Classification of Centrospermae: 8 Families

In this article we will discuss about the classification of Centrospermae. According to Engler, Centrospermae consists of eight families:- 1. Chenopodiaceae 2. Amaranthaceae 3. Nyctaginaceae 4. Phytolaccaceae 5. Aizoaceae 6. Portulaccaceae 7. Basellaceae 8. Caryophyllaceae.

Family # 1. Chenopodiaceae:

Chenopodiaceae are annual or perennial herbs or shrubs, very rarely trees, often with swollen nodes, glabrous or “mealy” (covered with small hairs-with a large terminal cell that readily falls off). Leaves of Chenopodiaceae is simple, exstipulate, often thick and fleshy, glabrous or “mealy”, alternate or rarely opposite, entire or variously lobed.

Inflorescence is a mixed panicle, small cymes arranged in racemes or spikes or often a thyrsus.

Flowers of Chenopodiaceae is small and in­conspicuous, bisexual or unisexual, usually regular, bracteate and bracteolate or without bracts and bracteoles. Perianth of 5 or less segments in one whorl, sepaloid, persistent, free or connate.

Stamens of Chenopodiaceae is as many as perianth segments and opposite to them; anthers 2-celled; pollens spherical and with numerous spores; filaments often connate at base; often stamens less rarely a whorl of staminodes also present.

Ovary superior, rarely inferior, of 3-2 carpels, syncarpous, unilocular; ovule one, basal; style usually one, rarely 2 or 3 and free; stigma capitate or 2-3-lobed. Fruit a nut or a utricle usually enclosed by the persistent perianth, rarely dehiscing transversely. Seeds with powdery perisperm and curved or coiled embryo.

Floral formula of the usual type of flowers is:

but deviation from the type occurs. In Halocnemum, Alexandra and Crorispermum flowers are irregular, the perianth segments being of different shape and size. Artiplex, Spinacea, Sarcobatus, Garrya etc. have unisexual flowers.

The female flower of Artiplex have no perianth but have 2 bracteoles which enlarge and completely cover the fruit. Some authors consider these as 2 perianth segments and not bracteoles. In male flowers of Sarcobatus maximiliani Nees perianth is wanting and a single perianth segment is present in Monolepis where there is only one stamen.

Some plants of Chenopodiaceae are succulents and the jointed stems are almost leafless. In Salicornia the leaves are very small, sheath-like and connate. These are often terete e.g. Suaeda, linear-lanceolate in Kochia. Kochia indica Linn, is a tall erect annual up to 2 mtr. high, Chenopodium album Linn, also is tall and erect while Haloxylon ammodendron Bunge of the Central Asian steppes is a small tree attaining 6-7 mtrs. in height.

Anomalous secondary growth is a characteristic feature in the family. Secondary cambium develops in the pericycle or rarely in phloem and due to its activity concentric zones of scattered collateral vascular bundles are formed.

The Chenopodiaceae family consists of about 105 genera and 1,500 species, distributed almost all over the globe especially on saline tracts. Most of them are halophytes or xerophytes. The mealy hairs of many species have the capacity of storing water. In Artiplex the dense coat of hairs store enough water in the rains to prevent desiccation in the prolonged dry season.

In India a few species are met with in the Sundriban forests, viz. Suaeda maritima Dumort, Arthrocnemum indicum Moq., Salicornia brachiata Roxb. etc. Chenopodium album Linn, and Ch. ambrosioides Linn, are common almost all over the country and the former is often cultivated.

Suaeda fruticosa (L) Forsk. Atriplex crassifolia G. A. Mey, Salicornia herbacea Linn, grow in saline and arid regions of N. India. Acroglochin cheno- podioides Schrad. and Chenopodium botrys Linn, occur in the Himalayas above 2000 mtrs.

Of those species of the family economically important Beta vulgaris Linn, the Beet root is cultivated on a large scale in temperate countries for manufacture of sugar. It is also cultivated in other countries for the tuber-like taproot which is used as vege­table or in salad.

