Nymphaea nouchali var. caerulea, or simply Nymphaea caerulea, also known as blue lotus or blue water lily among many other names, is a water lily in the genus Nymphaea, a botanical variety of Nymphaea nouchali.
It is an aquatic plant of freshwater lakes, pools and rivers, naturally found throughout most of the eastern half of Africa, as well as parts of southern Arabia, but has also been spread to other regions as an ornamental plant. It can tolerate the roots being in anoxic mud in nutritionally poor conditions, and can become a dominant plant in deeper water in such habitats. The underwater rhizomes are edible.
It features prominently in Egyptian mythology and art, symbolizing the sun and rebirth and has been found in pharaohs' tombs. It may have been used for aphrodisiac and religious purposes, including in rituals like Hathor's Festival of Drunkenness. The plant contains the psychoactive alkaloids nuciferine and apomorphine, which interact with the serotonin, dopamine, and adrenergic systems. Modern recreational use, primarily through drinking infusions or vaping, has been associated with toxicity, causing symptoms like sedation and perceptual disturbances. Recent research by UC Berkeley confirmed that the authentic Nymphaea caerulea is chemically distinct from many products sold online, which contain significantly less of the alkaloid nuciferine and are misidentified water lilies.
Nymphaea caerulea, first described by Marie Jules César Savigny in 1798, was later classified as a variety of Nymphaea nouchali by Bernard Verdcourt in 1989. Though it is still most commonly referred to as a variety of Nymphaea nouchali, recent phylogenetic studies have problematized the taxonomy. When defined taxonomically as Nymphaea nouchali var. caerulea, it is considered synonymous with Nymphaea capensis. When considered taxonomically as Nymphaea caerulea, it is now rare due to habitat loss from the Aswan Dam.
Description Vegetative characteristics
This is an aquatic (euhydrophyte) herb with a tuberous rhizome. That is to say, it has small tubers that may develop into short vertical rhizomes. It is a perennial. One plant can spread over an area of about 1 metre.
The peltate leaves have long petioles and have leaf blades (lamina) which are by in size. The leaves are polymorphic, changing in form and texture depending if they are underwater or floating. These laminae have a chartaceous texture and can be glabrous or densely covered in pubescent hairs. The shape is incised-cordate and orbicular or subelliptic, with an acute or caudate apex. The two lobes can overlap somewhat or be slightly apart from each other. The upper surface of the lamina is smooth, but the underside has conspicuously raised, green or rarely reddish or reddish-purple veins. There are eight to eleven primary lateral veins on each side of the midrib. There are six to eight pairs of secondary veins arising from the midrib. The primary veins form a pattern of closed, elongated areas stretching to more than two thirds of the way to the margin of the leaf. The leaf margin is entire towards the apex or more-or-less irregularly sinuate-lobulate throughout its entirety. The petioles are thick, blackish green and spongy. They continue to lengthen as they age, pushing older leaves towards the margins of the plant.
Generative characteristics The flowers can be blue, white, mauve or pinkish in colour, but usually have pale bluish-white to sky-blue or mauve petals, smoothly changing to a pale yellow in the centre of the flower, and are in diameter. There are four sepals; these are coloured green and sometimes purple at the margins, and are by in size. There are 14–20 petals, of which the outermost are as long as the sepals. Their shape is oblong, and their apexes end in blunt or subacute tips. The stamens are densely congested and very numerous, numbering 100–200 or more. The outermost stamens have long appendages. There are 14–24 carpels, with a very short style. There are also carpellary appendages; these are what is known as 'osmophores', structures which serve to attract pollinators without actually rewarding them, thus by deceit. In this case they are visually attractive for bees and exude an odour mimicking food.
The flower buds rise to the surface over a period of two to three days, and when ready, open during the mid-morning, closing near dusk. This ability is controlled by the sepals; when these are cut off, the flower loses the ability to close. The flowers and buds do not rise above the water in the morning, nor do they submerge at night. The flowers last some four days before they start to wither, closing up each night.
The fruit are berries, 2.2 by 3.2 cm and flattened-round in shape. The seeds are ellipsoid and 1.2 mm long. They are smooth, and have a fleshy, bell-shaped aril.
Chemical composition The plant's psychoactive properties are primarily attributed to the aporphine alkaloids nuciferine and apomorphine:
Nuciferine has a more complex receptor binding profile, acting as an antagonist at the serotonin 5-HT2A receptor, a partial agonist at the dopamine D2 and D5 receptors and serotonin 5-HT6 receptor receptor, and an inhibitor of the dopamine transporter or dopamine reuptake inhibitor. Its degradation product, atherosperminine, is also associated with dopamine receptor agonism. Apomorphine acts as a non-selective dopamine receptor agonist and serotonin receptor modulator, with partial agonist activity at the serotonin 5-HT1A receptor and antagonist activity at the serotonin 5-HT2A receptor. It's also an α-adrenergic receptor antagonist or alpha blocker. The drug's potential use in treating erectile dysfunction may explain the plant's historical reputation as an aphrodisiac;
Analyses of commercial products show inconsistent alkaloid content. A study found nuciferine in all tested "blue lotus" products, but apomorphine in only a few.
