Nelumbo nucifera Gaertn.

Kew Species Profiles

General Description

An aquatic perennial with large showy flowers, the sacred lotus has long been considered a close relative of water lilies. However, lotus flowers differ markedly from those of water lilies, most notably through the obconical (ice-cream cone-shaped) receptacle in the centre, into which numerous free carpels are sunken. Recent molecular research has shown that the closest living relatives of the sacred lotus are the plane trees (Platanus spp., Platanaceae) and members of the protea family (Proteaceae). Their isolated phylogenetic position indicates that both Nelumbo and Platanus may be living fossils (the only survivors of an ancient and formerly much more diverse group).

The sacred lotus has deep religious meaning to Hindus and Buddhists, to whom the lotus flower symbolises beauty, purity and divinity. In Hinduism the sacred lotus represents the sun, and is associated with mother goddesses as a symbol of fertility. 

Nelumbo nucifera has been in cultivation in China for more than 3,000 years, and has been grown not only for its cultural and ornamental value, but also for medicinal uses and for its edible 'seeds' and rhizomes. In China, Japan and India, for example, the rhizomes are roasted, pickled, candied or sliced and fried as chips. A paste made from the nutlets is used as a filling in 'mooncakes', traditional Chinese pastries.

The young leaves, leaf stalks and flowers are eaten as vegetables in India.

Species Profile

Geography and distibution

In the wild, the sacred lotus occurs in warm-temperate to tropical regions of Asia (Iran to China, Japan and New Guinea) and northeast Australia.

Description

The sacred lotus is a perennial aquatic plant with rhizomes (often mistakenly called 'roots') that grow in the mud at the bottom of shallow ponds, lakes, lagoons, marshes and flooded fields. Its large, peltate (with the leaf-stalk attaching to the centre, rather than the edge) leaves rise above the water surface on 1 to 2 m long petioles. The strikingly water-repellent leaf surface has inspired the term 'lotus effect'. This term describes the leaves' self-cleaning capacity which is a result of dirt particles being picked up by water droplets due to a complex nanostructure of the leaf surface, which minimises adhesion.

Threats and conservation

Although abundant in cultivation, with many different cultivars having been bred over the centuries, local wild populations of sacred lotus in central mainland China have been greatly reduced due to the rapid development of the aquaculture industry.

Kew's Millennium Seed Bank: seed storage

Kew's Millennium Seed Bank Partnership aims to save plant life world wide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.

Number of seed collections stored in the Millennium Seed Bank: None. Two collections of the related species Nelumbo lutea are held, both of which are from the Lady Bird Johnson Wildflower Centre, Austin, Texas

Seed storage behaviour: Orthodox (the seeds of this plant survive being dried without significantly reducing their viability, and are therefore amenable to long-term frozen storage such as at the MSB)

Long life seeds

Lotus 'seeds', which are botanically nutlets of a multiple fruit with a very hard air-and water-impervious pericarp, have long been claimed to live for centuries. Scientific proof of their fabled longevity was only provided in 1995 by Jane Shen-Miller.

The University of California research biologist was able to germinate lotus seeds recovered from a dry lakebed in the former Manchuria (now part of northeastern China). Modern accelerator mass spectroscopy techniques allowed precise radiocarbon-dating of a minute piece of the thick and hard pericarp of the nutlets without killing the seeds. With this method, the age of the oldest germinating seed was determined to be 1,288 (plus or minus 250) years!

Cultivation

The sacred lotus can be propagated from seed. The long-lived seeds have extremely hard coats, one end of which must be filed away to expose the endosperm before germination. The seedling will then begin to emerge 24 hours later when placed at 25-30˚C. The seedlings require high light levels in order to form a tuber that is large enough to survive its first winter.

Propagation can also be carried out by division in late winter, just before the growing season. At Kew, this difficult task is carried out during re-potting, when the plants are dormant. After a growing season it can be possible to find several tubers in a large pot. The growing tips must not be damaged, so the compost should be washed away carefully and the growing tips located. The material for propagation should consist of a growing tip, behind which there is a constricted area, followed by a tuber and another constricted area followed by a tuber and finally another constricted area with a tuber behind, through which the cut can be made. This material, looking like two and a half sausages, can be placed in an individual pot.