Chenopodium anthelminticum Linn, yields “Oil of Chenopod” having medicinal value. Ch.. quino Linn, of the hills of Peru produces starchy seeds used as a substitute of rice. The tender parts of Chenopodium album Linn., Spinacea oleraceae Linn, and a few others are used as pot-herbs.

The Palang or Palki is a variety of Beta vulgaris Linn. Kochia scoparia Schr. and K. trichophylla Voss. are cultivated in gardens as orna­mental plants. Among other families of the order Centrospermae this family is closely allied to Amaranthaceae and Phytolaccaceae.

Family # 2. Amaranthaceae:

Amaranthaceae are predominantly annual or perennial herbs, rarely shrubs, either erect or scandent. Leaves of Amaranthaceae is simple, exstipulate, alternate or opposite, usually entire. Inflorescence is a dense simple or branched spike or raceme, sometimes a dichasial cluster.

Flowers of Amaranthaceae is small, regular, hermaphrodite or rarely unisexual or polygamous, with a scarious bract and a pair of persistent bracteoles; the anatomy of the bracteoles show that these are nothing but the metamorphosed lateral flowers of a biparous cyme.

Perianth of single whorl, segments 3-5, free or connate at base, imbricate, persistent, dry and membranous, scarious or sepaline, often coloured. Stamens usually 5, opposite to perianth segments, free or united partially or completely into a tube, often with fringed or lobed outgrowths between 2 filaments; anthers 4-celled or 2-celled, dehiscing by vertical slits; often staminodes are present.

Ovary of 2-3 carpels, syncarpous, unilocular, superior; ovule solitary, basal, campylotropous, rarely ovules several; styles 1-3; stigmas various.

Fruit a nutlet or utricle, rarely a capsule dehiscing irregularly or transversely by a lid, enclosed by persistent perianth and bracteoles; very rarely the fruit is a drupe or a berry. Seed with a shining or rough testa, small and lenticular, with a horse-shoe shaped or annular embryo surrounding copious mealy endosperm.

Deeringia amaranthoides (Lamk.) Merrill is a climbing shrub with long branches han­ging from the supporting trees. Branching is often trichotomous, e.g. Pupalia, Psilo- trichum.

Leaves of Amaranthaceae are often coloured or mottled. Spines rarely present in leaf-axils; bracts and bracteoles often spine-scent at the tip. Sometimes the lateral flowers in a cluster are abortive and are replaced by spiny outgrowths. These persist in fruit and help in dis­tribution by animals, e.g. Achyranthes.

Anomalous secondary growth occurs similar to Chenopodiaceae in the formation of collateral vascular bundles from cambium in the pericycle. The fascicular cambium is functionless in the scattered vascular bundles.

The Amaranthaceae family consists of about 800 species in 72 genera distributed mainly in tropical countries of the world.

It is represented in India by several species of Amaranthus, Achyranthus aspera Linn. Aerva lanata Juss, Pupalia atropurpurea Moq. etc. Celosia cristata Linn, the Cock’s Comb and Gomphrena globosa Linn, the Globe Amaranth are garden favourites, and Alternanthera versicolor Regel is planted as a border plant in flowerbeds.

Achyranthes aspera Linn, is reputed to have medicinal value and much used by Indian Vaidyas. Amaranthus tricolor Linn, and its varieties are much used as pot herbs and the tall herb A. caudatus Linn, is also used in the same manner and the seeds are eaten as substitute of rice.

Amaranthaceae is allied to the other families of Centrospermae and particularly to Chenopodiaceae from which it differs in having flowers very densely arranged in the inflorescence, bracts and bracteoles scarious, perianth membranous and shining and filaments of stamens usually connate.