Nymphaea caerulea contains the psychoactive alkaloid nuciferine, which contributes to its euphoric effects. Chemical analyses using mass spectrometry have shown that authentic flowers have significantly higher concentrations of nuciferine compared to other water lilies.
Historically, research into the plant's chemistry produced different findings. In the 1970s and 1980s William Emboden suggested that Nymphaea caerulea contained aporphine alkaloids (though photochemical studies were not performed); however at the time aporphine alkaloids were not found in the photochemical studies performed, and the chemical composition of Nymphaea caerulea was discovered to include compounds such as 7-hydroxyflavone, 4,7-dihydroxyaurone, and 4'-hydroxyaurone, along with methyl vanillate and cinnamyl alcohol.Yoshpa, M. (2004). Ethnobotany and Phytochemistry of the Sacred Blue Lily of the Nile, Nymphaea caerulea Savigny, Nymphaeaceae (PhD Thesis).
Cytology The chromosome count is n = 14. The genome size is 567.24 Mb.
Taxonomy Nymphaea spectabilis, a purple form known from cultivation, and N. capensis, found throughout eastern, central and southern Africa, as well as a number of other named taxa, were synonymised to N. nouchali var. caerulea in the 1989 addition to the Flora of Tropical East Africa (FTEA) series, a position which has generally been accepted, although some of the authorities in Bangladesh and in the United States disagree.
In 2012 there was a phylogenetic study where N. caerulea was more related to N. gracilis, an endemic of northern Mexico, than it was to N. nouchali. The evolutionary tree was a consensus of ITS2 and matk. According to this study, N. caerulea should not be considered as a variety of N. nouchali. When genomes from the water lily genus (Nymphaea) were published in the journal Nature in 2020, N. caerulea was cited under that name, not as N. nouchali var. caerulea. Another phylogenetic study from 2021 found N. caerulea (as N. capensis) to be closest related to N. colorata, an east African species.
Nymphaea nouchali is itself a taxonomically challenging species, with a distribution that spans Australia, throughout southern Asia, across Africa to the Western Cape. It has many colour forms (with red-coloured forms generally called N. stellata) and has a long history of cultivation. In Africa, following the 1989 FTEA publication, five different varieties are recognised: var. caerulea, the most widespread, ovalifolia, in parts of tropical Southern Africa, petersiana, the same, zanzibarensis, from tropical southern, central and East Africa, and mutandaensis, which is an endemic of Uganda. One of these taxa, var. petersiana, was found to be quite divergent in the 2012 study. If the 2012 study is to be accepted, this may indicate that the African populations of N. nouchali belong to another species than the Asian and Australian type populations, and should likely be renamed N. caerulea as this name has priority over N. capensis.
Publication It was first described as Nymphaea caerulea Savigny by Marie Jules César Savigny in 1798. Later, it was included in the species Nymphaea nouchali Burm.f. as the variety Nymphaea nouchali var. caerulea (Savigny) Verdc. published by Bernard Verdcourt in 1989.
Classification It is classified in the Nymphaea subgenus Brachyceras. This subgenus appears to be phylogenetically sound.
Distribution The native distribution covers North Africa along the Nile and south throughout central, East and Southern Africa. It is common in this range. The conservation status has not been evaluated by the IUCN, but it is considered a species of 'least concern' by the South African National Biodiversity Institute in their Red List of South African Plants.
On the African continent, it occurs, from north to south, westwards to at least Chad, Congo-Brazzaville, the DRC (only in Katanga?), Angola and Namibia. In South Africa this plant is found in every province, as well as in eSwatini, but it is not native to Lesotho and the Western Cape. It also occurs on islands off the eastern African coast: Zanzibar, Madagascar and the Comoro Islands. It is native to Yemen and Oman (in Dhofar) in the southern Arabian Peninsula but, according to Moshe Agami in a 1980 paper, is thought to have become extinct in the wild in Israel.
It has more recently been spread more widely around the world as an ornamental plant, and introduced populations are now found in Bangladesh, Meghalaya, Kerala and Assam in India, Fiji, Mauritius, North Island in New Zealand, New South Wales and Queensland in Australia, Cook Islands, Costa Rica, and throughout eastern South America (in Brazil and Argentina).
There is an introduced population of blue water-lilies originally from East Africa in the US in the state of Florida. This was first identified as N. zanzibarensis, then as N. capensis var. zanzibarensis, but following the 1989 FTEA publication the taxon was moved to N. nouchali var. zanzibarensis. Nonetheless the 1997 addition to the Flora of North America series decided to retain recognition of the local population under the name N. capensis, and this population continues to be recognised under that name in the US.
The naturalised populations in eastern Australia were also thought to be N. capensis var. zanzibarensis, then later N. caerulea var. zanzibarensis, then in 2011 N. capensis, but the plants in the wild are now thought to be N. caerulea. It is considered an environmental weed in Australia.
Ecology It has a habitat consisting of rivers, lakes and pools. As of 1921, it has been found at elevations of in South Africa.