Floating herbs, often forming a dense mat over still waters, rhizome fine, horizontal, freely branching, hairy, rootless, protostelic. Leaves in whorls of 3, 2 leaf-like and floating, the other finely divided, submerged and rootlike, floating leaves papillose with hairs in groups of 4 above, smooth with solitary hairs below. Sporangia borne in sporocarps, the sporocarps on the branches of the root-like leaves, enclosed in a thin indusium, the sporocarps of 2 types, microsporocarp with many small microsporangia each with many microspores, megasporocarp with a few megasporangia, each containing a single megaspore; spores globose, trilete.
A monogeneric family of possibly 10 species, from most of the warmer parts of the world. Salvinia molesta is the sole species in Papuasia.
Small, free-floating, aquatic ferns, capable of rapid vegetative reproduction by fragmentation and forming a carpet on still water. Rhizome horizontal, freely branching, bearing uniseriate, muticellular hairs, lacking roots, vascular system a poorly developed, medullated protostele. Leaves shortly stipitate, in wholes of 3, 2 leaves of each whorl entire, broadly round-oblong, and floating on the water surface, costate with simple veins anastomosing at the margin, papillate above, the papillae bearing 4 muticellular hairs, often apically united, smooth with straight multicellular hairs below; the third leaf finely dissected into a cluster of long thin branches bearing numerous uniseriate multicellular hairs, submerged and root-like; vernation straight. Sporangia borne in sporocarps, the sporocarps in groups on the branches of the root-like leaves, quite enclosed in a thin globose indusium bearing multicellular hairs, receptacle much-branched, bearing either megasporangia or microsporangia; megasporangia few, large, each containing a single megaspore, microsporangia many, small, each containing 64 microspores. Spores globose, trilete.
Distribution: An almost pantropical and warm-temperate genus of about 10 species, represented in Papuasia by a single introduced species.
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.
Herzog, R. 1935. Ein Beitrag zur Systematik der Gattung Salvinia. Kritische Betrachtung der bisherigen systematischen Gliederung der Gattung. Hedwigia 74: 257 - 284.
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. Salviniaceae)
Kleinschmidt, H.E. 1973. Salvinia is a plant to watch. Advisory Leaflet 1181: 1 -2. Queensland Dept. Primary Industry. (reprinted from Qld. Agric. J. 1973)
Loyal, D.S. & Grewal, R.K. 1966. Cytological study on sterility in Salvinia auriculata Aublet with a bearing on its reproductive mechanism. Cytologia 31: 330 - 338.
Mitchell, D.S. 1972. The Kariba weed: Salvinia molesta. Brit. Fern Gaz. 10:252 - 252.
Mitchell, D.S. 1978b. The distribution and spread of Salvinia in Australia. Proc. 1st Conf. Counc. Aust. Weed Sci. Socs., Melbourne, 12 - 14 April. 321 - 326.
Mitchell, D.S. 1979. The incidence and management of Salvinia molesta in Papua New Guinea. Office of Environment & Conservation & Dept. Primary Industry, P.N.G. I - vi, 1 - 51, f. 1 - 2, 15 pl.
Mitchell, D.S. 1979b. Aquatic weeds in Papua New Guinea. Sci. in New Guinea 6:154 - 160, 15 pl.
Reed, C.F. 1954. Index Marsileales et Salviniales. Bol. Soc. Brot. 2 ser. 5 - 61.
Reed, C.F. 1965. Distribution of Salvinia and Azolla in South America and Africa in connection with studies for control by insects. Phytologia 12: 121 - 130.
Richards, A.H. 1979. Salvinia in the Sepik River. Harvest 5: 239 - 242. (PNG Dept. Primary Industry)
Stanley, T.D. 1979. Aquatic plants of Queensland. Five common free floating aquatics. Advisory Leaflet 1427: 1 - 7 . Queensland Div. Plant Industry. (reprinted from Qld. Argic J. 1978.)
Thorpe, J.P. 1978. Information paper on Salvinia molesta. Papaua New Guinea, Dept. Prim. Ind., Div. Fisheries. Roneo.
Weatherby, C.A. 1937. A further not on Salvinia. Amer. Fern J. 27: 98 - 102.
A single introduced species in Papuasia:
Three growth forms depending on nutrient, light and crowding: high nutrients, deep shade and uncrowded water produces small plants with leaves to c. 8 x 15 mm, spaced along the stem and not overlapping; open situations on uncrowded water produces larger plants with leaves c. 25 x 35 mm, not overlapping; in crowded situations the plants are very stout with leaves folded vertically, to c. 40 x 60 mm, the apex is notched and the leaves are highly overlapping; the leaves in all cases bearing fine simple hairs beneath and above with 4 hairs on protuberances uniting at the tip to form a hollow cage. Sporocarps borne along 2 - 4 branches 2 - 5 cm long, originating at the end of the rooting leaf-stalk, ovoid, 1.5 - 2 cm long, densely covered with pale, thin-walled hairs, containing early sporangia.
Habitat: Slow moving or still lakes, ponds, or backwaters at low to middle altitudes. Once introduced into a water body, rapid vegetative growth enables the plant to quickly cover most of the free water surface. In Papuasia it occurs from sea level to 1500 m altitude.
Distribution: The complex from which Salvinia molesta is derived is originally from South America, but has been introduced by man to Africa, India, Malaysia, Indonesia, the New Guinea mainland, Australia, New Zealand and Fiji. In Papuasia the greatest infestations are in the Sepik river.
Notes: This species is considered to be a pentaploid form of the Salvinia auriculata Aublet complex. Although sporocarps are produced, genetic incompatibility blocks the formation of spores, and as a result the sporangia are nearly all empty, or contain only few aborted spores (Loyal & Grewel 1976; Mitchell 1979). Thus the dispersal of this species is purely by vegetative means.
Like Azolla (see there) the leaves are totally water repellant on the hairy upper surface, and when forced under water the plants will immediately refloat the right way up. Andrews and Ellis (1913) showed that these hairs were positively chemotactic, in that egg applied to the leaves produced discolourations. The implication is that insects dying on the the leaves will be decomposed and the nitrogen compounds absorbed in much the same way as Drosera and other insectivourous plants.
Salvinia was probably introduced into New Guinea in the late 1970ís as an aquarium plant. It was released, or escaped, into the lower regions of the Sepik River and ponds in the Wau Valley. In the Sepik, introduced perhaps a year or so earlier, it has spread alarmingly into the lakes, blocking access, killing fish etc., and making the area generally unihabitable for the villagers there. The Wau population is persistent, but so far has only affected two ornametal lakes. In 1980 there was an outbreak on the Waigani swamp but this subside, due to natural causes. The Fly and Strickland rivers have not been effected by Salvinia, although there have been unconfirmed reports of it existence in the upper Fly river areas. With increased activity there, an introduction of the species is very likely; this would be disastrous in still water bodies such as Lake Murray.