Family # 3. Nyctaginaceae:

Nyctaginaceae are perennial herbs or shrubs often scan-dent, rarely attaining great size. Leaves of Nyctaginaceae is simple, exstipulate, opposite or rarely alternate, often one of the opposite pair smaller than the other. Inflorescence is usually a panicle of biparous cymes often becoming uniparous in the upper part due to suppression of branches on one side; bracts usually forming an involucre.

Flowers of Nyctaginaceae  is hermaphrodite, rarely unisexual, actinomorphic, with one whorl of perianth. Perianth segments 4-5, usually petaloid, connate, infundibuliform or tubular; lobes imbricate or contorted; the base of the perianth tube is persistent while the upper part withers and gets detached.

Stamens of Nyctaginaceae is 2-20, more often 5-8; filaments unequal. Ovary monocarpellary, unilocular, superior, with one basal campylotropous ovule; style usually long. Fruit an achene enclosed by the persistent perianth-base— the anthocarp. Seed with a thin testa, with perisperm and curved embryo; cotyledons broad, foliacious and unequal.

Bougainvillea are lianes; here 3 flowers are found in a cluster each subtended by a coloured tract of the involucre, the terminal flower is wanting.

Pisonia spp. are shrubs or trees, the bracts of the involucre here are reduced to small teeth; the seeds have straight embryo. In Mirabilis the 5-partite involucre is sepaloid and subtends one or more flowers. In Neea the fruit is a pseudo-drupe, the persistent portion of the perianth becoming fleshy.

Abnormal secondary growth in the stem is also met with in this family and the vascular bundles are scattered. Calcium oxalate crystals are found in the cells in almost all parts of the plants. The family contains about 30 genera and about 300 species confined to the warmer parts of the world the majority being tropical American.

Only a few are economically important. Neea theifera Oerst. of Brazil is used as a substitute of tea. Boerhaavia repens Linn, the “Punarnaba” of the Indian Kabirajas is reputed to have medicinal properties. Mirabilis jalapa Linn, the Four-o-clock plant and Bongainvillea spectabilis Willd. are much cultivated in gardens as ornamental plants.

Nyctaginaceae is closely related to Phytolaccaceae from which it is supposed to have been derived. It closely resembles Polygonaceae from which it is readily distinguished by the involucre of bracts, unilocular ovary and the anthocarp of the fruit.

Hutchinson removes Nyctaginaceae from Centrospermae and assigns it a position after Thyme- leaceceae in Thymeleales under Lignosae but this treatment has not been approved by other workers.

Family # 4. Phytolaccaceae:

Phytolaccaceae are mostly herbs or shrubs, often climbing rarely trees. Leaves of Phytolaccaceae are simple, alternate, exstipulate or with minute stipules. Inflorescence is a raceme or spike, usually terminal but often appearing axillary due to the vigorous growth of a branch from the base of the inflorescence; rarely the inflorescence is cymose.

Flowers of Phytolaccaceae is small, bisexual or rarely unisexual, regular, with one whorl of perianth. Perianth segments 4-5, connate or free, imbricate, sepaline or coloured. Stamens as many as perianth segments and opposite or alternate to them, filaments free or connate near base; often stamens more and in 2 whorls, rarely only 3; sometimes chorisis or splitting of stamens occurs and the number is much increased.

Carpels one or several, free or syncarpous; ovary superior, uni- or multi-locular, with one basal ovule in each cell; styles free. Fruit various, a nut or utricle, capsule or berry or drupe or often a schizocarp; seed with a curved peripheral embryo surrounding the powdery perisperm.

The flowers of Agdestis are epigynous. In Stegnosperma there is a whorl of petals above the whorl of sepals. These petals are nothing but metamorphosed stamens. Anomalous secondary growth occurs in some genera.

The Phytolaccaceae family with about 22 genera and 120 species is distributed mainly in the tropical and temperate countries of America and Africa. Rivina humiles Linn, a tall herb is an exotic weed growing in different parts of India. No species of this family is economically important except Phytolacca decandra Linn, the red berries of which are used for colouring wine.

