Seasonal herbs, aquatic, subaquatic or terrestrial in moist places, rhizome creeping with well-spaced fronds, solenostelic, clothed with hairs. Leaves long and filiform without leaflets, or with 2 or 4 leaflets at the apex of a long filiform stalk, veins in the leaflets several times forked, free to the margin or casually anastomosing, glabrous or hairy. Sporangia borne in sori in sporocarps (conceptacles), with a single large megaspore or numerous minute microspores, both types in the same sorus, the sori in 2 rows in the sporocarp, the sporocarps solitary or in groups, axillary, or inserted on the petiole; spores trilete.
A cosmopolitan family of 3 genera with c. 70 species. So far, only a single species of Marsilea has been recorded from Papuasia.
Small aquatic or subaquatic ferns, rooting in mud and in areas subject to periodic inundation. Rhizome creeping, the fronds well-spaced, also on short lateral branches, roots borne at the base of the fronds, growing tip covered with fine hairs, solenostelic, the cortex with many large air cavities. Fronds very long-stipate, with 2 opposite pairs of leaflets, leaflets radially arranged and floating on the water surface (when inundated), often bearing muticellular hairs; veins several times forked, radial, +/- free, or anastomosing occasionally or at the leaflet margin only; vernation circinnate. Sporangia of 2 types, borne in discrete sori in sporocarps; the sporocarps pedunculate, axillary or basally on the petiole, solitary or in groups, hard and woody, often hairy, globose to ovoid, 2 small projections often present at the end of the stalk, splitting when mature; the sori exindusiate, elongate, borne in 2 rows on a gelatinous ribbon (sporophore) that elongates as the sporocarp opens, receptacles in a single row, bearing a single apical megasporangium and 2 lateral microsporangia; sporangia with a solitary megaspore or 32 - 64 microspores, annulus lacking, opening by decay of sporangial wall. Spores trilete, globose, ornamented, the megaspores with a distinct beak.
Distribution: A cosmopolitan genus of about 60 species, of which one is known from Papuasia.
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.
Johns, R.J. 1981. The ferns and fern-allies of Papua New Guinea. Part 6 - 12. P.N.G. Univ. Tech. Res. Rep. R 48-81. (incl. Marsileaceae)
Launert, E. 1968. A mongraphic survey of the genus Marsilea Linneaus. 1. The species of Africa and Madagascar. Senck. Biol. 49: 273 - 315.
Reed, C.F. 1954. Index Marsileales et Salviniales. Bol Soc. Brot. 2 ser. 5 - 61.
Tindale, M.D. 1953. Studies in Australian pteridophytes, No. 1. Contrib. N.S.W. Nat. Herb. 2:5 - 12. (Marsilea)
Represented in Papuasia by a single species:
Rhizome long-creeping with leaves spaced approximately 1 - 4 cm apart, periodically branching, main roots arising at the insertion of the leaves, or along the rhizome, sometimes on short side branches, bearing fine secondary roots to 5 mm long. Leaves with stalks 2 - 20 cm long, depending on the size and depth of immersion of the plant, blade of 4 +/- radial leaflets in 2 pairs, the pairs opposite and on short stalks less than 1 mm long, the leaflets rounded triangular, 5 x 5 to 25 x 25 mm, margin entire, glabrous, veins fine, radiating and several times dichotomous, casually anastomosing, uniting at the outer margin into a continuous vein almost on the margin. Sporocarps on stalks 3-5 mm long, inserted in groups of 1 -5 at the base of the leaves, sometimes on short side branches, flattened globose, 2 - 3 mm long, with 2 conical projections above the insertion of the stalk, smooth, covered with pale unicellular hairs.
Habitat: Flats beside rivers and seasonally inundated areas, in Papuasia from low altitudes below 50 m in areas with a prolonged dry season.
Distribution: The Philippines and the New Guinea mainland, there restricted to the area around Port Moresby, the Morehead River and border area of the Western Province and a single collection from Cape Vogel.
Notes: According to Copeland (1958 - 1960), Marsilea crenata is endemic to the Philippines. A wider geographic revision of the genus is required to show if the New Guinea material is indeed distinct.
This species is very infrequently collected in New Guinea, and its restriction to monsoonal areas indicate that fronds may die back in the dry season. Most species of this genus require a period of emergence in order to develop sporocarps.