Botany of Blue lorus  (Nympaea caerulea)

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Nymphaea nouchali var. caerulea (Sav.)
Family: Nymphaeaceae (Water Lily Family)
Common Names: Blue Water Lily, Frog’s Pulpit, Blou Plomb, iZubu(Z) and Blue Lotus in Egypt


This lovely aquatic plant with sky-blue flowers is South Africa’s most commonly grown indigenous water lily.

It is a clump forming perennial with thick, black, spongy, tuberous rhizomes anchored in the pond mud by spreading roots. The water lily does not have true stems, the leaves are on long petioles (leaf stalks) that arise directly from the rhizome. The leaves are large and flat, rounded or oval in shape with notched margins, up to 40 cm in diameter, and cleft almost to the centre where the petiole is attached. They are relatively short lived and are replaced regularly throughout the growing season. They start out as a soft shiny green at the centre of the plant. As they age, the petiole lengthens, pushing the leaf towards the outer perimeter making room for the new growth, and they develop light brown or purple splashes which eventually cover the leaf, leaving only the veins green. They then start to die, turning yellow then brown and eventually disappearing under the water. One plant can spread over an area of about 1 m..

The leaves show many interesting adaptations to their watery environment. The margins are slightly rolled inwards toward the uppermost side (involute) which helps keep the blades afloat. The underside of the leaf, which is continually wet, has a strong attraction to the water and this holds the leaf flat against the water. The veins act like a structural support for the leaves. The upper leaf surface is coated with a smooth waxy cuticle, which gives it the appearance of being leathery and shiny. This water-repellent waxy layer is of vital importance to the plant, not only to help prevent the leaf from sinking, but also to prevent the tiny stomatal pores, through which it breathes, from becoming clogged with dust. When water splashes onto the leaf surface, it forms rounded droplets that roll across the surface cleaning up the dust as they go. Clean dust free leaves are also better able to photosynthesise effectively.

Another problem facing aquatic plants is the supply of oxygen to their roots. Roots must constantly be supplied with oxygen to stay healthy and the water lily’s roots are buried in poorly aerated pond mud and therefore cannot get oxygen they way normal plants do. It has overcome this difficulty by developing a system of large internal ducts throughout the leaves, petioles and roots which ferries the oxygen from the leaves to the roots.

The large, elegant blue flowers are held well above the water at the tip of a sturdy green stalk and appear almost constantly from spring until the end of summer (September to February). They are bisexual, star-like and regular (actinomorphic), with 4 sepals, green on the outside and white to blue on the inside, and many blue petals. In the centre of the flower are numerous blue-tipped bright golden yellow stamens. There are colour forms other than blue that occasionally occur, e.g. white, mauve and pink, but blue is the most common and the water lilies at Kirstenbosch are blue. The flowers open in early to mid-morning and close completely in late afternoon and stay closed all night. The opening and closing mechanism of the flowers is controlled by the sepals. If they are removed, the flower loses the ability to close. A fully open flower measures 15-20 cm across and each flower lasts for about four days. The flowers are sweetly fragrant and are visited constantly by bees who are the most likely pollinator.

The famous night-flowering giant water lily of the Amazon, Victoria amazonica has a complicated pollination mechanism where beetles are trapped inside the closed flower where they are given a meal in exchange for getting covered by pollen. When they are released, laden with pollen they head straight for the newly opened fresh flowers of neighbouring plants. It does not appear that the nymphaeas employ such a complicated strategy. The spent, pollinated flower closes completely, looking like a bud, enclosed once again by the sepals. It sinks underwater where the ovary develops into a hard green berry-like ovate to pear-shaped fruit. In clean water they can be clearly seen resting on the pond floor. When mature, the walls decay to release thousands of small (1.2 x 0.8 mm) ellipsoidal seeds, each surrounded by a membranous aril which causes them to float for a while, allowing the seeds to disperse from the parent plant, before it disintegrates and they sink under the water onto the mud.

The Water lily Family

The water lily family, Nymphaeaceae, is an old and evolutionarily primitive one, and is grouped with buttercups (Ranunculus) and magnolias in the order Ranales. Furthermore, fossil evidence suggests that nymphaeas have not changed much over the past 160 million years. All they have done is move about the globe, keeping in the tropical and temperate zones. Another well known genus in this family is Victoria, the giant amazon water lily.

The genus Nymphaea consists of roughly 40 species found in tropical and temperate climates of both hemispheres. It is full of synonymy, because different populations or colour forms have been described as separate species which have since been sunk into one species and in some cases the same plants have been described as different species by different botanists, or the name of one species has been misapplied to another species. It all gets rather confusing. There are also many variants and hundreds of hybrids that come in all colours, shapes and sizes.