Phytolaccaceae is closely related to the other families of Centrospermae and is considered by most authors to be most primitive among them and the rest of the families having originated from Phytolaccaceae. Pollen character and apocarpous pistil in some species of this family brings it close to the families in Ranales from which group the order Centrospermae might have originated.

Family # 5. Aizoaceae (Ficoideae):

Aizoaceae are annual or perennial herbs or under-shrubs, usually succulent. Leaves of Aizoaceae is simple, alternate or opposite, stipulate or not. Inflorescence cymose, or flowers solitary. Flowers of Aizoaceae is regular, bisexual, small or often large and showy. Sepals 4—8, more or. less united below, imbricate or valvate. Petals numerous or rarely absent.

Stamens of Aizoaceae many, filaments often connate. Ovary superior or inferior, 1-many chambered; ovules many in each chamber, axile or parietal; stigma 1-many. Fruit capsule, berry or nut. Seeds many; embryo curved, surrounding a mealy endosperm.

Some plants have succulent roots or caudices. Large watery cells rich in sugar cover the xerophytic plants. Calcium oxalate crystals are often present in epidermal cells. In some plants, e.g. Lithos species the leaves are somewhat hemispheric in shape and look like pebbles. These grow in rocky areas and resemble small stones scattered on the rocks. In some cases only one pair of leaves appear in a year.

The petals are staminodial in origin. The capsule are often hygroscopic the valves opening when wetted.

In Mesembryanthemum the ovary behaves peculiarly. The ovules are borne on axile placentas at first but subsequently the placentation becomes parietal.

Aizoaceae is a large family containing over 2,000 species, majority of which are found on the sandy tracts of S. Africa and a few in Europe, America, S. E. Asia and the South Seas. Common Indian species are: Trianthema portulacastrum Linn., Mollugo spergula Linn., Sesuoium portulacastrum Linn., etc.

The Aizoaceae family is closely related to Phytolaccaceae, Portulacaceae, Chenopodiaceae and Caryophyllacae, and is considered to have .been derived from Phytolaccaceae.

Many species of Aizoaceae are cultivated as ornamental plants, otherwise the family is of little economic importance. Tetragonia expansa Murr. — the New Zealand spinach is cultivated as potherb. Trianthema portulacastrum is also used as a potherb and is said to have medicinal value.

Family # 6. Portulaccaceae:

Portulaccaceae are succulent herbs or under-shrubs; calcium oxalate crystals present in the cells. Leaves of Portulaccaceae are simple, opposite or alternate, usually stipulate; stipules scarious or brisde-like, often stipules absent (Claytonia). Flowers of Portulaccaceae may be solitary but usually in racemose or cymose inflorescence, regular and hermaphrodite, hypogynous or slightly perigynous, with 2 whorls of perianth.

Sepals 2, anteroposterior, imbricate. Petals 4-6, rarely 2 or 3, disdnct or connate below. Stamens as many as petals and adnate to them at base, rarely stamens 3, sometimes double the number of petals as a result of splitting; anthers 2-celled, introrse, dehiscing longitudinally.

Carpels 2-5, syncarpous; ovary superior or semi-inferior, unilocular; ovules 2-co on free central placenta, campylotropous; funicle long and slender; styles 2-5. Fruit a capsule, dehiscing circumscissilely or by 2-5 apical valves; rarely fruit is a nut. Seed compressed, with a much curved embryo surrounding a mealy perisperm.

There is difference of opinion as regards the morphology of the perianth. According to some authors the perianth is uniseriate and the outer whorl is nothing but an in­volucre of bracts and not calyx and the apparent corolla is a perigone composed of sepals. Pax & Hoffmann and Warming are among others who are the supporters of this view.

Floral formula of a typical flower may be shown as:

The Portulaccaceae family comprises 19 genera and 500 species found in tropical and temperate countries but more in America and S. Africa. Portulaca oleracea Linn, and P. quadrifolia Linn, are common weeds all over India in the plains.

