Classification of Urticales: 3 Families | Dicotyledonae

In this article we will discuss about the classification of Urticales. According to Engler and Prantl, Urticales consists of three families:- 1. Ulmaceae 2. Moraceae 3. Urticaceae.

Family # 1. Ulmaceae:

Ulmaceae are trees or shrubs, often with mucilage, evergreen or deciduous. Leaves of Ulmaceae are simple, stipulate, distichous, often with asymmetrical blades; stipules caducuous. Flowers of Ulmaceae is minute, unisexual or rarely polygamous, solitary or in cymose clusters. Perianth in one whorl, sepaloid, persistent, with 4-5 members or sometimes upto 9, free or connate, imbricate, rarely valvate.

Stamens as many as perianth segments and opposite to them, rarely, fewer; filaments erect; anther bilocular, dehiscing longitudinally.

Ovary bicarpellate, unilocular, rarely 2-locular; styles 2, divergent, stigmatic on their inner sur­faces; ovule solitary in each chamber, pendulous from near the top. Fruit a samara or drupe, rarely 2-seeded; seed with a straight or curved embryo and with no endosperm or with scanty endosperm; cotyledons rarely unequal.

Ulmaceae is a small family with about 150 species in 15 genera distributed in the tem­perate as well as tropical regions. Although a comparatively small family it shows a wide range of variations. Ulmus the Elms and Holoptelea are deciduous, while others are evergreen.

Unisexual flowers generally occur, but bisexual flowers also occur in some genera along with unisexual flowers. Leaves are penninerved or with 3-7 prominent veins from the base, as the Celtis and Trema.

Ovary is usually sessile but stipitate in Holoptelea. Celtis has a curved embryo’ while others have straight embryo. The fruit of Ulmus, Holoptelea etc. is a samara while in Celtis, Trema and others it is a drupe.

The timber obtained from the Elms is good. Planeta abelica Gemel (= Zelkova cretica Spach.) has fragrant wood which is known as False Sandal wood. Wood of Trema and others make good charcoal. In India the family is represented by a few species of Ulmus, Holoptelea, Celtis and Trema.

Ulmaceae is closely related to the other 2 families of the order, viz., Moraceae and Urticaceae. Hutchinson splits Ulmaceae into Ulmaceae and Barbeyaceae with a single species and this is maintained as a distinct family by the recent workers.

Family # 2. Moraceae:

Moraceae are trees or shrubs, rarely climbing and very rarely herbs, with milky latex. Leaves of Moraceae are simple, alternate, stipulate; stipules usually large and covering the leaf bud, caducous; often cystoliths are present in leaf epidermis. Flowers of Moraceae is unisexual in monoecious or dio­ecious, mainly cymose head like inflorescences or condensed spikes, bracts often present.

Perianth sepaloid, usually 4 in 2 whorls, rarely 2 or 1, persistent, very small. Stamens as many as sepals and opposite to them, or only 2 stamens or rarely 1; filaments straight or incurved in bud; anthers usually versatile.

Carpels 2; ovary superior, one chambered or two-chambered, one chamber with a pendulous ovule and the other empty; styles 2 or rarely 1, short, with a bifid stigma; ovule curved. Fruit a drupe or a multiple of achenes or berries. Seeds with usually curved embryo and with fleshy endosperm, or endosperm absent.

In Moraceae family the flower-structure as well as the inflorescence shows great varia­tions in different genera. Broussonetia is dioecious, the male spikes are borne in plants which never produce the female flowers which are in globose heads on different trees. Morus may be monoecious or dioecious.

Streblus is usually dioecious; the males in spikes which may be elongated or condensed into a head while the female flowers are solitary or 2-4 together. Cannabis (now included under Cannabinaceae) is dioecious; the male flowers in paniculate cymes and the females in short racemes.

In Ficus the peduncle enlarges in the form of a vessel enclosing the male and female flowers as well as some sterile female flowers known as the gall-flowers. This type of inflorescence is called hypanthodium. Another special type of inflorescence is found in Dorstenia where peduncles of several cymes unite to form a flat saucer-shape structure with both type of flowers in the central portion.

Stamen solitary in Artocarpus and usually so in Ficus; in most genera the number is 4 while in Cannabis there are 5 sepals and 5 stamens. Filaments of stamens inflexed in bud in Streblus, Morus, Broussonetia, etc. but erect in Balanostreblus, Artocarpus, Ficus, Cudrania, etc. Fruits are simple achenes in Streblus, Conocephalus, Taxotrophis etc. but multiple or aggregate fruit occurs in many genera.

In Ficus the whole hypanthodium matures into a fruit. In Artocarpus the whole female inflorescence including the club- shaped receptacle turns into a fruit which is a sorosis. Usually the seeds have 2 equal cotyledons but in few genera, e.g. Phyllochlamys, Streblus, Artocarpus, etc. one cotyledon is much larger than the other.

Flowers are entomophyllous. In Ficus where the flowers are enclosed within the hypanthodium, these are pollinated by the insect Blastnphaga which enters the hypanthodium through an opening at the apex. The insect lays eggs in the ovary of gall flowers where the style is much shorter than that in the normal female flowers.

The fertile female flowers have long style with papillose stigma. The insect while moving inside the hypanthodium collects pollen from the stamens of the male flowers and the papillose stigma of the female flowers catches them from the body of the insect.

Many species of this family are economically important. Ficus carica Linn, produces the edible fig and is cultivated in the Mediterranean region and W. Asia. Ficus glomerata Roxb. (=F. racemosa Linn.) is Jagnya Dumur or Gular which is cooked as vegetable and taken raw when ripe. F. hispida L. f. is also used as vegetable and is called Dumur in Bengal.

