Classification of Contortae: 7 Families | Dicotyledonae

In this article we will discuss about the classification of Contortae. According to Hutchinson, Contortae consists of seven families:- 1. Oleaceae 2. Loganiaceae 3. Buddlejaceae 4. Gentianaceae 5. Menyanthaceae 6. Apocynaceae 7. Asclepiadaceae.

Family # 1. Oleaceae:

Oleaceae are trees, shrubs or undershrub’s, often scan-dent or twinning. Leaves are opposite, simple or pinnately compound, exstipulate, often pubescent with peltate hairs. In­florescence is usually cymose, often paniculate, rarely recemose; the cymes often form a dichasium.

Flowers are actinomorphic, bisexual, rarely unisexual, hypogynous, frag­rant or not. Calyx gamosepalous, 4-6 lobed, or entire at apex; lobes valvate; rarely calyx absent. Petals 4-5, connate below to form a salver-shaped or rotate corolla, or petals free, imbricate or valvate; rarely petals absent.

Stamens 2 or rarely 4, epipeta­lous on corolla tube, or hypogynous when petals free or absent; anthers bithecal oblong, dehiscing laterally or sub extrorsely, filaments short. Ovary bicarpellary, syncarpous, 2-chambered, superior; ovules usually 2 in each chamber, anatropous, pendulous or ascending; style short, stigma 2-lobed.

Fruit a berry, or drupe, or capsular, rarely a schizocarp or samara. Seed with copious fleshy endosperm and straight embryo, or endosperm absent; testa thin or bone-like.

Olea, Ligustrum, Fraxinus, etc. are trees, Jasminum is a genus of shrubs, often scan- dent or twining. Simple leaves are found in Olea, Linociera, Ligustrujn, etc. but Fraxinus, Schrebera, etc. have pinnate leaves.

Inflorescence in Jasminum is a true cyme, often a dichasial cyme; in J. nudiflorum flowers remain united in threes at the end of scaly shoots. Compound racemes are found in Ligustrum and Fraxinus. Flowers are unisexual in Fraxinus and also in some Olea. In Fraxinus either calyx or corolla or both may be absent.

Perianth segment usually 4 in each whorl but petals may be 5 or sepals and petals may be upto 7 or 9 even 10, as in some Jasminum, Nyctanthes and Schrebera. Ovary has 2 ovules in each chamber Out in Forsythia ovules may be 4-10 in each cell of ovary. In Hesperella and Tessarandra stamens are 4.

Extra floral nectaries in the form of peltatp hairs are found at the base of the flowers in some genera. In the axils of leaves several buds are sometimes arranged one above the other; these are accessory buds. In Syringa the winter bud has a scale which is considered as the sheath of the undeveloped leaf.

The vessels in the wood are small, solitary or in multiples of 4 or more cells, usually ring porous. Fibres are simple and bordered pitted. Pericycle is a continuous ring of fibres or of isolated strands of fibres. Wood parenchyma apotracheal or paratracheal. Vascicentric tracheids are present in a few genera.

The typical floral formula is:

The family with about 500 species under 21 genera are found in the temperate and tropical regions, a few genera confined to the Indo-Malayan region. Many Species of Jasminum occur wild in India and a few are cultivated, e.g.

J. sambac Ait.-Beli, J. auriculatum Vahl-Juthi, J. grandifloram Linn.—Chameli, etc. Nyctanthes arbor-tristis Linn. —Shefali grows wild in forest and is also cultivated. Fraxinus floribunda Wall, is a timber yielding tree of the Himalayas, Schrebera sweitenioides Roxb. with large woody capsules grows in Orissa.

Oleaceae is related to Loganiaceae to some extent. It is allied also to Apocynaceae in some respects. Hutchinson traces its affinity to Rubiaceae and Melastomaceae. Cronquist considers it to be allied to Buddlejaceae and includes Oleaceae in Scrophulariales.

Oleaceae is divided into 2 subfamilies as noted below:

Subf. I. Oleoideae:

Seeds pendulous; fruit not vertically constricted.

Subf. II. Jasminoideae:

Seeds erect; fruit divided into 2 parts by a vertical constriction.

