Classification of Rhamnales: 2 Families | Dicotyledonae

In this article we will discuss about the classification of Rhamnales. According to Engler, Rhamnales consists of two families:- 1. Rhamnaceae 2. Vitaeae.

Family # 1. Rhamnaceae:

Rhamnaceae are trees or shrubs, often armed with spines, or climbers, climbing by hooks or ten­drils or twining stems, rarely herbs. Leaves are simple, stipulate, alternate or rarely opposite. Inflorescence an axillary cyme or cymose panicle or corymb.

Flowers are hermaphrodite, rarely unisexual regular, peri- or epigynous, usually minute. Calyx 4-5-lobed; lobes valvate, usually internally ridged. Petals 4-5, free, inserted on the calyx-tube forming a hypanthium, usually clawed and hooded, rarely petals absent.

Stamens as many as petals and opposite to and enclosed by them; inserted on the hypanthium or on the margin of an intrastaminal disc. Carpels 2-4, syncarpous, forming a 2-4-celled, peri- or epigynous ovary; ovule 1, rarely 2 in each cell, basal, anatropous, with dorsal raphe; style 1 or 2, short; stigma simple or bilobed; rarely ovary 1-celled.

Fruit a capsule or berry or samaroid; seeds with fleshy endosperm or rarely without endosperm and large straight embryo.

The spines in Zizyphus are stipulary in nature. Colletia and Condalia have thorns which are modified branches. Colletia spinosa Lam. has thorny shoots with small cadu­cous leaves although at seedling stage it bears normal foliage leaves. Gouania, Helinus and Reissekia are tendril-climbers, the tendrils being metamorphosed branches. Ventilago is a large twiner. Leaves palminerved in Zizyphus but pinninerved in other genera.

In Microrhamnus and in a few species of Rhamnus flowers are solitary and axillary. In Gouania flowers are polygamous. Rhamnus cathartica Linn, is dioecious. Hovenia dulcis- Thunb. has fleshy peduncle. Flowers of Berchemia scandens Trel. are hypogynous and have no hypanthium.

Apetalous flowers occur in some species of Colletia. In Paliurus the base of the style develops into a large broad rim like that of a hat. Fruit is a capsule in Phylica, Pomaderris, etc. a juicy drupe in Rhamnus, Zizyphus etc. while Gouania and Ventilago have samaroid fruits.

The stomata are of Ranunculaceous or Rubiaceous type. Secretary cells con­taining tannin and mucilage occur in primary cortex. Vessels have simple perforations and intervascular pitting is alternate. Wood parenchyma is paratracheal. In Zizyphus the stem has continuous sclerenchymatous pericycle while in others the pericycle is made up of isolated strands of fibres.

The family consists of about 550 species under 45 genera occurring in the tropical and temperate parts of the world. Rhamnus and Zizyphus are widely distributed, the former occurs in America, Europe and extra tropical Asia while the latter, although mainly. Indomalayan, is found in Africa and spreads eastwards to Australia.

Collena is found in S. America and Pomaderris is an Australian genus. In India 53 species occur in the plains as well as in the hills, e.g. Rhamnus virgata Roxb. R. nepalensis Wall. ex. M. Laws., Ventilago maderaspatana Gaertn., Zizyphus mauriliana Lam., Z- oenoplia Mill, Gouania leptostachya DC., etc.

Several species of the family are economically important. Jujubes are the drupes of Zizyphus mouritiana Lam. (Baer of India, Beng. Kool.), Z- jujuba Mill., Z- vulgaris Lam., etc. Z. mouritiana Lam. is cultivated in India and Western Asiatic countries and also grows wild.

It is also used for rearing lac insects. Rhamuspurshiana DC. of N- America yields the Cascara sagarda bark—a purgative, while the bark of R. chlorophora Dene, yields a green dye. Root-bark of Ventilago maderaspatana Gaertn yields red dye.

Dye is also obtained from the fruits of R. infectoria Linn. Frangula alnus Mill, is the Dogwood, the charcoal obtained from which is much valued for making gun-powder.

The bark of this species is also used as purgative. Zizyphus mauritiana Lam. yields wood also suit­able for making gun-powder. Maeosopis emini Eng. of E. Africa yields good timber. Leaves of Ceanothus americanus Linn, and Sageretia thee zans Brong. are used as substitute of tea.

The family Rhamnaceae is very close to Vitaceae (and also to Leeaceae when it is treated as a distinct family) and the two families constitute the order Plwinihlui which forms a natural taxon. Rhamnaceae is also allied to Celastraceae to some extent and the orders Celastrales and Rhamnales are placed close to each other by most taxonomists.

