt Scratchley, Giulianetti s.n. (Type), Coode & Stevens in NGF 46337; Mt Victoria, Craven 3069, Craven 3070, Croft in LAE 61775

Isoetes stevensii Croft

Rootstock (2 - ) 3 ( - 4)-lobed, leaves to c. 10 (-20) cm long, 2 - 3 mm wide at the middle, with a wide base broadly dilated to c. 10 mm wide, broadly attached over 10 mm to the rootstock, pale yellow to white basally grading to dark green apically, the basal part winged, flat to slightly concave or convex adaxially, rounded abaxially, the distal half terete, apex acute; stomata absent; ligule broadly deltoid, 1 - 1.5 mm wide. Sporangia elliptic, oblong or ovate, to 6 x 4 mm, cream to pale brown, velum absent ,megaspores pale grey to white when dry, c. 0.5 mm diameter, the surface regularly low reticulate and honeycomb-like, less so on the proximal surfaces; microsporangia sparsely dark punctate, microspores minute, brown when dry.

Distribution: Restricted to the high alpine areas of Mt Giluwe, 3400 - 3600 m altitude.

Specimens examined

Southern Highlands: Mt Giluwe, Coode et al. In NGF 40229, Croft & Marsh 708, Pullen 2883, van Royen 11264, Schodde 1915, 1843, 1843a, Stevens & Foreman in LAE 52251 (Type), Wade & Mc Vean in ANU 7756