The genus Nyctanthes of the S.f. Jasminoideae was transferred to a monotypic family Nyctanthaceae by Agardh while Airy-Shaw transferred the genus to Verbenaceae.

The family includes a few plants of economic importance. Olea europaea Linn, of the Mediterranean region is the Olive tree from the seeds of which the olive oil is obtained. Fraxinus excelsior Linn, yields the Ash wood of commerce.

Other species of Fraxinus are equally good timber trees. A dye is obtained from the orange tubular part of the corolla of Nyctanthes arbvrtristis Linn. Many species of Jasminum are cultivated for fragrant flowers and a few yield essential oil.

Family # 2. Loganiaceae:

Loganiaceae of Engler and the older workers was splitted to 6 families by Hutchinson, viz. Potaliaceae, Loganiaceae, Buddlejaceae, Autoniaceae, Spigeliaceae and Strychnaceae. Cron­quist recognises Buddlejaceae as a distinct family but does not treat Potaliaceae, Auto­niaceae, Spigeliaceae and Strychnaceae as separate families. Loganiaceae of Cronquist is a larger family that includes the above 4 families of Hutchinson.

The conscription of Loganiaceae as understood by Cronquist is given here.

Loganiaceae are trees, shrubs or herbs, often climbing. Leaves are simple, opposite or whorled, stipu­late; stipules interpetiolar, or interpetiolar, often very minute or very rarely absent. Inflorescence cymose, often paniculate.

Flowers are hermaphrodite, actinomorphic, hypogynous, 4-5-merous; bracts and bracteoles present. Calyx 4-5-lobed or toothed, imbricate. Petals 4-5, united to form a tubular, semi-rotate or campanulate corolla, imbricate or valvate or contorted, often hairy at the throat or at the mouth inside.

Stamens 4-5, epipetalous, inserted on the corolla tube or on the mouth of corolla, alter­nating with the petals; anthers bilocular, introrse, dehiscing longitudinally; very rarely stamen one only.

Carpels 2, united to form a syncarpous bilocular ovary; ovary superior with numerous ovules in each chamber on axile placenta; style simple, stigma capitate or bilobed; rarely ovary unilocular with parietal placenta. Fruit a berry or drupe, or a capsule. Seed without endosperm and with a straight embryo.

Strychnos is a genus of trees but a few species are tendril climbers. Species of Fagraea are also climbers and some are epiphytes. Gelsemium is a stem-twiner. Mitreola and Mitrasacme are small herbs. Leaves of Strychnos are 3-5-nerved.

Cymes in Mitreola are 2-3-chotomous, in Mitrasacme often in umbels and in Fagraea sometimes grouped in corymbs. The size of flowers varies great. Mitreola has flowers which are about 2 mm. long, while Fagraea auriculata Jack has flowers about 20 cm. long and 30 cm. across.

Numerous bracteoles are present below the flowers in Gelsemium. In Usteria the flower has a single stamen. Ovary in Mitreola is semi-inferior. In Strychnos the ovary is uni­locular and the placentation is parietal.

Floral formula of the family may be expressed as:

Occurrence of internal phloem is a characteristic feature of the family. Vessels are in multiples of 4 or more cells; perforations are simple and the rays are uniseriate. Branched sclerenchymatous idioblasts frequently occur beneath the epidermis.

The family consists of about 600 species under 26 genera which occur in the tropical and subtropical regions. In India several species of Strychnos, Mitreola, Mitrasacme etc. are found in the plains as well as at lower elevations on the hills.

Loganiaceae is allied to Gentianaceae. Engler placed Loganiaceae in the suborder Gentianineae of his order Contortae with Gentianaceae, Apocynaceae and Asclepiadaceae. Rendle and Wettstein also included these 4 families in their Contortae, recognising the close relation between Loganiaceae and Gentianaceae.

Cronquist also considers these 2 families very close and includes these in his Gentianales where he includes Apocynaceae and Asclepiadaceae also. Hutchinson, however, considered Loganiaceae to be more allied to Oleaceae and placed Oleaceae in his Loganiales of the Lignosae while Gentianaceae was placed in Gentianales of the Herbaceae far removed from Loganiaceae.