The propagation material should be covered with at least 10 cm of soil (loam), and placed in a position that will avoid damage to the growing tip from contact with the pot side. A gap of at least 15 cm should be left above the soil at the top of the pot. This gap allows space for a reservoir of water if the pot is taken out of the pond, and prevents the rhizome from coming out of the pot when the pot is in a pond.

Both division and seed sowing have successfully produced new sacred lotus plants at Kew. The mature plants are kept in round 50-litre pots, without any drainage holes, because drainage holes or the corners of square pots could trap the growing tips. It is possible to move these watertight pots between Kew's display houses and the Tropical Nursery for overwintering. The plants are kept under water at all times, at a depth of 10-30 cm.

Fine grade loam is used at Kew for potting, because it is high in nutrients, does not float when immersed and locks in the 'food-balls' that are used during growth periods. These food-balls are made at Kew using organic fertiliser mixed with wet loam and rolled into lozenges. The lozenges are inserted into the loam in the pot. Care has to be taken when doing this to avoid damage to growing tips.

In the UK, low light levels in winter cause the sacred lotus to have a period of dormancy. At this time the tubers can be stored in damp mud in frost-free conditions. Hardiness is variable; however, to achieve fast growth and free-flowering, a minimum temperature of 25˚C would be required for most plants during growth periods.

At Kew the sacred lotus can be prone to attack from mealy bug, spider mite and aphids. It is difficult to treat any problems with chemicals as the leaves are sensitive to pesticides, alcohol, white oil, plant invigorators and soap. However, cultural controls are adopted as much as possible.

The sacred lotus at Kew

Twenty specimens of Nelumbo nucifera are held in the Economic Botany Collection, one of the behind-the-scenes areas of Kew, made available to bona fide researchers from around the world by appointment. The items include flowers, fruits, seeds, starch from rhizomes and flour from the nutlets. One of the items in the collection is a necklace made from the nutlets of sacred lotus, seen in the image, left.

The Herbarium, another behind-the-scenes areas of Kew, contains two alcohol-preserved specimens of Nelumbo nucifera . The details of these specimens can be viewed in the Herbarium Catalogue, and the specimens themselves are made available to researchers by appointment.

Development and evolution of pollen at Kew

Recent work has included the study of aperture variation in the pollen of Nelumbo . Apertures are important features of pollen. They are gaps in the tough pollen wall, through which exchange of solutions and chemical information can take place, and through which pollen tubes germinate. Their shape, size and relative position have changed during the course of evolution, from one aperture placed at the end of the grain (known as monosulcate) to three evenly distributed around the middle (known as triaperturate or tricolpate) (Figure 1).

Why has this happened?

How or why this has happened is not yet fully understood, however approximately three quarters of all angiosperm (flowering plant) species belong to the eudicot clade, which is united morphologically by a single synapomorphy (shared derived trait) —triaperturate pollen. It therefore appears that pollen based on the triaperturate pattern is an important and successful advancement that could represent a key innovation underlying eudicot success.

Molecular data suggests that  Nelumbo  is one of the first-branching members of the eudicot clade. Kew research has examined evidence that tricolpate and monosulcate pollen types are produced alongside each other in the anthers of  Nelumbo  flowers, as had previously been reported. Kew studies found only evidence of tricolpate pollen types and the associated type of development, although some aberrant pollen grains were found.

Distribution

China, Japan

Ecology

Warm-temperate to tropical climates, in a range of shallow (up to about 2.5 m deep) wetland habitats, including floodplains, ponds, lakes, pools, lagoons, marshes, swamps and the backwaters of reservoirs.

Conservation

Not yet evaluated against IUCN criteria.

Hazards

None known, although Nelumbo nucifera contains some alkaloids, such as nuciferine, aporphine and armepavine.