Salvinia adnata Desv.

Global description

Salvinia adnata is an aquatic, mat-forming, free-floating fern with horizontal stems, up to 25cm long. The fronds borne on short stalks, are arranged along the stems in threes, two unwettable floating leaves and a submerged leaf at each node. The floating leaf-like fronds are ovate with a cordate base, 7 to 40 mm long and 7 to 25 mm wide, pale green to greenish brown, frequently overlapping and folded along the midrib. Their upper surfaces are covered with water-repellent waxy hairs. These hairs (1-3 mm long) are arranged in distinct rows and are tipped with distinctive egg-beater shaped structures that aid buoyancy. The lower surface only has simple hairs near the midrib. The third frond is submerged in water, root-like and slender, up to 30 cm long and covered with fine brown hairs.

First leaves

First fronds ovate to obovate, fleshy, truncate or cordate at base and apex rounded to obtuse. They measure 1.5 cm long and 0.8 cm wide. The upper surface is covered with hairs associated forming small cages. They are arranged in whorls of 3 leaves, 2 green in surface and 1 lower surface immersed

General habit

Salvinia adnata is a floating fern, annual or vivacious, branched and slim floating rhizome, measuring up to 30 cm long. Rapid growth, it forms dense mats.

Underground system

It is a plant without roots.

Stem

Plants produce slender, branching runners and form mats of vegetation very quickly. These slender stems (1-2 mm thick) are much-branched and grow up to 30 cm long (usually only 6-25 cm long) before separating to form new plants. The length of stem between the joints (nodes), that is the internode length, varies depending on the density of the weed. When plant density is low the 'internode' length is relatively long, but as plant density increases, the 'internode' length may become very short.

Leaf

Fronds are simple in whorls of 3. Two of them are floating and green. The third is immersed is divided into many filaments similar to roots whose role is to draw the nutrients in the water. Floating fronds are carried by a short petiole false. They are oval oblong, base cordate and deeply emarginate apex. They measure 38 mm long and 25 mm wide. The upper surface is covered with hair compounds, formed by the juxtaposition of four that diverge uniseriate hairs then joined to form a structure shape of small cage. The underside is glabrous except for a few simple hairs along the center crease. Submerged filamentous fronds are dark brown and measure up to 4 cm long. They are covered with hairs.

Inflorescence

The central filaments submerged fronds, fertile, are sporocarps which are globose, indehiscent, staggered in pairs along the filament and covered with short hairs. Those of the base are smaller females. The subsessile ones are male. They are surrounded by a thin indusium globose attached to the base of the cylindrical receptacle.

Fruit

Salvinia plants are usually sterile. If sporocarps (spore bags) are formed they are 2-3 mm long and borne in clusters along the root-like leaves. Spores, when produced, are not viable.

Origin

Salvinia adnata is native to South America (south-eastern Brazil, Argentina).

Worldwide distribution

The species is now widespread in all continents America, Europe, ASia, Africa, Australia, Pacific islands.