Family # 2. Vitaceae:

Vitaceae are extensive climbers with leaf-opposed tendrils, rarely erect shrubs or small trees nodes often swollen or jointed. Leaves are alternate, the lower often being opposite, simple or pinnately or palmately compound, pellucid punctate, with petioiar stipules or mastipulate, usually distichous.

Inflorescence is a leaf-opposed cymose panicle, often very large with numerous minute flowers or corymbose and terminal; bracteoles present.

Flowers are usually hypogynous, actinomorphic, bisexual or unisexual in polygamo- monoecious or polygamo-dioecious plants, 5-4-merous. Calyx gamosepalous, cupular, entire or shortly 5-4 toothed. Petals 5-4, minute, valvate, free or connate, caducous, flat or with hooded incurved apex; often corolla obsolete. Intrastaminal disc promi­nent, annular or lobed or glandular.

Stamens as many as petals and opposite to them, free or connate at base inserted below the disc; anthers distinct or connate, dehiscing longitudinally. Ovary superior, 2-8-carpelled and 2-8-celled; ovules 1-2 in each cell on axile placentation, anatropous, ascending with ventral raphe. Style, short, stigma discoid or capitate. Fruit a berry. Seed with hard testa, copious ruminate endosperm and small straight embryo.

Most genera are vines; Carameriana is a tree while Leea has trees, shrubs and erect herbs. The tendrils are leaf-opposed and are interpreted by Eichler as the metamorpho­sed apical part of the sympodial stem. The inflorescence replaces the tendril.

In Cissus quadrangularis Linn, the internodes are 4-angled and succulent. The peduncle in Pterisanthes is flat and ribbon-like. In Vitis petals are free near base and united by the apices and falling off early as a cap. The filaments of stamens in Leea are united to form a 5-lobed tube.

The tendril in Vitis is negatively phototropic and thus forces its way into crevices of the support running away from the light. The ends of the tendrilar branches expand to form ball like structures which become sticky and mucilaginous and as a result the tendril adheres firmly to the support.

The leaves have globular and shinning stalked emergences known as ‘pearl glands’. These bear the stomata which are of ranunculaceous type. Most of the cells contain raphide crystals and mucilage cells are also common. The disc sometimes functions as nectaries to attract the insects which pollinate the flowers.

The floral formula of a hermaphrodite flower may be expressed as:

The family comprises 11 genera and about 750 species. The plants are found in the tropical regions of the Old- and New-World. Some are xerophytic succulent plants occurring in the drier parts of Africa and S. America.

There are about 70 species in India mostly growing in the plains, e.g. Ampelocissus latifolia Planch, Cissus repens Lam., C. adnata Roxb., C. quadrangularis Linn., Cayratia pedata (Wall.) Gagnep., Leea macro phylla Roxb., Vitis vinifera Linn. etc.

Stem anatomy shows that the vessels are large in all genera except Leea; perfora­tions are simple or scalariform. A more or less continuous ring of fibres constitute die pericyle with a few isolated strands. Medullary rays are long and broad and paren­chyma paratracheal. Abnormal secondary growth occurs in Cissus and Tetrastigma.

The family gains importance from the grape-vine,—Vitis vinifera Linn, with its innumerable varieties, originally of W. Asia and Mediterranean region now cultivated in almost all countries of the world. Raisins and currants are dried fruits of different varieties of this species. V. labrusca Linn, and V. aestivalis Michx of N. America produce edible berries inferior to grapes. A few others have medicinal properties.

The family is closely allied to Rhamnaceae and together with that family constitute the order Rhamnales which is a natural taxon according to most taxonomists. Some recent workers are in favour of segregating the genus Leea from Vitaceae and placing it in a distinct family of its own, viz. Leeaceae.

The family Leeaceae may be briefly described as having following characters: Erect shrubs or herbs or small trees. Leaves alternate, simple or pinnate, often bi- or tripinnately compound; petiole dilated at base to form 2 sheathing expansions or auricles, exstipulate. Cymes corymbose, leaf opposed or terminal. Flowers 5-merous, hypogynous.

Stamens outside the annular disc’ united in a 5-lobed tube with 5 free filaments arising between the lobes; anthers free and exserted from or connate and included in the tube. Ovary on the disc, 3-6 locular with a solitary ovule in each locule. Fruit a berry, depressed at the apex. Seed with hard testa and minute basal embryo and cartilaginous endosperm.

Comparison of Vitaceae and Leeaceae when treated as 2 distinct families: