Sandersonia aurantiaca Hook., also known as Christmas bells or the Chinese lantern lily, is a monotypic species (related to Gloriosa) which is endemic to southern Africa. The delicate, long-lasting flowers have a vase life of 2 to 3 weeks. The plant is currently enjoying an uprecedented demand worldwide and has potential as a high income earner for fresh cut flower growers. Dahlgren et al. classify Sandersonia in the family Colchicaceae Tribus Iphegenieae. Sandersonia was described by W.I. Hooker in Curtis’ Botanical Magazine in 1853, the plants that were described having been collected by John Sanderson, and thus Hooker named Sandersonia in his honour. The name aurantiaca is from the Latin meaning yellow and scarlet.
The plant grows naturally in an area ranging from the Eastern Cape through Transkei, Natal, Swaziland, into the Transvaal. Flowering time is December to January (Christmas), the lantern-like flowers are borne on the upper part of the stem and open in succession from the lowest flower, the perianth is persistent and protects the ovary. Sandersonia is an erect or scandent geophyte, with a small corm having short spreading lobes and a thin tunic. The stem is simple and supple, with leaves close together, alternate clasping below, the leaf is linear to narrowly ovate-acuminate with a cirrhiferous or aristate tip. Inflorescence cymose, flowers on the upper part of the stem and are placed behind a leaf on long arcuate pedicels. The tepals are fused to form a campanulate perigone. There are six short stamens included, with bilocular anthers introrse and basifixed. The ovary is tri-locular ovoid, obtusely trigonous with many axile ovules, there are three styles and the stigma is apical. Capsules are globose, verrucose with a large broad funicle.
Christmas bells is a popular plant which is now threatened with extinction because of indiscriminate picking and destruction of its habitat for sugarcane fields. The longevity and charm of the flower makes Sandersonia a favourite cut flower. Flower sellers with large bunches for sale were common before Christmas, and, as a result, the habitats were slowly eradicated and the plant is now seldom seen except in protected reserves. Sandersonia is classified as being in danger of extinction in the wild. It has been identified as a potential cut flower due to its charm and good keeping qualities and is currently sold in Japan as bulbs and cut flowers.
Palmer reports that Sandersonia is used by the indigenous populations to procure the birth of a son or daughter as desired, and it has been shown to contain colchicine. Bellet and Gaignault compared the relative colchicine content of the genera Colchicum (the traditional source of colchicine) and Gloriosa. On a dry mass basis Colchicum yielded 0.62% colchicine and 0.39% colchicoside while Gloriosa yielded 0.9 and 0.82%, respectively. Finnie and van Staden compared the colchicine content of Sandersonia and Gloriosa, and found that on a dry mass basis these plants contained 0.8-1.1 and 0.91%) colchicine, respectively making Sandersonia a commercially viable source of colchicine, provided it can be propagated at a fast rate.
Colchicine is an extremely toxic substance which has killed a human adult in a single dose of 3mg. Colchicine is less effective on cold-blooded than on warm-blooded animals. Plant cells are generally less sensitive than animal cells to colchicine, normally plants require 1000 times higher concentrations of the alkaloid to arrest mitosis. Numerous researchers have tried to isolate chemicals with the ability to induce polyploidy, “colchicine is still the only alkaloid that fulfils the different requirements of an effective polyploidising agent”. In the past, the main uses of colchicine were for chromosome manipulation and the treatment of gout. However, at present there is renewed interest in the use of colchicine as a possible cure for cancer-related diseases. Colchicine and related compounds generally exert antimitotic properties, interfere with microtubule-dependent cell function, and irreversibly bind to tubulin. Because colchicine itself is too toxic for human use as an antitumour drug, use has been made of its derivatives which are less toxic. Demecolcine, trimethylcol-chicine acid methyl ester, 2-demethyl and 3-demethylthiocolchicine have been evaluated as anti-leukaemia agents of some promise. Carbamates of colchicine and thiocolchicine are suitable agents for the treatment of gout and murine malignancies.
Colchicine is normally the alkaloid present in the highest concentration in the corm of Colchicum. The meadow saffron or autumn crocus (Colchicum autumnale L.) is the main commercial source of colchicine. Colchicine concentrations vary from organ to organ, and it has been shown that colchicine content may be affected by plant age, season and locality. Finnie and van Staden reviewed the constituents and importance of colchicine in Gloriosa in a previous chapter in this series of books.
Conventional propagation of Sandersonia is via dividing daughter corms or growing from seed. Covered crops generally yield little seed because of lack of natural wind and insect pollination. Brundell and Reyngoud reported on the development and culture of Sandersonia. They found that in soil-grown plants, stem length, number of flowers and daughter corm weight are generally proportional to planted corm weight regardless of corm shape (5 to 10 g being optimal). Shoot emergence is earlier from fork-shaped corms than from marble-shaped corms, and from large corms than from small corms. Harvesting flowering stems at ground level reduces daughter corm yield, while removing immature flower buds increases corm weight slightly as opposed to leaving plants intact. Cutting corms in half hastens the time of emergence of the second stem and increases total daughter corm weight. For container-grown plants, with pre-sprouted corms, shoots emerge after 2 weeks and flowering occurs after 8 weeks, while senescence of shoots commences after about 12 weeks. Corm size continues to increase for 16-17 weeks.
Plants should be grown in well-drained sterile soil with high organic content and a controlled release NPK (15:4:9) fertilizer. Smaller corms should be planted at a density of at least 210/m2 and flowering grade plants at a density of 84/m2. Plants should be watered daily until after flower maturity, grown under 30% shade cloth, and fed every 7 to 10 days with a balanced NPK fertilizer. Corm rot is the major disease. It is caused by Rhizoctonia, Fusarium and Sclerotia species. Corms should be lifted when fully mature, treated with fungicide, and packed dry in sawdust or vermiculite, and stored cool at 4.4 °C for 10 to 12 weeks to break dormancy prior to replanting. Warren reports that there is only one variety and colour; however, in the natural populations in South Africa there are variations in shape.
Most commercial growers purchase small corms from seed growers. “Seed viability is not as big a problem as germination, which can take up to 2 years and is erratic”. There are a variety of seed germination-breaking techniques practised by commercial growers in New Zealand; these include leaving the seeds in porous nets in a cold mountain stream for the winter and letting the ovaries degenerate into a “mush” over winter and planting the resulting mush. Research in our laboratories has shown that using one or a combination of increased oxygen tension, scarification, stratification, endosperm damage or lipid mobilization significantly increases germination. Germination percentages can be as high as 66% within 2 to 3 weeks.
Sandersonia aurantiaca Hook. (Christmas Bells): Summary and Conclusions
Levels of colchicine extracted from callus, malformed roots and entire plantlets respectively, show an increase that can be directly related to the amount of differentiation in culture. Limited plantlet production can be achieved on callus using seedlings as the original explant. Multiple plantlets can be produced using mature corms as explants. Shoots develop from the corm explant and with culture manipulation corm formation can be induced, the resultant corms do not require a hardening off period. It is interesting to note that the response of Sandersonia and Gloriosa in culture is almost identical.
Selections from the book: “Medicinal and Aromatic Plants IX” (1996).