Zingiberales
- Related Topics:
- Zingiberaceae
- Marantaceae
- Strelitziaceae
- Musaceae
- Cannaceae
Zingiberales, the ginger and banana order of flowering plants, consisting of 8 families, 92 genera, and more than 2,100 species. Members of Zingiberales are widely distributed in the tropics, particularly as shade plants in tropical regions.
Several genera of the order are of major economic importance. Foremost are the hybrids of banana (Musa), which yield the edible banana and plantain fruits. Manila hemp, or abaca, is the name given to the strong fibres of the leaf stalks of M. textilis, an inedible banana native to the Philippines Islands. These fibres are made into ropes and twine. Arrowroot starch, used in special diets and in fine baking, is extracted from the rhizomes (stocky underground stems) of Maranta arundinacea, cultivated mainly in the West Indies. The rhizomes of Canna are also edible, but many cultivars in this genus are most noted for their showy flowers. Most plants in Zingiberaceae, or the ginger family, have aromatic leaves and flowers. Zingiber officinale yields true ginger; other genera are the source of additional spices, medicinal products, dyes, and condiments. A number of species are grown as ornamentals in greenhouses and can survive winters in mild temperate regions.
Families
The largest family in the order is Zingiberaceae, with 56 genera and more than 1,300 species. The family includes such important spices as ginger (Zingiber officinale), turmeric (Curcuma longa), tavaksira, or East Indian arrowroot (C. angustifolia), and cardamom (Elettaria cardamomum).
Musaceae, or the banana family, contains important fruit and fibre plants in tropical and subtropical areas of the Old World. It comprises two or three genera and about 50 species.
Marantaceae is known for a number of important commercial species: among them are West Indian arrowroot (Maranta arundinacea); various Calathea species, used as a source of wax, edible tubers, and flowers; and the prayer plant (M. leuconeura), grown as a decorative houseplant. The family contains 31 genera and 550 species.
Strelitziaceae contains one of the most spectacular ornamental plants, the bird-of-paradise flower (Strelitzia reginae). In addition, traveler’s tree (Ravenala madagascariensis), a dominant member of the tropical forests of Madagascar, is the largest member of Zingiberales, growing to a height of 8 metres (26 feet) and displaying a fan-shaped array of 20 or more leaves that are 4 to 5 metres (13 to 16 feet) long. The large flowers of Strelitzia are thought to be bird-pollinated.
Cannaceae, a family with a single genus (Canna), is known for the starchy edible tuberous rhizomes of achira (C. discolor) and Indian shot (C. indica).
The three remaining families in the order—Heliconiaceae, Lowiaceae, and Costaceae—are primarily of horticultural interest.
General features
Within Zingiberales, many of the plants and their leaves are very large. They are herbaceous perennials in the sense that most of them have little or no woody tissue; in the wet tropics they are evergreen. Because their stems do not develop secondary vascular tissues, their possible growth habits are restricted, but within these limits they are remarkably varied.
Traveler’s tree (Ravenala madagascariensis) and related plants develop thin stems surmounted by the current crop of leaves. Encircling scars indicate the position of leaf sheaths already shed by the mature stems. The most common type of stem in Zingiberales is short and below ground. In many gingers, all leaves arise at ground level, their clasping sheaths and leaf bases hiding the stem. In the bananas, the vegetative stem is a stocky subterranean structure that extends above the level of the soil for a short distance; it is surrounded by massive leaves and is never visible. Each new leaf grows inside the sheath of the preceding one. One edge of the leaf overlaps the other, resulting in a slight dwarfing of the edge that is lowermost. What appears to be the stem of the banana plant is, in reality, a false trunk consisting of many leaf sheaths that are rolled up longitudinally to form a cylinder.
In Zingiberales, branches arise from underground stems and are known as rhizomes (when elongate) or suckers (when short and bulky); they produce leaves and eventually emerge above the surface of the soil. When separated from their parents, such units reproduce the species vegetatively. This method of propagation ensures the perpetuation of desirable genetic traits; if grown from seed, some expected qualities may be replaced by others that are not as desirable.
Inflorescences
Zingiberales flowers have three sepals, three petals, up to six stamens in two whorls of three each, some being represented by sterile structures of varying form, and three carpels; the members of successive whorls are alternating. The female structure, or ovary, is enclosed by the united basal portions of the other flower parts, which thus appear to arise at the upper end of the ovary (an inferior ovary). The calyx is always different in shape and size from the corolla, and the sepals are free from each other in all families except Zingiberaceae, which has a tubular calyx with small free lobes. The flowers are mostly bilaterally symmetric (zygomorphic), but in some cases they are asymmetric. There are six stamens only in the genus Ravenala; the rest of the order exhibit either five stamens (four families) or one functional stamen, the other stamens represented by a varying array of petal-like sterile stamens called staminodes, which form the conspicuous part of the flower (four families).