There are only two species that occur in southern Africa. One is Nymphaea lotus, the white water lily, or white lotus which has night-blooming white or cream flowers and is widespread in tropical Africa to southern Africa, where it occurs in the former Transvaal, KwaZulu-Natal, Botswana, Swaziland and Namibia, and in Madagascar, in sheltered water 0.5-2.5m deep and in swamps. It also occurs in hot springs in Hungary and Romania. There is a variety in Australia and it is widely cultivated in the USA and South America

The other southern African species isNymphaea nouchali. The blue lotus, Nymphaea caerulea and the Cape blue water lily, Nymphaea capensis are no longer regarded as distinct species and have been sunk into this genus. The type specimen was collected in Coromandel in India. The meaning of the specific ephithet nouchali has only been traced with the assistance of staff at Kew who report that one of their specimens contains a note that Noakhali is a district in Bangladesh. The variety name caerulea refers to the sky blue colour of the flowers.

In Africa, this species occurs in tropical to southern Africa where it is common, although not as common as it used to be, in pools, dams, vleis and swamps, seasonal ponds, lake-edges and slow-flowing streams and rivers, mostly in water 30 to 90 cm deep. There are five African varieties:
Nymphaea nouchali var. caerulea which is widespread all over South Africa, Swaziland, Botswana and Namibia as well as further north in Zimbabwe, Zambia, Malawi, Angola, Mozambique, DRC, Uganda, Kenya, Tanzania Sudan, Egypt and west Africa, from sea level to 2700 m. In the Western Cape it is often found growing with Aponogeton distachyos, the waterblommetjie.
Nymphaea nouchali var. ovalifolia, which occurs in the former Transvaal and Botswana, as well as in Tanzania and the DRC.
Nymphaea nouchali var. petersiana which occurs in the former Transvaal, KwaZulu-Natal and Namibia, and in Tanzania, Mozambique, Malawi, Zimbabwe and Angola.
Nymphaea nouchali var. zanzibarensis which occurs in the former Transvaal and KwaZulu-Natal, and in Mozambique, Kenya, Tanzania and the DRC.
and the last one Nymphaea nouchali var. mutandaensis which occurs only in Uganda.


History and legends

Water lilies, particularly nymphaeas, the true water lilies, are steeped in history and tradition. The name of the genus Nymphaea is a direct transliteration of a Greek word which Theophrastus (a disciple of Plato and Aristotle) used to describe these plants about 300 years before the common era, and refers to the practice of early Greeks in dedicating the water lily to the semi-divine water maidens, the nymphs. This is however by no means the earliest record that we have of the water lily. In Egypt, Nymphaea caerulea (now sunk in Nymphaea nouchali var. caerulea), the blue lotus and Nymphaea lotus, the white lotus, have been admired, painted, eaten, grown and revered for thousands of years. The goddess Isis is said to have pointed out that the rhizomes were edible, and its flowers, buds and leaves are often depicted on ancient monuments, in murals, on pottery and on furniture. Monarchs and priests of ancient Egypt were laid to rest with wreaths made from the petals of the blue lotus, laid in concentric semi-circles from the chin downwards. There is also evidence, in the form of a painting in a tomb dating back to 3000-2500 BCE, that nymphaeas were deliberately cultivated in square, evenly spaced beds fed by canals. The blooms were in great demand for religious festivals, offerings of the flowers being made to the dead or to the gods, as well as for gifts to visiting noblemen as a gesture of friendship and goodwill. And later on, both Amenhotep IV and Ramses III (1225 BCE) are known to have had them growing purely for their ornamental value in their palace gardens. The reason for their veneration lies in the belief that the beautiful blooms of the water lily, rising pure and clean from the slimy mud, were comparable with the aspirations of mankind: purity and immortality.

In China water lilies are thought to have been grown for many years. There is a beautiful passage by Chou Tun-I of the eleventh century T’ang Dynasty: ” . . my favourite is the water lily. How stainless it rises form its slimy bed. How modestly it reposes on the clear pool, an emblem of purity and truth. Symmetrically perfect, its subtle perfume is wafted far and wide; while there it rests in spotless state, something to be regarded reverently from a distance, and not to be profaned by familiar approach.”. It has also long been cultivated by the Japanese.

In modern times, the name lotus is used almost exclusively for Nelumbo nucifera, also called the sacred lotus or incorrectly the Egyptian lotus. Nelumbo nucifera is not a native of Egypt. It actually comes from south-east Asia where it is often found near temples and is regarded as sacred in China and Japan. It was introduced to the Nile by the Romans, probably for food. The true Egyptian lotus is Nymphaea nouchali var. caerulea (syn. N. caerulea) and Nymphaea lotus.

Back home, in earlier times (c. 1800) in South Africa, the rootstock of the blue water lily was collected and eaten, either raw or in curries, in particular by the Cape Malays and farming communities in the Cape. Today, only waterblommetjies, Aponogeton distachyos, are still eaten.

The common name kaaimanblom, which means merman’s flower in English, was acquired because this water lily is often found growing in a deep pool (kaaimansgat), and popular superstition had it that a merman (kaaiman) dwelt in such a pool and would drown anyone swimming in his pool. Furthermore, it was suspected that the merman put the flowers there specifically to attract his victims, especially disobedient boys. It gets the name frog’s pulpit / paddapreekstoel, because the leaves provide resting places for frogs.

Growing Nymphaea nouchali var. caerulea

Water lilies are simple to grow, all they need is full sun, some good soil and at least 30 cm of still water. Full sun is necessary for the plants to grow vigorously and produce flowers as well as for the flowers to open during the day. They do not like to be in a pond with a fountain or in swiftly moving water, neither do they like wind.

Two planting methods are commonly used for water lilies. Either the pond floor can be covered with about 15cm of a sand and compost mixture and the plants grown directly in this, or else they can be planted in a container which is sunk into the pond. The latter method is often preferred as the plants are more easily removed for inspection or division, or for the pond to be cleaned. Specially manufactured plastic water lily baskets are the most suitable and are available from most garden centres. As they have latticework sides, it is advisable to line them with hessian before planting to prevent soil spillage into the water.

Water lilies are heavy feeders. In a natural pond the accumulation of humus at the bottom is sufficient to maintain lush growth. In artificial ponds and particularly for container grown plants, it is important to add sufficient nutrients to the soil. If not the plant will soon use up all available nutrients and stop thriving. Just about every water lily enthusiast will have his or her preferred soil mixture. Good sieved garden loam is a recommended base although some swear by pure unwashed river sand. It can be mixed with artificial fertiliser, or two parts loam can be mixed with 1 part well rotted cow manure or equal parts loam, compost and well-rotted cow manure can be used. If using cow manure and compost it is important that it not be allowed to come into direct contact with the water. Coarse ground hoof and horn or bonemeal can also be mixed in. However, it is a delicate balance because if too much nitrogen rich material or fertiliser is used, it can cause an algae bloom in the pond which will leave your fish swimming in pea-soupy water. Also, it may encourage your water lilies to over exuberant growth. If you are too stingy with fertiliser and the potted water lilies fail to thrive, a slow release fertiliser pill can be pushed into the soil near the roots.

The crowns of the lily (the part of the plant where the leaves all originate from) should be planted firmly just protruding above the surface of the soil and the soil should be covered with a layer of river sand and pebbles in order to keep the water clean. The container should be drenched, and then placed a few centimetres below the surface of the water or to where its leaves float naturally (i.e. to the level it was in the Garden Centre). If your pond is deeper, the plant will adjust as the petioles respond quite quickly to relatively small changes in depth. Nymphaea nouchali var. caerulea requires about 30 cm, but no more than 90 cm. of water above its crown.

An easy way to get loose, uprooted full grown plants established in a natural or soil-filled pond is to tie a weight around the base of the stem and then toss it into the pond where you would like the new plant to grow. Make sure that the depth is adequate, and the leaves will find their own level and within a few weeks the roots will have grown into the mud/sand at the bottom of your pond. A new plant can also be bagged with soil in a hessian square, the four corners tied into a package which is lowered into a natural or soil-filled pond. The hessian will eventually rot by which time the plant will be established on the pond floor.

Nymphaea nouchali var. caerulea grows easily in any part of southern Africa, including the highveld and can be considered hardy to a winter minimum of -1 to 4 oC / 30 to 40 oF (Zone 10). In climates colder than this they will most likely be killed if left outdoors during winter. Although the blue water lily does go dormant during the winter, it should be left in the water throughout its dormancy. At the coast they keep their leaves during winter.

Water lilies are without doubt the most beautiful aquatic plants and are a must for every sunny water garden. But they need not only be used in ponds. Innovative gardeners with small gardens and sunny courtyards can enjoy them too, as they can be successfully grown in a variety of water-filled pottery containers, wooden barrels, old kitchen sinks and water features.

Propagating Nymphaea nouchali var. caerulea

The easiest method of propagation is division. Plants may be left in place for two years, but pot grown plants are best lifted, divided and planted in fresh soil each year for good results. The plants are best lifted and divided just before new growth commences in the spring (August). Pull or cut the fleshy roots (rhizomes) apart and replant immediately in fresh soil mixture. Each new plant should have at least one bud at the tip of the rhizome.

The blue water lily may be grown from seed, but this requires patience, for the plants take 3 to 4 years to flower. It is difficult to collect the seed, because the seed pods burst without much warning and the seeds disperse and sink quite soon. A common practice is to tie a muslin bag around the ripening pod. In this way after it bursts, the seeds cannot float away. The seed can be sown in spring and during summer (September-January). Finely sieved clean loam soil without any organic matter or fertiliser is best. Seed should be sown thinly, covered lightly with soil and then plunged into shallow water, no deeper than 2.5 cm, and placed in a sunny position. Germination should take 3-4 weeks The seedlings will look like fine grass at first, developing true leaves later. When the first two or three floating leaves appear the seedling should be pricked out and planted into individual containers and immersed back in the water. They may be submerged into deeper water and larger containers as they grow and lengthen.


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Verdcourt, B., 1989, Flora of Tropical East Africa, Nymphaeaceae 3-11
Author: Cherise Viljoen and Alice Notten
Kirstenbosch National Botanical Garden
January 2002.