The former is often used as a pot herb. P. grandiflora Linn, is much cultivated in gardens for the showy flowers. Species of Talinum and Calandrina are also cultivated as ornamental plants. No other species is of any economic importance.

The family is allied to the other families of Centrospermae but more so to Baselaceae. It is allied to Caryophyllaceae and according to Pax and Hoffmann was derived from this family. Rendle as well as Cronquist considers that Portulacaceae like all other families of the order originated from Phytolaccaceae.

Family # 7. Basellaceae:

Annual or perennial herbaceous twiners. Leaves simple, alternate, entire, exstipulate, usually fleshy. Inflorescence is a spike or panicle, bracts and bracteoles present, often united to the base of the calyx. Flowers small, regular, bisexual. Perianth of one whorl of 5 free or united sepals, persistent; sepals or calyx lobes imbricate. Corolla absent.

Stamens 5, opposite to and inserted at the base of the sepals, free from each other; anthers short, 2-celled; cells parallel, dehiscing longitudinally. Carpels 3, syn­carpous, forming a unilocular superior ovary; ovule solitary, basal, campylotropous; style with tripartite stigma. Fruit a drupe, enclosed by the persistent often fleshy calyx; seed with a membranous testa and copious endosperm; embryo annular or spirally rolled.

This is a small family of 5 genera and 22 species confined to Tropical America and West Indies while Basella rubra Linn, and B. alba Linn, are cultivated as spinach in almost all tropical countries. Boussingultia is also cultivated in warm countries as an or­namental plant. The tuberous root of Ullucus tuberosus is consumed in its native country as a substitute for potato.

The family is related to the other members of the order Centrospermae having a curved embryo. In the old system of Bentham and Hooker it was included under Chenopodiaceae, later recognised as a distinct family closely related to Portulacaceae originating either from Caryopkyllaceae or from Phytolaccaceae.

Hutchinson, however, places Baseliaceae under his Chenopodiales while Portulacaceae is included in his Caryophyllales.

Family # 8. Caryophyllaceae:

Generally herbaceous plants or undershrub’s; branching is of biparous cymose type; nodes often swollen. Leaves simple, opposite and decussate, rarely alternate; sti­pules often present, scarious or membranous; usually one leaf of a pair develops earlier and has a more vigorous bud in the axil giving rise to a branch while the axillary bud of the other leaf does not develop into a branch; the close scale-like leaves of Pycnophyllum gives the plant a “Lycopodium” — like appearance.

Inflorescence is generally a biparous cyme the ultimate branches of which pass into scorpioid cymes; flowers are rarely soli­tary (Githago); bracts present subtending the branches of the inflorescence.

Flowers actinomorphic, hermaphrodite or unisexual by reduction, hypogynous or perigynous, 5-merous or 4-merous. Perianth in 2 whorls with distinct calyx and corolla, rarely corolla absent. Sepals persistent, free or connate, imbricate, often scarious. Petals free often clawed, valvate; the receptacle between corolla and androccium is often elongated.

Stamens in 2 whorls, 4-5 in each whorl, often fewer; staminodes sometimes present; anthers 2-celled, dehiscing longitudinally; disc annular or a whorl of glands, or often elongated in the form of a gynophore; nectaries present at the base of outer stamens or concealed at the base of calyx tube.

Carpels 2-5, united to form a syncarpous superior ovary; ovary often stipitate, unilocular or multilocular below; styles free or united below; ovules curved, 1-many on basal or central placenta. The fruit is a nut or achene, or capsule opening by apical valves or teeth as many as or double the number of carpels; rarely the fruit is a berry; seed with a curved embryo and mealy endosperm; rarely embryo is straight.