Several plants of the family are important economically being the source of various alkaloids and are used medicinally.

Strychnine and brucine ane obtained from Strychnos nux-vomica Linn. Strychnos potatoram L. f. is the clearing nut tree the seeds of which purifies muddy water. Str. toxifera Schomb. gives the arrow-poison in S. America. Gelsemium sempervirens Linn, is also a medicinal plant. Fagraea fragrans Roxb., F. elliptica Roxb. and F. crenulata Maing. are good timber trees.

Family # 3. Buddlejaceae:

Buddlejaceae are shrubs or trees, rarely undershrub’s, very rarely herbs; glandular or stellate hairs often present or with lepidote scales. Leaves are simple, opposite or vermiculate, entire or coarsely dentate, connected by an intrapctiolar stipulary line. Inflorescence cymose, racemose or paniculate or capitate, or flowers solitary.

Calyx gamosepalous, 4-lobed; valvate. Corolla tubular with 4 lobes, imbricate. Stamens 4, epipetalous; filaments short or anthers sessile; anthers 2-locular, dehiscing longitudinally.

Carpels 2, united to form a superior 2-cellcd or very rarely 4-celled ovary; ovules many, on axile placentas; stigma capitate or 2-lobed. Fruit a capsule, drupe or berry; seeds often winged or produced at each end; endosperm scanty; embryo straight.

Floral formula:

K ₍₄₎ C ₍₄₎ A ₍₄₎ G ₍₂₎.

Stem anatomy shows the absence of intraxylary phloem. An integumentary tapetal layer is found and the endosperm is cellular. These characters separate Buddle­jaceae from Loganiaceae.

The family Buddlejaceae contains about 150 species under 6 genera, distributed in the tropical and temperate regions. Buddleja, the largest genus has over 100 species some of which are cultivated for beautiful fragrant flowers. There are several species of the genus in the lower ridges of the Himalayas and B. asiatica Lour, is found in the plains of India.

Buddlejaceae was included in Loganiaceae from which it was segregated as distinct family by Hutchinson who considered the 2 families to be close to each other. Hallier included Loganiaceae with Buddlejoideae as a subfamily in the Tubiflorae while both Takhtajan and Cronquist place Buddlejaceae in Scrophulariales. According to them the affinity of Buddlejaceae is closer to Srrophulariaceae than to Loganiaceae.

Family # 4. Gentianaceae:

Gentianaceae are annual or perennial herbs, often rhizomatos; branching often dichotomous; rarely floating aquatics. Leaves are simple, opposite and decussate, rarely alternate, exstipulate, 3-5-nerved. Inflorescence cymose, often dichasial.

Flowers are regular, bisexual, hypo­gynous, 4-5-merous, bracteate. Sepals 4-5, connate at base, imbricate, persistent. Corolla tubular, rotate or salver-shaped or funnel-shaped, 4-5-lobed, contorted or in duplicate valvate. Stamens as many as and alternate to Gorolla-lobes; anthers 2- celled, introrse, basi- or dorsifixed or sometimes versatile.

Ovary superior, bicarpellary, syncarpous, usually unilocular, with many ovules on 2 parietal placentas; ovules anatropous; style simple, stigma capitate or bilobed; glandular hypogynous disc is often present. Fruit a capsule with leathery valves. Seeds with fleshy perisperm and minute embryo.

In most herbs the branching is forked cymose. Some species of Gentiana (sec. Crawfurdia) are twiners and Nymphoides species are floating aquatic herbs. A few genera are saprophitic, e.g. Voyria, Leiphaimos, etc. Flowers of Hoppea are more or less zygomor­phic but regular in other genera.

Cotylanthera species are parasitic and Gentiana crassa Kurz is shrubby. Pitted glands secreting nectar are found at the base of petals in Swertia. Stamens have syngenesious anthers in Voyria and Leiphaimos. Multisporangiate stamens are often found due to the presence of sterile plates between anther lobes.

In Exacum the dehiscence of anthers is by apical pores. In the same genus the ovary is fal­sely 2-locular due to the intrusion of the placentas and meeting at the centre. Rarely the ovary is 4-5-locular due to the growth of more false septas. Enantiostyly, i.e. the style bent to one side, is found in Exacum.

