The Genus Cymbidium

What is Cymbidium Leaf Anatomy Seed Structure Cytology Cymbidium in Cultivation New Classification
Cymbidium picture

The Genus Cymbidium

MANY PEOPLE THINK FIRST of a cymbidium flower when they hear the word 'orchid'. Cymbidiums are widely grown by orchid enthusiasts throughout the cooler parts of the world, and they form the basis of a significant cut-flower production. The flowers are long-lasting, both on the plant and when cut, large, attractive and available in a wide range of colours. Smaller plants are now coming into vogue as decorative pot plants. These have smaller flowers but they are as desirable as the standard varieties and often more acceptable in modern homes. In the East a number of wild species are prized for their attractive habit and sweetly scented flowers.

Most of the plants in commerce are hybrids, however. They have been derived, after more than a hundred years of artificial breeding, from only a few of the 44 known species. The search for novelty, which is ever-present in the orchid industry, has stimulated the use of some of the smaller flowered species in new hybridising programmes in the last 30 years with, in some cases, conspicuous success.

The practice of registration of orchid hybrids and their parents, which is managed by the Royal Horticultural Society on behalf of the international orchid community, demands accurate naming of plants. But this can be difficult, for botanists and growers alike, as the species were originally described in a wide variety of books and journals, over a long period of time, and often more than once.

Five years of research by David DuPuy, based on earlier work by Kit Seth and Phillip Cribb, resulted in the publication, in 1988, of The Genus Cymbidium. In the course of their work Cribb, Seth and DuPuy examined many hundreds of specimens, both living and preserved. They carried out field work in many of the countries where the species still occur in the wild. Weeks of work were spent in the laboratory making studies of anatomy and cytology. Each species was examined in the same way, in an attempt to gather together as much information as possible before coming to any decisions regarding classification and nomenclature. Illustrations were prepared by the artist Claire Smith when the plants flowered in the Living Collections Department at Kew. Finally, all the information was correlated and compiled into a PhD thesis by David DuPuy and then into an attractive account for publication as a book. It included two species new to science, discovered while the work was under way.

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What is a Cymbidium?

In preparing a monograph, one of the tasks of the botanist is to decide what to include and what to leave out. Inevitably, in the past, a number of species have been given the name Cymbidium but are now known to be better placed in other genera. Similarly, species which have not yet been transferred to Cymbidium may have to be sought in other genera. Before this can be done, the exact characters of the genus, features by which it can always be recognised, need to be elucidated and described. The characters traditionally used are those of vegetative and floral morphology. They are described briefly below.

The cymbidium plant is either epiphytic, lithophytic or terrestrial. Plants which normally grow on trees are sometimes encountered on rocks, and one species, C. macrorhizon, is a saprophyte which grows entirely beneath the soil surface except when the flower spike emerges. Most species have thick roots which are covered in a spongy white velamen and have only a thin core of vascular tissue. The erect stems are usually short and swollen to form a prominent pseudobulb which is often slightly flattened. Many species produce a new growth annually. In one section of the genus the pseudobulbs grow and flower for several years before a new shoot is produced, and in C. mastersii, C. elongatuni and C. suave, each shoot grows continuously for many years producing an elongated stem rather than a typical pseudobulb.

Each growth bears three to twelve leaves in two rows. The leaf lamina is articulated from the base by an abscission zone, where it will break after a few years when the leaves are shed. The pseudobulbs remain encased by the leaf bases. The leaves may be thick, rigid and leathery, as in C. aloifolium and its allies, but are more often flexible with prominent ribs. The shade loving species, C. lancifolium and C. devonianum have broad, elliptic leaves, and many of the forest epiphytes have long, thin and relatively narrow leaves.

The inflorescence in Cymbidium is unbranched and may be erect, arching or pendulous. Each mature pseudobulb usually produces one or two inflorescences from leaf axils near the base. (They are commonly called spikes but this is erroneous: botanically, they are racemes, because each flower has a short pedicel.) In C. eburneum and its allies the inflorescences arise from the leaf axils near the apex of the pseudobulb, as they do in C. suave and C. elongatum. The inflorescences bear up to 50 flowers in C. canaliculatum and only one in C. goeringii and C. eburneum. Most species bear 10-20 flowers.