Variations on the basic flower structure pattern exist in the families with five and with one stamen. In the former, sepals and petals are the conspicuous parts of the flower; they are often large, and the paired petals are larger than the median one except in the genus Musa and the family Lowiaceae. The families with one stamen and a varied number of petal-like staminodes show a great range of floral form. The most conspicuous part of the flower in the family Zingiberaceae is usually called the labellum; this structure, however, does not consist of the same floral parts as the labellum in the family Lowiaceae and in orchids, in which it is a petal. The labellum represents two or three united stamens, and in many genera there is a pair of smaller but conspicuous petal-like staminodes, each representing one stamen (in the genus Zingiber they are joined to the labellum); the result is a flower of orchidlike aspect, but the parts concerned in orchid and ginger flowers are different, and undoubtedly the two have developed along quite different evolutionary lines. In the families Marantaceae and Cannaceae, the single stamen is only half functional, the other half being more or less petal-like. In both families, the staminodes are of varying size and shape, so their status is not easily decided, and there have been differences of opinion about them. In the family Costaceae, the large labellum represents a union of all five nonfunctional stamens, and in some cases it can be seen to be five-lobed.
In species that flower at the top of leafy stems, such as cardamom (Elettaria cardamomum), the main inflorescence bracts are often small or lacking, and the flowers are fully exposed. The inflorescence develops inside the tube of overlapping leaf sheaths and appears at the top of the plant with flowers fully formed; the leaf sheaths thus take over the protective function of the main bracts. All members of the family Zingiberaceae have brightly coloured flowers and slender flower tubes full of nectar. They are probably mostly pollinated by butterflies. Flowers are, in all cases, short-lived, often lasting only a few hours.
In Southeast Asia, many members of the family Zingiberaceae that have tall leafy stems produce their flowers on separate short sheath-covered stems that arise from buds on the rhizome; the flowers are protected by overlapping bracts, the whole inflorescence often being shaped like a pinecone. In species having long rhizome elements, the inflorescence may appear some distance from the nearest leafy stem.
In the genus Hornstedtia (family Zingiberaceae), the inflorescences are wholly just above ground level, with firm empty outer bracts forming a spindle-shaped structure out of the top of which the flowers emerge, one or two at a time. In one Malaysian species of Hornstedtia, however, the whole rhizome is raised 50 cm (20 inches) or more above the ground by thick red stilt-roots, so that the flowers are also raised. In nearly all such inflorescences, the overlapping bracts hold water in which flower buds and, later, fruits develop. Alternatively, moisture may be provided by the rotting of main bracts (e.g., in some species of Amomum, another genus in the family Zingiberaceae), so that fruits develop in a mass of black putrescence maintained in a wet state by frequent rains.
In the genus Etlingera (family Zingiberaceae), the inflorescence shoots are often so short that they do not emerge from the ground and all that can be seen is a circlet of flowers with prominent bright red petal-like structures (labella) radiating outward, the flower tubes and ovaries being below ground level. Fruits ripen below ground, and the seeds are thought to be dispersed by wild pigs or other animals. The leafy shoots may be 3–5 metres (10–16 feet) tall, so that the leaves are high in the air, even though the flowers are partially buried in the ground.
Musa flowers are individually not conspicuous, but the large main bracts are quite conspicuous; the bracts curl back in turn to expose the flowers they have protected while in bud. Musa species (including cultivated bananas) with pendulous inflorescences and dull purplish bracts have flowers with a rank odour and copious nectar; they open at night and are pollinated by bats. An important character of the cultivated bananas is that fruits develop without pollination; if pollinated by bats (as they often are), they do not form seeds. Other species of Musa have erect inflorescences and brightly coloured bracts; these appear to be bird-pollinated, though the flowers are also visited by bees for pollen.
The small flowers of the family Marantaceae, usually white, have a curious mechanism that is little understood but is doubtless connected with pollination by small insects. The style develops an internal tension but is held straight by the hooded staminode; when the latter is touched, the style escapes and instantly bends so that the stigma (the sticky pollen-receiving surface) faces downward. Pollen is deposited from the ripe stamen on the style below the stigma before the flower opens and may be removed by a visiting insect, but self-pollination is impossible.
The curious genus Orchidantha (family Lowiaceae) consists of rather small plants found in wet tropical forests. One species has quite large flowers with dull purplish sepals and creamy white labellum, both as long as 12 cm (5 inches). The flowers have a strong unpleasant odour and attract flies and dung beetles. The ovary has a long solid neck or prolongation to which the other parts of the flower are attached.
Richard Eric Holttum W. John Kress