Mexican waterlily or Banana waterlily [Nymphaea mexicana Zucc.][NYMME][CDFA list: B] Photographs Map of Distribution

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SYNONYMS:banana waterlily, yellow waterlily, Castalia flava (Leit.) Greene

GENERAL DESCRIPTION:Noxious aquatic perennial with creeping stolons, floating leaves, and showy yellow flowers. Plants can rapidly colonize shallow waters. Heavy infestations in slow moving channels, lakes, reservoirs, and ponds can restrict water movement, contribute to siltation, increase evapotranspiration rates, and hinder recreation activities. Introduced from Southeastern U.S. and Mexico as an aquatic ornamental.

SEEDLINGS:New plants develop from stolons before seedlings mature.Early leaves submerged. Cotyledons remain within seed coat. First leaf linear. Subsequent leaves narrowly arrowhead-shaped, ~ 2-5 cm long. First floating leaves resemble ~ 2-3 cm long mature leaves.

MATURE PLANT:Leaves floating to emergent when crowded, nearly round, flat to cupped, narrowly cleft at the base with edges often overlapping, 10-25 cm wide. Upper surfaces glabrous, glossy bright green, often brown blotched. Lower surfaces often deep red to purplish-brown and black-spotted. Leaves usually die during winter. New spring leaves are submerged, narrowly arrowhead-shaped, ~ 2-7 cm long.

ROOTS and UNDERGROUND STRUCTURES:Dormant in the cool season. Tubers vertical, 2-30 cm long, 1.5-6 cm in diameter, covered with long light-colored hairs and persistent wart-like petiole bases, anchored by many fibrous roots. Stolons creeping, white, ~ 1 cm in diameter, grow from the upper portions of tubers. Stolon tips have a few shoot buds and a cluster of banana-shaped storage roots 2-3 cm long that overwinter buried in 20 cm or more of mud. In spring, shoot buds elongate into stolons that produce new plants. Tubers seldom survive drying conditions.

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FLOWERS:Spring-fall. Flowers musty-scented, bright yellow, 6-12 cm in diameter, typically emergent to ~ 10 cm above the water surface. Sepals 4, lanceolate to elliptic. Numerous petals gradate into numerous smaller, petal-like stamens. Ovary partially inferior, with curved finger-shaped stigmas. Flowers open near noon and close late afternoon for 2 consecutive days. Stigmas are receptive to insect pollination the first day. Anthers shed pollen the second day. Closed flowers submerge to develop fruits.

FRUITS and SEEDS:Berries submerged, green, ovoid, ~ 2.5 cm long, burst to release 4-60 seeds with buoyant arils. Seed spherical, ~ 0.5 cm in diameter, dull greenish-black, covered with fine hairs.

POSTSENESCENCE CHARACTERISTICS:Mature leaves decay rapidly during the cool season.

HABITAT:Still or slow moving shallow waters in lakes, ponds, streams, canals, and ditches.

DISTRIBUTION:Uncommon. San Joaquin Valley. To 100 m (330 ft).

PROPAGATION/PHENOLOGY:Reproduces vegetatively from stolons and by seed. New plants arise ~15-60 cm from the parent plant by horizontal stolons. Seed disperses by floating. Seed does not survive drying and must be submerged to germinate. Most germination occurs at 19-23º C.

SIMILAR SPECIES:Fragrant waterlily [Nymphaea odorata Aiton.][NYMOR] is also a noxious aquatic perennial of quiet shallow waters. Unlike Mexican waterlily, fragrant waterlily has sweet-scented white flowers and long, branched, creeping rhizomes 2-3 cm in diameter that are densely covered with short black hairs. Fragrant waterlily grows in acidic to alkaline waters and has rhizomes that can tolerate some desiccation. Seed germination in fragrant waterlily requires light and the presence of ethylene, a gas whose production is stimulated when seeds are crowded together. Germination is enhanced by cold stratification for several months. This species is widely dispersed and expected to expand range. Sierra Nevada, especially Lake Tahoe, Sacramento Valley (especially Butte Co.), San Bernardino Mountains. To 2700 m (8850 ft). Introduced from the Eastern U.S.


Prevention and control: Yellow water lily was previously introduced to California from Florida and Mexico for ornamental purposes. It may infest lakes, ponds, or slow moving waterways and rapidly spreads in shallow waters. Once established, yellow water lily is very difficult to eradicate. Yellow water lily reproduces vegetatively by stolons and tubers which are difficult to remove. Topgrowth can be cut and removed repeatedly to reduce populations. However, regrowth will rapidly occur. Herbicide options include glyphosate and fluridone. Consult the herbicide label for proper rate and timing. Treatment of entire ponds should be done in sections to prevent low oxygen levels due to decomposing plant material following herbicide application. There is little information available for control of this species.

Krake, K. 1999. Emerging aquatic weeds. Plant Protection Quarterly 14 (2):79.

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