In Canscora 1 or 2 stamens with longer filaments have fertile anthers while the rest have shorter filaments and sterile anthers and inser­ted at lower level, often almost obsolete. The fruit of Chironia is a berry.

Floral formula is represented as:

Vascular bundles are bicollateral in the subfamily Gentianoideae but collateral in the Menyanthoideae. The cells contain bitter principles, and stellate hairs are present in intercellular spaces. Cells of the pericycle are thin walled; vessels have simple per­forations and fibres are scanty.

The family comprises 80 genera and about 900 species, the largest genus Gentiana having about 400. The family is distributed more in the temperate region while quite a large number occur also in the tropics in various ecological situations. A few species of Gentiana occur in the artic zone and also in alpine tracts.

In India many species of Gentiana and Swertia are found in the Himalayas and hills of eastern India while Canscora diffusa R. Br., C. decussata R. & S., Exacurn tetragonum Roxb., Etythraea Roxburghii G. Don, Nymphoides cristata (Roxb.) O. Ktze.,etc. are common in the plains all over the country.

The family is divided into 2 subfamilies:

I. Gentianoideae:

Leaves opposite; corolla lobes twisted in bud; vascular bundles bi collateral having intraxylary phloem.

II. Menyanthoideae:

Leaves alternate; corolla induplicate-valvate vascular bundles collateral, lacking in internal phloem. The family is allied to Loganiaceae and to Melastomaceae in some respects.

Hutchin­son considers that Gentianaceae and Caiyophyllaceae having same type of inflorescence have close affinity with each other and that Gentianales originated from Caryo­phyllales. Hutchinson further raises the subfamily Menyanthoideae to the rank of a family, viz. Menyanthaceae and most subsequent authors support him in such treatment.

Gentianaceae includes a few economically important plants. Swertia chirayita a Hima­layan herb is a reputed medicinal plant. Gentiana lutea, G. campestris, G. punctata, G. Kurroo (Himalaya) are all medicinal plants. Canscora decussata R. & S. is used by the Indian vaids. Many species of Gentiana, particularly G. acaulis are cultivated in gardens for their beautiful blue flowers.

Family # 5. Menyanthaceae:

Treated as a distinct family it is characterised as:

Menyanthaceae are aquatic or marsh herbs. Leaves are simple or 3-foliolate, exstipulate, with a sheathing petiole. Inflorescence cymose or racemose or flowers clustered. Flowers are bisexual, actinomorphic, hypogynous. Sepals 5, free or united. Petals 5, united, lobes valvate or induplicate-valvate. Stamens 5, epipetalous, alternating with corolla lobes; anthers versatile, sagittate; hypogynous nectary usually present.

Ovary superior, bicarpellary, syncarpous, unilocular; ovules many on 2 parietal placentas; style simple with a bifid stigma. Fruit a capsule, with 2-4 valves or fleshy and indehiscent. Seeds few or many, often winged; endosperm copious; embryo minute.

The family contains about 33 species under 5 genera distributed in the tropical countries. Nymphoides cristata (Roxb.) O. Kuntze is very common in fresh water pools all over India in the plains. The vascular bundles do not have internal phloem as is found in Gentianaceae. A tapetal layer is found in the integuments and the endosperm is cellular.

Hutchinson who splitted Gentianaceae to Gentianaceae and Menyanthaceae included these 2 families in his Gentianales where no other family is included. Takhtajan places these 2 families in Gentianales where 9 other families are included by him. Cronquist, however, removes Menyanthaceae from Gentianales and places it in Scro­phulariales.

Family # 6. Apocynaceae:

Apocynaceae are trees or shrubs often twining, rarely undershrub’s, usually with milky latex. Leaves are simple, opposite or whorled, rarely alternate, exstipulate, entire. Inflorescence cymose, or flowers solitary. Flowers are bisexual, actinomorphic, hypogynous, bracteate or not.

Sepals 5, united at base, quincuncial, rarely sepals 4and imbricate; often with basal glands. Petals 5, united in a salver-shaped or funnel-shaped corolla; lobes contor­ted in bud; a hairy or scaly corona or various outgrowth present at the throat of corolla.

