Nuphar lutea (L.) Sm., Yellow Water-lily
Account Summary
Native, common and widespread. Eurosiberian boreo-temperate.
1860; Smith, T.O; Lough Eyes.
May to January.
Growth form and preferred habitats
A familiar floating-leaved water-lily of lowland lakes, lakelets and slowly flowing streams and rivers, N. lutea is a perennial with a creeping rhizome. It is usually found in both lake and river water between 0.5-2.5 m deep, over mud and silt bottoms, and it typically bears annually renewed leaves of two kinds: the familiar floating, rounded leathery plates, plus large, crumpled, inconspicuous ones which are translucent and are kept permanently submerged. Possession of these submerged leaves allows N. lutea to dampen the physical effects of water movement, and it tolerates much more mechanical disturbance and associated water turbidity than the related Nymphaea alba (White Water-lily) can manage. However, N. lutea is less tolerant of base-poor sites than the latter and it tends to occur in basic to only moderately acidic waters, seemingly restricted to pH 6.0 and above (Heslop-Harrison 1955a; Preston & Croft 1997). In sheltered, still water sites where the two water-lily species cohabit, which they quite often do, N. lutea typically occupies the deeper, more nutrient-rich water.
The floating leaves of N. lutea are clearly oval rather than circular in outline and the lateral veins divide repeatedly and forking regularly in a herring-bone pattern until they reach the margin, while in cross section the leaf stalks are triangular or semi-circular (ie definitely angular) (Haslam et al. 1975; N.F. Stewart, in: Rich & Jermy 1998).
Again, like Nymphaea alba, N. lutea occurs in both the lowland floating leaf open water plant community and occasionally along the margins of reedswamp, particularly where the water depth shelves steeply, or where there is a faster current beyond. Colonies of Yellow Water-lily can vary enormously in size, from isolated plants in less favourable sites, to situations where it dominates hectares of water at a stretch, spreading both by vegetative growth and branching of the horizontal rhizome, and by seed if water depth, flow and turbidity permits germination and establishment (Heslop-Harrison 1955a; Jonsell et al. 2001).
Flowering reproduction
Individual plants of N. lutea in cultivation are known to survive for at least a century and it is likely that under favourable growing conditions in the wild, plants may persist absolutely indefinitely. In a suitable environment, young plants flower annually and they do so quite freely from their third year of growth onwards. It is not unusual to find a mature plant bearing 15 or more flowers at some stage between early June and late August. The cup-shaped solitary yellow flowers, 4-6 cm across, are borne a few cm above the water surface on very long rigid peduncles. Unlike White Water-lilies, once the flower buds open they do not close again during their 4-8 day flowering period.
The flowers are protogynous (ie female first), the stigmas ripening slightly earlier than the stamens (Velde 1986). Pollination is carried out by a variety of flies, bees and beetles, probably in that order of importance, and there may even be Nuphar specialist pollinating flies (Lippok & Renner 1997). The insects are attracted by a strong flower scent, reminiscent to many humans of plum brandy or a combination of fruit and alcohol. The active ingredient of the perfume is actually ethyl acetate, which is an organic chemical combination of acetic acid and ethyl alcohol (Genders 1971, pp. 27 & 42). The alcohol component is produced in the plant's roots, which appear to tolerate and cope with anaerobic conditions in the muddy bottom exceptionally well. Alcohol is a by-product of the partial breakdown of starch and sugars in the absence of oxygen and, of course, in high concentration it is a lethal toxin that can kill cells. N. lutea transports the alcohol aloft from the submerged roots to the floating leaves and to the flowers, from which it evaporates harmlessly away. Effectively, this is a form of plant excretion, getting rid of a toxic waste-product into the atmosphere (Fitter 1987, p. 218). Consequently, one of the better known English common names of the plant is 'Brandy bottle', although in part this might also be due to the globular shape of the ripe fruit.
The flower visitors are rewarded by a copious and freely available supply of both pollen and nectar foods. The stamens are unusual in that while the anthers are introrse (ie their slit-like openings are directed towards the centre of the flower), as they split to release their pollen they arch over backwards and thus they present their pollen outwards towards the petals. Consequently, automatic self-pollination is avoided and out-breeding is strongly favoured, although an insect walking or staggering around on the flat and relatively broad stigmatic disk, can still occasionally manage to self-fertilise the flower (Heslop-Harrison 1955a).
Fruit and seed production
Again, in further contrast to Nymphaea alba, the fruit develops and ripens just at the water surface, rather than submerged (Velde 1986). The number of seed per fruit is very variable and appears to be under both genetic and environmental control. In cultivation in Sweden, for instance, a mean of 361 seeds per fruit was measured for a sample of 70 fruits, the range of seed production being 45-651 per fruit (Heslop-Harrison 1955a). When ripe, the whole fruit may detach and float around for two or three days before the contained mucilage swells and the fruit bursts or irregularly disintegrates, releasing the ten to 20 fruiting carpels, each containing numerous seeds.
Seed dispersal
In contrast with Nymphaea, seeds of Nuphar do not possess an aril to assist their flotation in water, but the slimy and spongy pericarp tissue which contains small air or gas bubbles serves the same function in N. lutea. Smits et al (1989) concluded that Yellow Water-lily carpels had very poor buoyancy, and that after a day or so (or even less if it rains and releases the air from the bubbles), this spongy mucilage disintegrates and the seeds then immediately sink to the bottom. Since water transport appears to be the most obvious means of dispersal for aquatic macrophytes, the plant propagules of N. lutea appear to be strangely ill-equipped and poorly adapted by evolution for flotation over anything other than short distances. It is known that young seedlings of some aquatic macrophytes also possess powers of flotation and thus a secondary, additional phase of dissemination may occur at a later stage, as is the case with some emergents, eg Baldellia ranunculoides (Lesser Water-plantain) and also some submerged plants, eg Hottonia palustris (Water-violet) (Sculthorpe 1967, p. 329), but as far as we know this possibility has never been observed in N. lutea.
The findings of Mason (1975) with regard to the behaviour of long-established alien aquatic plants in New Zealand underline the poor dispersal abilities of many of them, including N. lutea. Mason showed that although these introduced species were locally abundant, they colonised other isolated water bodies only slowly, if at all, when they were spread deliberately, or accidentally, by man. Without this human intervention they were static and completely confined to existing sites.
Animals that live in, or frequent water, are often considered important dispersal agents, capable of carrying seeds or other transferable vegetative plant parts (Ridley 1930; Sculthorpe 1967). In the case of N. lutea, however, Smits et al. (1989) found no evidence of any adaptation to enable any imaginable form of such animal transport, either attached externally, or ingested and voided in a viable condition through the alimentary canal of fish (Carp), or birds (Mallard duck and Coot). However, viable seeds of N. lutea were once discovered in the excreta of a Heron. The seeds were presumed to have been eaten by a fish, which was subsequently eaten by the bird! Heslop-Harrison (1955a) also quotes the work of a Finnish researcher, who found that seeds removed from the gut of Ridd fish (Scardinius erythrophthalmus), germinated more readily than seeds sown directly from the plant.
More recent work in a sheltered muddy site on the River Rhone in France found that while seed production of N. lutea was at least 600 per m2, not a single seedling of the species was recorded in numerous sample bare mud quadrats examined over an entire five year study period. The only explanation which could be offered was that the muddy sediment in question was very loose and easily re-suspended in water, so that the seeds could sink into the mud to a depth from which seedling emergence simply became impossible. The dynamics of the Nuphar population at this particular site therefore rested entirely upon vegetative extension of the rhizome system (Barrat-Segretain 1996). Water Hens and Grebes might assist in vegetative dispersal, since aquatic birds such as these have been observed carrying uprooted portions of Nuphar rhizome during their nest building (Heslop-Harrison 1955a).
Seed germination
The findings and conclusion of the Rhone work described above is rather surprising in the light of Dutch studies which indicate that germination in this species, while often erratic, is actually better under anaerobic conditions when compared with aerobic, provided the seed has been cold-treatment stratified. The same Dutch study also found that the presence of ethanol and ethylene helped stimulate germination in both Nuphar lutea and Nymphaea alba (Smits et al. 1995). Both seedling and mature N. lutea plants are also known to produce allelopathic compounds, eg resorcinol, plus a number of
alkaloids such as nupharolutine, which appear capable of inhibiting the growth of competing species (Elakovich & Yang 1996; Sutfeld et al. 1996).
Fossil record
The fossil pollen and seed record of N. lutea extends back through all the interglacials to the Pastonian. Both pollen and seed are also frequently recorded in all zones of the current Flandrian interglacial (also known as the Littletonian in Ireland), and pollen appears in low frequency throughout the Late Weichselian glacial stage (the Midlandian in Ireland). Godwin (1975) concludes, therefore, that there is a strong case for regarding the species as persisting in Britain and Ireland right through the Pleistocene, although as one would expect, it must have been restricted during the glacial stages.