Floral formula of a typical flower is:

where there are 2 whorls of perianth, 2 whorls of stamens and the pistil, and 5 members in each whorl; instead of 5 there may be 4 members in each whorl, i.e. flowers may be pentamerous as in Spergula or Cerastium while in Sagina flowers are usually tetramerous. In Sagina apetala petals are absent or minute. In Lyallia petals are absent and stamens only 3.

In Drymaria, Polycarpon and Polycarpaea stamens are in one whorl, 5 or less. Sepals are free in the subfamily Alsinoideae but united in a tube in Caryophylloideae.

In this sub­family usually a corona is present. In Pteranthus the lateral flowers of a cluster of 3 are more or less abortive. Fruit is generally capsular but a nut in Paronychia, Herniaria, etc. and a berry in Cucubalus. Embryo is curved in all the genera but straight in Dianthus.

Where there are 2 whorls of stamens present obdiplostemonous condition is noticed. But this obdiplostemony is not true but apparent as has been proved by the study of floral anatomy. It is the result of pushing out of the inner stamens towards outside. Anomalous secondary growth occurs in a few genera of this family in the formation of more than one ring of vascular bundles.

The nature of stomata is very characteristic in this family. Each stoma has two subsidiary cells with transverse common wall, i.e. the common wall is at right angles to the guard cell. This type of stomata is the dia- cyclic type, also known as the Caryophyllaceous type.

The family consists of about 70 genera and about 1,750 species and are found to grow in almost all parts of the world but more in the Mediterranean region where there are several endermic genera. In India there are several species in the plains as well as in the hills.

Polycarpon loefiingiae Benth. & Hook, f., Stellaria media Linn., Saponaria vaccaria Linn. Polycarpaea corymbosa Lamk. are quite common in the plains while Spergula aroensis Linn., Drymaria diandra Bl. etc. in the hills. Several species of Arenaria occur in the Himalayas and a few in the alpine region which form a dense cushion. Lyallir is found above 3000 mtr. altitude.

Most plants of this family are of no economic importance except a few species of Saponaria which contain saponin in the roots. Some genera have beautiful flowers and are cultivated as season plants, e.g. Dianthus caryophyllus Linn.—the Carnation, D. chinensis Linn., D. barbatus Linn, and D. plumarius are the Pinks. Gypsopkila paniculata Linn, and G. elegans Linn, are also cultivated.

The family is related to the other families of the order Centrospermae all having curved embryo and perisperm in the seeds. Eichler considered that Caryophyllaceae originated from Phytolaccaceae and this view is supported by Pax, Wettstein and Rendle.

Wemham expressed the opinion that this family was derived from a Ranalian stock and most authors agree to this view. Hutchinson splits this family into Caryophyllaceae and Illecebraceae and places the latter with Polygonaceae in Polygonales but this treatment has not met with the approval of others.

The family is subdivided by Pax into 2 tribes and 8 sub-tribes as shown below:

I. Alsinoideae:

Flowers polysepalous, often perigynous.

(a) Fruit capsule:

1. Alsineae: Styles free to the base, leaves exstipulate. Stellaria, Cerastium Sagina, Arenaria, etc.

2. Sperguleae: Styles free to the base, leaves stipulate, Spergula, Spergularia etc.

3. Polycarpeae: Style united near base, Drymaria, Polycarpon, etc.

(b) Fruit achene or nut:

4. Pornychieae: Flowers all alike, leaves stipulate Corrigiola, Pornychia, Illecebrum, Hermiaria, etc.

5. Sclerantheae: Flowers all alike, leaves exstipulate Scleranthus, etc.

6. Pterantheae: Flowers in clusters of 3, the 2 laterals ± abortive, Pteranthus.

II. Caryophylloideae (Silenoideae):

Flowers gamosepalous, hypogynous.

1. Lychnideae: Calyx with commisural ribs, Silene, Lychnis, etc.

2. Caryophylleae (Diantheae): Calyx without commisural ribs, Gypsophila, Dianthus, etc..