Stamens as many as petals and alternate with them, epipetalous; filaments short or almost absent; anthers introrse, often sagittate, free or connivent in a cone over the stigma and often adnate to it, base of anther often produced downward in the form of spines; pollens sometimes in tetrads; an entire, lobed or scaly disc is often pre­sent.

Carpels 2 forming a syncarpous ovary, or the ovaries united by styles and stigmas; ovaries superior or semi-inferior; 2-celled in the case of syncarpous ovary; or pair of unicellular ovaries; ovules many, aratropous, pendulous from a parietal placenta; style slender; stigma capitate or dumb-bell shaped.

Fruit a pair of follicles or berries or capsules or a single fruit in the case of syncarpous ovary. Seeds flat, winged or comose; endosperm copious or rarely absent; cotyledons large and thin.

Branched and un-branched latex tubes are present throughout the plant body. The vascular bundles are bi-collateral having intraxylary phloem. Spicular cells are found in the leaf-n esophyll.

Non-lignified fibre-like cells occurring in groups or in a ring form the pericycle. Wood parenchyma is apotracheal or sometimes paratracheal. Fibres are septate, with simple or bordered pits. In many twining species anomalous secondary thickening is observed.

The family contains about 300 genera and about 1400 species, occurring in the tropical regions with a few in temperate areas. It is well represented in India by about 85 species.

Most common are Alstonia scholaris R. Br., Holarrhena antidysenterica Wall., Carissa carandas Linn. Aganosma dichotoma K. Schura., Ervatania divaricata Burkill, Ichno- carpus frutescens R. Br., Wrightia coccinea Sims, Nerium indicum Mill., Rauvolfia serpentina (L.) Benth & Kurz. etc.

Alstonia attains large size; other trees are usually short. Ervatamia, Carissa, Kopsia, etc. are shrubs, Carissa being spiny. Aganosma, Vallaris, Beaumontia, Landolphia are exten­sive climbers.

Landolphia climbs by tendrils which are metamorphosed peduncles. Catharanthus, Vinca, etc. are undershrub’s or herbs. Adenium is a succulent xerophyte. Cerbera odollam Gaertn. a small tree with drupaceous fruits grows in the magrove forests south of Bangladesh.

Leaves are opposite in most genera; 3 in a whorl in Nerium, Rauvolfia etc., 3-7 in Alstonia, while in Cerbera leaves are alternate, and spiral and cfowded in Thevetia. Flowers bell-shaped in Allamanda, otherwise salver-shaped or funnel-shaped. Anthers are tailed in the subfamily Echitoideae but not so in Plumerioideae.

There is no corona or any such outgrowth within the corolla of Plumeria which has a semi-inferior ovary. Fruits of Melodinus and Carissa are berries, those of Thevetia, Cerbera, Rauvolfia, are drupes and in most genera they are follicles. Seeds are peltately attached in Carissa, Cerbera etc. Ruminate endosperm is often found in Ervatamia.

The floral formula is expressed as:

The family is subdivided into 2 subfamilies as noted below:

Sub f. I. Echitoideae—Corolla lobes twisted to the right; stamens closely adhe­rent to the stigma; anthers with distinct tails Nerium, Vallaris, etc.

Sub f. II. Plumieroideae—Corolla lobes twisted to the left; stamens more or less free from stigma; anthers not tailed. Plumeria, Catharanthus, etc. The family is closely allied to Asclepiadaceae and the two families are always included in the same order. It is related to Oleaceae and to Gentianaceae in some respects.

The family includes a few important medicinal plants, e.g, Rauwoljia serpentina (L.) Benth. ex. Kurz., R. lelraphylla Linn., Holarrhena antidysenterica Wall. etc. Wrightia tinctoria R. Br. yields a blue dye from the leaves.

The latex of Acokanthera is deadly poisonous and is used in Africa as arrowpoison. Many other species have poisonous properties, and the latex of Carpodinus lanceolatus Schum., Landolphia Kirki Dyer contains caoutchoc.

Alstonia scholaris R. Rr. is a good timber plant the bark of which is used medicinally. A few are grown in gardens for the showy flowers, viz, Nerium indicum Mill. Thevetia peruviana Scham., Plumeria rubra Linn., Catharanthus roseus G. Don., etc.