Fermanagh occurrence
Nuphar lutea is four times more commonly recorded and at least twice as widespread in Fermanagh as Nymphaea alba (White Water-lily). There are records of N. lutea in 188 Fermanagh tetrads, 35.6% of the total in the VC. Yellow Water-lily is particularly abundant and ubiquitous throughout the whole of the Upper Lough Erne catchment, but is very much less frequent in Lower Lough Erne, where indeed it is absent from most of the shore.
Irish occurrence
In Ireland, N. lutea is much more common and widespread than Nymphaea alba, especially in the Midlands, although like the latter species, it also becomes rare or absent from most of the SE of the island.
British occurrence
Having smaller flowers that are much less decorative than White Water-lily, N. lutea is not nearly so likely to be introduced in English sites and the New Atlas therefore attempts to map the native British distribution. This shows frequent throughout C and S England, but absent from the extreme SE, the Channel Islands, and also from much of the N of Scotland including the northern isles. There appears to be little change in the distribution when it is compared with that in the 1962 Altas (Walters & Perring 1962; Preston et al. 2002).
European and World occurrence
In Europe, it is widespread throughout, extending to 67oN, but thinning markedly southwards in the Iberian and Italian peninsulas, and is scarce throughout the Mediterranean basin, although present and rare in E Algeria (Jalas & Suominen 1989, Map 1514). Eastwards, it stretches through the Middle East, the Caucasus to C Asia, Siberia and Manchuria and there are closely related forms in N America (Heslop-Harrison 1955a; Hultén 1971, Map 158). As with Nymphaea alba, the wide range of N. lutea in Europe and Asia rules out broad regional climatic factors as agents creating the observed uneven British Isles distribution. This must instead reflect the availability of suitable water bodies. The fact that it is more or less a lowland plant again probably reflects its minimum pH (ie pH 6.0), rather than lower temperatures, although higher exposure and more frequent wind on heights might create wave and turbidity problems which would also limit the species (Heslop-Harrison 1955a).
Names
The genus name 'Nuphar' is derived from the Iranian 'nufar' or 'naufar' meaning or referring to a water-lily (Gilbert-Carter 1964). The Latin specific epithet 'lutea' meaning 'yellow' is derived from the name 'Lutum', of the Dyer's Wintergreen or Weld, Reseda luteola, which yields a yellow dye (Gilbert-Carter 1964; Stearn 1992).
Being a common and conspicuous water plant it is not surprising that N. lutea has at least 25 local English common names, of which five are shared with Nymphaea alba (Britten & Holland 1886; Grigson 1987). The name 'Blob' or 'Water-blob', is one of six names shared with Caltha palustris (Marsh-marigold). The word 'blob' or 'bleb' is Anglo-Saxon and means a bladder, bubble or blister (sometimes, as in the Ranunculaceae, indicating the capacity to raise a blister on skin), and the adjective 'blub' refers to something swollen, plump or round, all descriptive terms which could be applied equally well to flowers of Nuphar and Caltha (Prior 1879; Britten & Holland 1886; Watts 2000). Several names suggest the yellow flower in referring to butter and other allusions, for instance 'Butter Churn' and 'Butter Pumps' both refer secondarily to the shape of the fruit. The name 'Golland', 'Water Golland', or in numerous variant dialect spellings as, for example, 'Gowan', 'Gowlan' and 'Gowland', is shared not only with Caltha palustris (Marsh-marigold), but also with Trollius europaeus (Globeflower), the yellow buttercups and, indeed, with almost any yellow flower, or even with one which has a yellow centre, like Bellis perennis (Daisy). 'Golland' is thought to be derived from the Anglo-Saxon 'gold', or if we prefer a remote ancestry, the Suio-gothic 'gul', 'gol', meaning 'yellow' (Britten & Holland 1886). It could also be related or compared to the Norwegian 'gal' or 'gaul', again meaning simply 'yellow' (Grigson 1974). 'Clot' and 'Clote-leaf' are names applied to both N. lutea and Verbascum thapsus (Great Mullein). 'Clote' is Old English and can mean 'wedge', which is probably a reference to the large, broad leaf shape (Watts 2000). Other names and their allusions are discussed under Nymphaea alba, as are the herbal medicinal uses that Nuphar lutea shares with that species.
Threats
None.