R. fluitans Lam was applied to this plant in NZ. However R. fluitans has longer leaves and often larger flowers (Johnson and Brooke 1989).
Vascular – Exotic
Herbs - Dicotyledons other than Composites
The National Vegetation Survey (NVS) Databank is a physical archive and electronic databank containing records of over 94,000 vegetation survey plots - including data from over 19,000 permanent plots. NVS maintains a standard set of species code abbreviations that correspond to standard scientific plant names from the Ngä Tipu o Aotearoa - New Zealand Plants database.
Submerged perennial plant with creeping rhizomes and long leafy stems. The leaves are usually 3 to 6 cm long, forked and ending in threadlike segments. The white 5-petalled flowers with a yellow centre are held above the water surface.
Widely naturalised, common in many regions but apparently absent in Northland and very rare in Westland. Becoming rare in northern New Zealand south to the volcanic plateau where it is still common.
Moderately fast flowing to still water bodies.
Wetland plant indicator status rating
Information derived from the revised national wetland plant list prepared to assist councils in delineating and monitoring wetlands (Clarkson et al., 2021 Manaaki Whenua – Landcare Research Contract Report LC3975 for Hawke’s Bay Regional Council). The national plant list categorises plants by the extent to which they are found in wetlands and not ‘drylands’. The indicator status ratings are OBL (obligate wetland), FACW (facultative wetland), FAC (facultative), FACU (facultative upland), and UPL (obligate upland).
OBL: Obligate Wetland
Almost always is a hydrophyte, rarely in uplands (non-wetlands).
Aquatic perennial, rarely terrestrial; roots all fibrous. Rhizome creeping. Stems slender to stout, prostrate or ascending, up to 1-(2)m long often rooting at the nodes. . Lvs divided into many filiform segments, glabrous but for a few short hairs at segment tips, (1)-3-6-(8) cm long; segments narrowly linear in terrestrial plants; petiole (2)-5-30 mm long. Fls solitary, 8-15 mm diam. Pedicels terete, glabrous, (2)-3-6-(8) cm long. Sepals 5, bluish near tip, reflexed 2.5-4 mm long. Petals 5, white with yellow base, 6-8 x c. 4mm long; nectary single, 0.5-1mm from petal base, lunate. Receptacle usually with a few sparse hairs at base, elongating slightly at fruiting. Achenes 30-60, glabrous, ovoid, slightly flattened, transversely rugose; body 1.5-2 mm long; beak straight, c. 0.5 mm long.
Fanwort (Cabomba caroliniana) and egeria (Egeria densa) have similar flowers. Differs from fanwort in that the leaves are not fan-shaped and alternately rather than oppositely arranged. Differs from egeria in that the leaves are finely divided, forked and not arranged in whorls.
(October) December - February (April)
Spreads by seeds or stem fragments. Bird dispersed seed.
Temperate Northern Hemisphere and Australia
Reason for introduction
Possibly naturally introduced from Australia by water fowl. Not known from the international aquarium or pond trade (Kasselmann 2003).
Not usually controlled in New Zealand, but may be controlled manually, or mechanically.
ranunculus: From the Latin ‘rana’ frog, meaning little frog and probably refers to the plants typical marshy habit where frogs abound
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA). Features description from Webb et al. (1988).
References and further reading
Webb, C.J.; Sykes, W.R.; Garnock-Jones, P.J. (1988). Flora of New Zealand Volume 4: Naturalised pteridophytes, gymnosperms, dicotyledons. Botany Division, DSIR, Christchurch. 1365 pp.
Champion et al (2012). Freshwater Pests of New Zealand. NIWA publication. http://www.niwa.co.nz/freshwater-and-estuaries/management-tools/identification-guides-and-fact-sheets/freshwater-pest-species.
Johnson PN, Brooke PA (1989). Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington. 319pp.
Coffey BT, Clayton JS (1988). New Zealand water plants: a guide to plants found in New Zealand freshwaters. Ruakura Agricultural Cente. 65pp.
Popay et al (2010). An illustrated guide to common weeds of New Zealand, third edition. NZ Plant Protection Society Inc, 416pp. Kasselmann, K. (2003). Aquarium plants. Kreiger Publishing, Florida. 518 pp