Family # 7. Asclepiadaceae:

Asclepiadaceae are erect or climbing shrubs or herbs, rarely short trees, with milky latex. Leaves are sim­ple, entire, exstipulate, usually opposite or decussate Inflorescence cymose, often umbellate. Flowers are bisexual, actinomorphic, hypogynous. Sepals 5, slightly united at the base, 5-partite. quincuncial. Corolla rotate or campanulate, 5-lobed, contorted or valvate in bud; often provided with appendages forming a corona.

Stamens 5; fila­ments connate in a hollow column enclosing the style; the anthers adnate to the stigma in a 5-angled disc-shaped gynostegium; the pollens united in 1 or 2 pollinia in each anther lobe (Subfam. Cynanchoideae) or remain in tetrads (Subfam. Periplocoideae) or grrnular; the pollinia usually united in pairs to a gland on the pentangular stigmatic disc and are covered by a membrane.

Carpels 2, free below and united by the styles and stigmas. Ovaries superior, with numerous anatropous ovules, pendulous from the ventral suture. Fruit a pair of follicles; seeds comose, with scanty cartilaginous endos­perm and a large embryo.

The corona in Asclepiadaceae may be. a true corona of elaboration of fleshy fila­ments of stamens, or it may be a faucal annulus of the corolla tube, or appendages of the anthers. A pair of pollinia consists of the contents of adjacent anther cavities of con­tiguous anthers.

Each pollinium has a translator arm, the translators with gland are formed between neighbouring anthers. The translator arm is often called retinaculum or connective and the gland the corpusculum. In .this family erect or climbing shrubs predominate. Calotropis often attains the size of a small tree. A few are xerophytes and are succulents, e.g. Stapelia where the leaves are modified to spines or reduced to scales.

Dischidia and some species of Hoya are epiphytes. In Dischidia one of a pair of leaves is often transformed into a pitcher where rain water and dust particles collect and are absorbed by the plant by means of a few adventitious roots that grow inside the pitcher.

There is not much variation in the structure of flowers in this family, which has 2 distinct types of pollens, i.e. granular tetrads and pollinia. The flowers of Ceropegia is jug-shaped and slightly zygomorphic. Secamone has 4-celled anthers.

Floral formula is represented as:

The family contains about 1800 species under about 250 genera in the tropical countries. In India Asclepiadaceae is well represented by about 330 species. Calotropis gigantea R. Br. and C. procera R. Br. are the Arka-puspa or Akanda common almost every-where in the plains.

Hemidesmus indicus R. Br., the Anantamool, is called the Indian Sarsaparila. Finlaysonia maritima Backer is a halophytic plant found to grow in Sundriban forests. Dischidia occurs in Assam and Chittagong. Hoya has several species in different forests in India. Pergularia daemia Chiov. is common in the plains.

The vascular anatomy shows the presence of intraxylary phloem. Latex tubes are present in almost all parts. In the erect plants vessels are usually small in dimensions but these are large in the climbers. Perforations are simple, sometimes ring porous and the intervascular pitting is alternate. Fibres are bordered 01 simple-pitted. Sunken stomata are found in most of the xerophytic plants.

The family is divided into 2 subfamilies based on pollen characters:

I. Subf. Periplocoideae: Pollen granular, in tetrads; filaments free.

II. Subf. Cynanchoideae: Pollen grains united in pollinia; filaments united in a tube, surrounding the gynoecium.

The subfamily Periplocoideae is raised by some workers to the rank of a distinct family, viz. Periplocaceae.

Asclepiadaceae is closely allied to Apocynaceae and the 2 families are placed side by side in the different systems of classifications of the Angiosparms.

Economically the family is not very important. Cryptoslegia grandiflora R. Br. yields a caoutchouc and is grown in some countries commercially. Gymnema lactiferum Linn, of Ceylon yields edible milky latex.

Hemidesmus indicus R. Br. is the Indian Sarsaparila and is also used in snake-bite and scorpion-bite. Many species are poisonous and the latex of Matelea species is used as arrow-poison. Gonolobus condurango Linn, yields the medicinal condurango bark.