Structure of the Ginger plant

All Gingers are herbaceous plants. Even if some of them reach above 10 m height as the giant Alpinia boia from the Fiji Islands, others, such as some species of Kaempferia, are hardly raised more than a few cm above the ground. The Gingers are all perennials with a rhizome, an usually underground, leafless stem. From the base of the stem or from the rhizome roots are produced. In some species, mainly from the dryer regions, the roots are terminated by ellipsoid or spherical tubers with starch- filled cells. The rhizome may be long and straight as in most species ofHedychium, it may also be branched as in Zingiber. In species of e.g. Boesenbergia, Kaempferia, Globba and other low herbs the rhizome is mostly short. The terminal part of the rhizome or a branch of it turns upwards and becomes the leafy shoot. In some species of Amomum, Geostachys and Hornstedtia the rhizome is raised above the ground on stilt roots. In some species the rhizome is raised more than 1 m above the litter of the forest floor.

A real stem is present in most species but usually it is very short and higher up replaced by a pseudostem (“false stem”) formed by the leaf sheaths. In this book the term leafy shoot is used. The leaves are distichous (arranged in two rows) in all species. The leaves consists of a leaf sheath which is open to the base. In most species the lower leaves consists of this part only or with a diminuative lamina. The leaf sheath is terminated by the ligule, a membranous structure on the inner side of the sheath, it varies in length from less than 1 mm in Cornukaempferia to nearly 5 cm in some Zingiber species, mostly it is entire, but in Boesenbergia it is bilobed; very rarely the ligule is wanting. Above the sheath follows the petiole, a short or long stalk-like part after which follows the lamina or leaf blade. In the genus Zingiber the petiole has a part immediately below the lamina that is swollen, this is called a pulvinus, similar to a structure characterizing the Marantaceae. The lamina varies from few cm in some species of the Zingibereae to more than 1 nr in some Alpinia species. The base of the lamina vary from cordate to rounded or tapering towards the petiole, the tip from rounded to acute or acuminate. The vegetative parts may be glabrous or hairy in various degree or in some species of Zingiber covered by a glaucous, waxy layer.

The inflorescence is either terminal on the leafy shoot or borne on a separate shoot from the rhizome near to the leafy shoot or in some distance from it and then also called radical. In the genus Plagiostachys the inflorescence is terminal but breaks through the leaf sheaths in the lower part of the pseudostem. The inflorescence of all Zingiberaceae is in principle composed of partial inflorescences, these are of the cymose type and called cincinnae. In some genera, e.g. Hornstedtia and Etlingera, the inflorescence is sourrounded by sterile, leafy bracts called involucral bracts.

The cincinnae are subtended by bracts (sometimes, mainly in older literature, called “primary bracts”). In rare cases the cincinnae are reduced to single, sessile flowers (Alpinia oxymitra), in that case the inflorescence becomes a spike. Small leaf structures are often present on the pedicel (flower stalk) on the side opposite the main axis, these are the bracteoles (“secondary bracts”). The bracts may be free or joined at the base to pouches as in Curcuma, they may be spaced or densely overlapping as in Hedychium coronarium and in most Zingiber species giving the whole inflorescence a cone-like appearance. In many Curcuma species and in Smithatris the bracts, terminating the inflorescence, are sterile and of an other colour than the floriferous bracts, this structure is called acoma.

The ginger flower is highly specialized. It is always bisexual, i. e. having a stamen as well as a pistil. The flower is always superior, meaning that the ovary is situated below the perianth. Belonging to the Monocotyledones, the Zingiberaceae have basically 3-merous flowers consisting of 5 whorls, the two outer ones, the perianth, each with 3 leaves, then two inner ones, the stamens also with 3 each, and finally the ovary composed of 3 carpels. But that is not so easy to interpret in gingers (see page 24-26).

The outer whorl of the perianth is formed as a calyx tube, mostly split down one side and with 3 short teeth representing the 3 original sepals. It is a very delicate, filmy structure. The inner whorl, the corolla, consists of the corolla tube ending in the 3 corolla lobes (sometimes called petals). The dorsal lobe (the one placed closest to the axis) in usually slightly different from the lateral ones. Inside the perianth the stamens should be found. The Monocotyledones all have basically 6 stamens. In the Zingiberaceae only one is functioning as a reproductive organ. Two stamens are transformed to lateral staminodes; these may be free, petaloid as in Zingibereae and Globbeae or joined to the labellum in Zingiber as sidelobes or reduced to small dentate appendages to the labellum in Alpinieae. Of the remaining 3 stamens, one is reduced while 2 form the labellum (or lip). There is thus a big difference between the lip of an orchid where it is a true petal, while the lip of a ginger is staminodial. The only functioning stamen has a long or short filament terminated by the anther. The anther may be terminally fixed on the filament or it may be versatile. It consists of two pollen sacs connected by sterile tissue called the connective. In some genera e.g. Camptandra, Roscoea and many species of Curcuma the pollen sacs are provided with basal spurs, in others, like Kaempferia and Caulokaempferia, the connective is produced beyond the thecae into an anther crest. In Globba the anther is usually provided with lateral appendages of great importance for determination of the species. Innermost in the flower we find the pistil formed of 3 carpels as clearly is seen from the fruit. There is, however only one style and stigma. The two “missing” branches of the style is found on top of the ovary as stylodial glands producing nectar. The ovary is either 3-locular with the ovules placed on a central placenta or unilocular with the ovules placed on 3 placentas on the inside of the ovary wall (parietal placentation). The style is extremely thin and placed in a cavity on the backside of the filament, leaving only the stigma, usually funnel shaped, to be seen on top of the anther. In many species, and even some genera, the fruit is still unknown. Where known it is a dry or fleshy capsule, dehiscing in various ways or, in some species of Alpinia it is indehiscent. The sculpture of the fruit varies greatly and is of great taxonomic importance. In many species of Etlingera the fruits fuse to form a so-called syncarp, a large fleshy body reminding of a small pineapple or pandan syncarp. There is also a big variation in the size and form of the seeds. With only few exceptions the seed is provided with an aril (or arillus), a succulent tissue originating from the base of the seed. In some genera the aril is only partially covering the seed in others it covers the seed fully and may even join with the other arils in the locule of the fruit as seen in Hedychium where the aril is bright red. In most Gingers the aril, however, is whitish or almost translucent.