Salvinia [a complex consisting of Salvinia auriculata Aubl. [SAVAU], Salvinia molesta D.S. Mitch. [SAVMO], Salvinia biloba Raddi, Salvinia herzogii de la Sota][all are CDFA list: C][all are Federal Noxious Weeds] Photographs Maps
SYNONYMS: giant salvinia, karibaweed, African pyle or payal, butterfly fern, eared watermoss, aquarium watermoss, Salvinia hispida Kunth, Salvinia rotundifolia Willd., Salvinia natans auct. non (L.) All.
GENERAL DESCRIPTION: A complex of closely related perennial floating aquatic ferns that are difficult to distinguish from one another. Salvinia is often grown as an aquatic ornamental, but has escaped cultivation and become noxious in many regions worldwide. Depending on environmental conditions, plants exhibit a range of growth forms, from the primary invading form with small flat leaves to the tertiary or mat form with large, crowded, folded leaves. Under favorable conditions plants can form dense mats more than ½ m (2 ft) thick. Mats can limit recreational activities on lakes and waterways, increase flooding and stagnation, displace native plants and animals, and decrease water quality. Where it could be carefully managed, Salvinia has been used to remove excess nutrients and other pollutants from water. Dried plants make satisfactory mulch. Introduced from tropical South America. The salvinia weevil (Cyrtobagus salvinae) has been successfully used as a biocontrol agent in Africa and Australia. The weevil has been accidentally introduced into the Southern U.S.
MATURE PLANT: Stems horizontal just below water surface, sometimes branched. Leaves 3-whorled, with 2 floating, 1 submerged. Floating leaf upper surfaces densely covered with water-resistant egg-beater-shaped hairs ~ 2-4 mm long that diverge into 4 branches near the top and fuse together at the tips. Floating leaves of the primary form are flat, well spaced, +/- oval with slightly lobed bases to obovate with wedge-shaped bases, ~ 8-15 mm wide. Tips rounded or acute. Floating leaves of the tertiary form are densely crowded, tightly folded upwards along the midvein, deeply 2-lobed at the tip, ~ 25-60 mm wide when unfolded, typically broader than long. Floating leaves of the secondary form are intermediate to the primary and tertiary forms. Submerged leaves are root-like, whitish, finely dissected into several filaments up to 2 cm long with hair-like projections along the length.
ROOTS and UNDERGROUND STRUCTURES: True roots lacking.
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REPRODUCTIVE STRUCTURES: Variable. Some filaments of submerged leaves may develop chains or clusters of tiny ovoid spore-bearing structures (sporocarps) ~ 1-3 mm in diameter.
POSTSENESCENCE CHARACTERISTICS: Partial plant death often stimulates dormant buds to develop.
HABITAT: Still and slow-moving waters of lakes, ponds, reservoirs, rivers, marshes, ditches, rice fields. Grows best in nutrient-rich water in tropical climates. Tolerates mild temperate conditions, some salinity, and occasional frost, but not prolonged periods of freezing temperatures. Dense mats do not develop at temperatures below 10º C (50º F).
DISTRIBUTION: Salvinia molesta has escaped cultivation and is spreading in the Southern U.S., particularly Texas, and as far west as the lower Colorado River in Arizona and California. At publication time, populations have naturalized in the Colorado River drainage and have invaded some canals in the Sonoran Desert (Imperial Co.). Salvinia is sometimes offered for sale as an aquatic ornamental. Introductions may be expected to persist wherever water hyacinth is established.
PROPAGATION/PHENOLOGY: Reproduces vegetatively by stem fragments. Each node has up to 5 dormant buds. Older stems separate from nodes as more buds develop. Fragments disperse primarily with wind, water currents, flooding, and human activities. Some protected dormant buds of mat-form plants can survive dry conditions for long periods, up to 2 years in one case. Salvinia molesta and S. herzogii are functionally sterile hybrids. The other 2 species can develop fertile spores. Under optimal conditions, plants can double their biomass in as little as 2-3 days.
MANAGEMENT FAVORING/DISCOURAGING SURVIVAL: Removing and destroying fragments from boat propellers, docking lines, fishing gear, and other equipment can help prevent the spread of salvinia.
SIMILAR SPECIES: Unlike innocuous Salvinia species, potentially noxious salvinia has egg-beater-shaped hairs ~ 2-4 mm long on the upper surfaces of floating leaves that are easiest to see on young leaves growing under sunny conditions. Hairs can become damaged on old leaves or may not develop on shaded plants.
CONTROL METHODS:
Prevention: Salvinia species have spread via contaminated aquatic plant stocks, by water craft transport between bodies of water, by moving water, and by sale and exchange of Salvinia plant material. The current limited distribution of Salvinia makes prevention the most feasible strategy for limiting its spread.
Mechanical: Complete removal of Salvinia by mechanical harvest is very difficult and costly on large infestations. Plants may regenerate from small fragments and rapidly reinfest cleared areas.
Chemical: Some herbicides which have been used to control giant salvinia include Diquat at 1-2 kg/ha, fluridone at 20 parts per billion, diquat at 3% plus copper at 5%. All of these herbicides and herbicide combinations provided good to excellent control in Salvinia. Large scale applications of herbicides may result in a rapid loss of oxygen from water bodies due to the exceedingly large amount of dead plant material that sinks to the bottom.
Biological: The weevil Cyrtobagous salviniae has been highly successful in dramatically reducing Salvinia molesta infestations in several countries worldwide. However, the weevil has not been successful against S. auriculata. Additional research is being conducted to better understand the Cyrtobagous complex in relation to specificity on Salvinia species.