Ficus clastica Roxb. of eastern India yields a latex suitable for manufacturing rubber. F. benghalensis Linn, is the Banyan tree and F. religiosa Linn, is the Aswattha or Pipal tree usually planted in villages as shade trees. Artocarpus heterophyllus Lam (Syn. A. integrifolia L. f.) is the Jack fruit and A. incisa Linn, is the Bread fruit-tree. A. lakoocha Roxb. is the Dehu or Deo phal, the ripe fruit of which is also edible.

The timber of most Artocar­pus and particularly of A. heterophyllus and A. Chaplasha Roxb. is very valuable. Morus is a small genus different species of which are cultivated to feed silk worms with their leaves. Morus nigra Linn., M. alba Linn, and M. australis Poir produce delicious fruits.

The timber obtained from the species that attain tree-size is hard and is used in many ways. Brosimum galactodendron H. B. & K. of Venezuela yields copius latex which is sweet and nutritious and taken as milk.

The tree is known by the name “Cow-tree”. Streblus asper Lour a short tree grows wild in tropical Asiatic countries the leaves of which are very rough and are used to polish ivory; the branches are much used as tooth brushes, the latex being good for the gum.

The fibre obtained from the bark of Broussonetia papyrifera Vent, is woven into a coarse cloth and also used to manufacture paper and cardboard. Antiaris toxicaria Lesch.—the Upas tree, the latex of which is used as arrow-poison, has a bark which is, the Baikal or a coarse type of cloth worn by the poorer people.

The family with a little over 1000 species in about 72 genera is distributed mainly in the tropical countries. Ficus is the largest genus having about 600 species.

The Moraceae family is subdivided into 4 tribes as noted below:

I. Moroideae.

II. Artocarpoideae.

III. Conocephaloideae.

IV. Cannaboideae.

The last tribe, e.g. Cannaboideae, differs from the other tribes in having aromatic herbaceous plants without milky latex. It has simple nuts while in other tribes there is an aggregate or multiple fruits. For this reason many prefer to raise this tribe to a dis­tinct family as Cannabaceae (or Cannabinaceae or Cannabidaceae).

Cannabaceae:

(Cannabinaceae or Cannabidaceae)

Aromatic herbs or herbaceous climbers; milky latex absent. Leaves palmate or palminerved; stipules persistent. Flowers unisexual and dioecious or in Humulus sometime monoecious; inflorescence axillary, of a thyrsus type with an indefinite main axis and cymose clusters; the ♂ loosely many-flowered while the ♀ dense and few-flowered; bracts and bracteoles present.

Periapth in male flower 5-lobed, cup-like in female flower surrounding the base of the ovary. Stamens 5, opposite to the perianth lobes. Ovary superior, unilocular with one pendulous ovule; styles 2 with brush-like stigma. Fruit a nut; seed with scanty fleshy endosperm and curved embryo.

The family contains 2 genera and 3 species occurring in temperate and subtropical regions of the old world and are cultivated. Cannabis sativa Linn, is the Hemp, useful for its long and strong bast fibres. This plant is however more reputed for the narcotic resin it yields which is used in the preparation of an intoxicating drink known as Hashish or Bhang or Siddhi.

The female inflorescence with the resin is smoked and is called Gania. The bracts and bracteoles of Humulus lupulus Linn, bear numerous resinous glands which are aromatic and sedative and the floral-heads are used to flavour beer.

Family # 3. Urticaceae:

Urticaceae are herbs or shrubs, rarely climbers; watery sap present; many with stigning hairs. Leaves of Urticaceae is simple, alternate or opposite, stipulate; cystoliths often present in leaf-epidermis.

Flowers of Urticaceae is very small, unisexual monoecious or dioecious rarely polygamous in cymose clusters on short axillary shoots, often crowded in heads, rarely catkin-like. Perianth of 4 sepaloid segments, rarely 5, in 2 whorls; free in male flowers, more or less connate and persistent in female flowers.

Stamens of Urticaceae is as many as perianth segments and opposite to them; filaments inflexed in bud but spring elastically outwards when flowers open discharging the pollens in clouds; anthers bilocular, opening by longitudinal slits.

Ovary superior, of one carpel, 1-celled, with one erect, orthotropous ovule; style ends in a plumose stigma; rarely ovary inferior. Fruit an achene or drupe; seed with oily endos­perm and straight embryo.

The family includes many species possessing stinging hairs—the stinging nettles, e.g. Fleurya interrupts Gaud, species of Urtica, Girardinia, Laportea, etc. Laporten crenulata Gaud, is the Devil- or Fever-nettle of the Terai-region of the Himalayas, the slight touch of which brings severe irritation and pain all over the body often resulting in fever.

These nettles have hairs of which the apex is knob-like. The apex breaks very easily on coming into contact with animal body and the poisonous acid-sap contained in the hair is ejected and falls on the skin of the animal and produces irritation.

The plants of the Urticaceae family are more or less uniform in characters although some variations are noticed. In Parietaria bisexual flowers occur along with unisexual flowers. Here the inflorescence is often a biparous cyme. In Forskohlea perianth is absent or much reduced.

In this genus the male flowers have only one stamen. The peculiar feature in the family is the elastic nature of the stamens which throw off the pollens in the form of cloudy mass by their sudden movement.

The Urticaceae family consists of 42 genera and about 600 species occurring in tropical and temperate countries. It is represented in India by several species of Girardinia, Elatostemma, Pouzolzia, etc. Boehmaria nevea Hook. & Arn. grows in N. Bengal and is cultivated in eastern India and China for its fibre which is known as Rhea or Ramie-fibre.

Otherwise the Urticaceae family is not of much economic importance. The Urticaceae family is closely related to the other families of the order and is considered ad­vanced over others for having mainly herbaceous plants, monocarpellary ovary and basal ovule.