The flowers are all immediately recognisable as cymbidiums. They comprise a dorsal sepal, two lateral sepals, two free petals and a three lobed lip which is hinged at the base of the column. There is usually a callus of two distinct ridges along the upper surface of the lip. The anther contains two pollinia or four pollinia fused in two pairs.

This brief summary can be applied to all or any of the species. Individually they can be much more precisely defined than this, and some species also vary to quite a large extent. Thus a large part of a monograph will consist of descriptions and illustrations of the individual species and their variation. Their distribution is mapped and habitat preferences recorded.

In attempting to understand the relationship between the various species, or postulate their possible evolution, several other kinds of evidence are assembled and considered.

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Leaf Anatomy

Features of the leaf which provide useful anatomical information for classification can usually be discovered by examination of its surface and by making transverse sections of the lamina.

The Scanning Electron Microscope (SEM) allows a picture of the micromorphology of the leaf surface to be produced without destroying it. In this study, the lower surface of the leaves was examined closely in order to study the arrangement of the stomata, the shape of the dome of cuticular material formed by their guard cells and the shape of the pore in this dome. Several different patterns of surface morphology were revealed, two of which are shown in the accompanying photographs. The patterns were characteristic of groups of species which seemed to be closely related.

Transverse section of the leaf of Cymbidium whiteae: fibres and stained red, cells with living contents stained blue

Transverse section of the leaf of Cymbidium whiteae: fibres and stained red, cells with living contents stained blue

Transverse sections of the leaves also revealed startling differences among the species, particularly in the distribution of the strands of supporting fibrous tissue. In C. aloifolium and its allies there is a complete layer of fibres immediately below the epidermis which link the larger bundles of fibres that strengthen the leaf.

In the subgenus Cyperorchis and in Cymbidium dayanum, the subepidermal layer is lacking and the fibrous strands are isolated from each other. These species also have smooth epidermal cells. In subgenus Jensoa, however, where the bundles of fibres near the lower surface are also isolated, the epidermal cells have a conspicuous papillose surface. The accompanying photograph shows part of a leaf of a member of the subgenus Cyperorchis. The small strands of fibres along the margins and the larger bundles surrounding the vascular tissues of the leaf are similarly arranged in all the species of this subgenus.

Scanning electron micrographs of the leaf surface of Cymbidium dayanum the lower epidermis

showing crowded stomata (magnification x80)

Scanning electron micrograph of the leaf surface of Cymbidium atropurpureum the lower epidermis showing scattered stomata (x 125)

single stoma and surrounding cells (magnification x750)

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Seed Structure

The SEM is also a useful tool for the examination of the tiny seeds of orchids. Photographs can be taken at high magnifications and often reveal significant differences between species or genera.
Scanning electron micrograph of seeds of Cymbidium atropurpureum - whole seeds, showung the fusiform shape and network of cells of the seed coat (magnification x80)

Scanning electron micrograph of seeds of Cymbidium atropurpureum - whole seeds, showung the fusiform shape and network of cells of the seed coat (magnification x80)

testa cells, showing junction of cells and striations on their surface (magnification x360)

At first sight the seeds of Cymbidium species are quite typical of the majority of orchids. They are minute, 0.5-1.9 mm long, and fusiform or filiform in outline. A spherical embryo, which is not visible in the photographs, is enclosed in a thin testa which is only one cell layer thick. The cells of the testa are few and large.

Two types of seeds were found among the species examined. Seeds of species in the subgenera Cymbidium and Cyperorchis are fusiform and 0.5-1.2 mm long. Their testa cells have longitudinal striations along the surface. This type of seed structure was also found in the seeds of several related genera, including Grammatophyllum, Ansellia, Eulophiella and Cymbidiella.

In subgenus Jensoa, however, the seeds were much narrower and 1.4-1.9 mm long. The striations on the surface of the testa cells in these species were transverse instead of longitudinal. This combination of characters is also found in some Asiatic species of Eulophia.

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Cytology

The diploid chromosome number in all species of Cymbidium was found to be 40. A few exceptions were the triploid or tetraploid, named cultivars of a few species, e.g. C. insigne 'Bieri' (2n = 60), C. floribundum 'Geshohen' (2n = 80) and C. floribundum 'Yoshina' (2n = 60).

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Cymbidiums in Cultivation

The beginnings of orchid appreciation and cultivation are found in the Orient. Confucius (551﷓479 BC) is recorded as saying that acquaintance with good men was like entering a room full of Ian, or fragrant orchids. The word lan is used for a wide variety of fragrant plants, but the lan hua that he referred to was almost certainly Cymbidium ensifolium. It is still cultivated in China and Japan, today, and displayed there in beautifully decorated containers whether or not it is in flower.

This species was also one of the first cymbidiums to appear in Europe. Linnaeus named it in his Species Plantarum in 1753, but under the genus name

Epidendrum. Live plants were first introduced by Dr. John Fothergill, on his return from a visit to China in 1778. They were sent to a relative in Yorkshire and flowered there quite soon afterwards. But they do not seem to have survived long or to have been propagated at that time.

It was the middle of the 19th century before. cymbidiums, among many other tropical orchids, were cultivated on a large scale in Europe, and especially in England. The best of the early accounts of them is given by Veitch in his Manual of Orchidaceous Plants. In Part IX published in 1893, he records that about 30 species of Cymbidium were then known, distributed from the Indo﷓Malayan region to tropical Australia and with outlying species in Japan and New Caledonia. Cymbidium ensifolium was apparently not cultivated in Europe when he wrote. Most attention was paid to the Indian species with larger flowers and the first hybrid which had been created in 1878 from C. lowianum and C. eburneum. It took nine years for the resulting seedlings to reach flowering size, and the Royal Horticultural Society gave its first Award to a Cymbidium hybrid, C. Eburneolowianum, in March 1889.

The first of the large-flowered cymbidiums to flower in English glasshouses was C. iridoides (syn. C. giganteum). It was introduced from the tropical parts of the Himalaya range and plants grew well at Chatsworth. The dull greenish brown flowers rarely open fully and are shorter﷓lived than those of some other species. The plants are relatively large and the combination of these features has made this species less popular with modern growers.

The white flowered C. eburneum was originally discovered in about 1837 and first flowered in an English nursery 10 years later at Loddiges in Hackney. For many years it was highly prized and rather rare in collections, but towards the end of the 19th century plants were imported in great quantity and widely cultivated. The waxy flowers are often scented but only one or two are borne on each peduncle.

Next on the scene was the green-flowered C. hookerianum (syn. C. grandiflorum). The first plant was seen in flower at Chelsea in the early 1850s and then not again until 1866. It was named by H C Reichenbach in honour of Joseph Hooker. It is an early flowering plant and has been used to breed some beautiful green-flowered hybrids which also flower early in the season. The species is rarely seen today and proves difficult to bring into flower in glasshouses because the buds are sensitive to heat. They stop growing and eventually fall before opening if the spikes are subjected to sudden changes of temperature.

Cymbidium lowianum appeared in flower in Low's nursery at Clapton in the spring of 1879. As a horticultural plant it was immediately welcomed. It proved easy to grow and was very floriferous in cultivation. It produced long arching racemes of brightly coloured, yellowish green flowers, chiefly remarkable for the V-shaped blotch of contrasting red or brownish colour on the lip.

Mixtures of orchid plants were not uncommon in those days of large importations. Cymbidium tracyanum first changed hands as a plant of C. lowianum, but when it flowered it was immediately recognised as distinct. The enormous flowers with their stripes of red-crimson dots along the sepals and petals, and sprinkling of reddish dots on the white lip, had a remarkable scent and appeared rather earlier in the season than those of other species, always before Christmas in temperate greenhouses.

A white-flowered species with distinctive red coloration on the lip and column is C. erythrostylum from Vietnam. First seen in flower in the west at Glasnevin in 1905, it is one of the smaller species but has large, long-lasting flowers which appear in the autumn. In the last 40 years it has been used to produce some superb hybrids with white, pinkish or light-colored flowers which are produced readily and in profusion, on plants of compact growth habit.

Pride of place among the species, for its contribution to hybridising, must be given to C. insigne. With its long upright spikes which have several white, pale or deep pink flowers near the top, it has been of extraordinary value as a parent in producing a wide colour range of well shaped hybrids. The most well known of these must be C. Alexanderi 'Westonbirt' (C. Eburneolowianum 'Concolor' X C. insigne 'Sanisters'), the first recorded tetraploid clone. It has exerted a tremendous influence in the breeding of shapely hybrids for more than 50 years.

Amongst the smaller growing plants, several species have become important in horticulture and especially in hybridising in recent years. The first to be used on any scale was C. floribundum (under the widely used synonym C. pumilum). Its erect, multi-flowered spikes of pinkish brown flowers with red markings on the lip are most attractive. Many plants with arching or pendent flower spikes have been bred from C. devonianum, an Indian species whose small flowers have a characteristic, dark velvety lip. The true miniature, C. tigrinum, has produced some charming hybrids, mainly with pale yellow flowers. C. ensifolium has come into favour again, and although the flowers do not last as long as those of other species and hybrids, they are sweetly scented and appear on slender upright spikes during the warm summer months, thereby greatly extending the flowering season for the genus. In China and Japan, selected clones of this and other native species and natural hybrids continue to enjoy great popularity among enthusiasts.

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New Classification

The most recent classification of the Orchidaceae which has been accorded wide acceptance among botanists is that of Robert Dressler (1981, and modified in 1986). He recognised six subfamilies in the Orchidaceae, with Cymbidium included in the Epidendroideae. Within this subfamily there are many tribes, including the Cymbidieae which contains all the sympodial vandoid orchids with similar seeds and two pollinia. By this criterion the subgenus Jensoa, with four pollinia, should not be included, but this single character seems insufficient to require its removal to another tribe.

Dressler placed Cymbidium in a small group of genera within the subtribe Cyrtopodiinae. All these plants have pseudobulbs of several internodes, articulated leaves, and usually a lateral inflorescence. The differences in structure of the pollinia and the whole pollinarium in Cymbidium and related genera are small but very interesting. The most similar is the African genus Ansellia, but that genus has a particulate inflorescence borne at the apex, not the base, of the greatly elongated pseudobulb.

The genus Cymbidium was established by Olof Swartz in 1799, based on Epidendrum aloifolium L. (= C. aloifolium (L.) Sw.). At that time he included many species which have now been transferred elsewhere, but two of his species, C. aloifolium and C. ensifolium, are still recognised. Many botanists have described individual species of Cymbidium since then, or have removed some of them to other genera, notably the genus Cyperorchis Blume. DuPuy and Cribb review this information and then present their own proposal. They propose the division of Cymbidium into three subgenera called Cymbidium, Cyperorchis and Jensoa respectively. Each of these contains several sections, in some of which there is only one, rather distinctive species. They distinguish these subgenera according to the formation of the lip and the number of pollinia. In Cyperorchis the lip is fused with the column base, while Jensoa, with four pollinia, has a free lip, as does Cymbidium, with two pollinia.

At the conclusion of their extensive study, DuPuy and Cribb considered that the genus Cyperorchis, which was distinguished by the Dutch botanist Blume and others because all the flowers have the lip fused with the base of the column, should be reunited with Cymbidium but maintained as a distinct subgenus within it. All the other species they classify in two further subgenera: Cymbidium, containing those where the anther bears two pollinia and Jensoa, whose species have four pollinia.

Exhaustive details of the 44 species, 7 distinct subspecies and 7 recognised varieties are recorded in the account of this painstaking work. Two new species, C. borneense and C. elongalum, and several new subspecies are described and illustrated. Some exciting stories have been unraveled concerning the early collections and importations, and the accounts of some of the rivalry between enthusiasts and their gardeners for these plants are enthralling reading. Historical difficulties of discovery and description are related and problems solved. Many names are shown to be synonyms, sometimes causing familiar names of widely grown species to be replaced by earlier names which have been neglected up to now.

Above all else this study demonstrates the importance of combining a knowledge of plants in the wild and the glasshouse with careful study in the laboratory, herbarium and library.

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