Rubiaceae: Characters, Distribution and Types

In this article we will discuss about:- 1. Characters of Rubiaceae 2. Distribution of Rubiaceae 3. Economic Importance 4. Affinities 5. Important Types.

Characters of Rubiaceae:

Trees or herbs; leaves alternate or opposite; stipules interpetiolar or intrapetiolar, inflorescence cymose; flowers tetra or pentamerous, hermaphrodite, actinomorphic, epigynous, corolla, gamopetalous; stamens 4-5; epipetalous, introrse, dithecous; ovary inferior, bilocular with one or many ovules in each loculus; fruit capsule or berry.

A. Vegetative characters:

Habit:

Mostly shrubs (Gardenia, Ixora, Mussaenda, Hamelia); trees (Morinda, Adina) and a few herbs (Galium, Rubia).

Root:

Much branched tap root system.

Stem:

Erect, herbaceous or woody or twinning (Manettia), climbing by hooks (Uncaria), branched, cylindrical or angular, hairy or smooth.

Leaves:

Cauline, ramal, opposite or verticillate, simple, entire or toothed, stipulate, stipules bristle like (Pentas) and leafy (Galium, Rubia), stipules mostly interpetiolar or sometimes intrapetiolar; unicostate reticulate venation.

B. Floral characters:

Inflorescence:

Solitary (Gardenia) usually cymose or globose head (Adina), or panicled cyme; may be axillary (Coffea arabica) or terminal cyme (Mussaenda glabra).

Flower:

Actinomorphic, rarely zygomorphic (some what bilabiate as in Henriquezia), mostly hermaphrodite, rarely unisexual, epigynous, pedicellate or sessile (Greenia, Randia), bracteate or ebracteate, complete, tetra or pentamerous, cyclic, variously coloured.

Calyx:

Sepals 4 or 5, gamosepalous, superior, sometimes one sepal modified into coloured bract like structure (Mussaenda), valvate.

Corolla:

Petals 4 or 5, gamopetalous, lobed, generally funnel shaped (Asperula), tubular (Ixora), valvate to twisted or imbricate, superior.

Androecium:

Stamens 4 or 5, rarely many (Gardenia), epipetalous, alternipetalous, inserted near the mouth of corolla tube, stamens dithecous, introrse, dehiscing longitudinally, superior.

Gynoecium:

Bicarpellary, rarely polycarpellary, syncarpous, inferior rarely half inferior (Synaptanthera) or superior (Paganea), sometimes unilocular (Gardenia) with one to many anatropous ovules in each loculus, axile placentation (parietal placentation in Gardenia), style one sometimes bifid or multifid, stigma simple or bilobed.

Fruit:

Capsular (Anotis), berry (Mussaenda, Hamelia, Ixora).

Seed:

Endospermic, sometimes winged.

Pollination:

Entomophilous; ant pollination is well known.

Floral formula:

Distribution of Rubiaceae:

It is commonly known as Madder or Coffee family. It includes 6000 species and 500 genera. In India it is represented by 551 species. The members of this family are distributed in tropics, sub-tropics and temperate regions.

Economic Importance of Rubiaceae:

I. Medicinal plants:

Bark of Cinchona officinalis yields an alkaloid called Quinine which is the best remedy for malarial fever. The roots of Rubia cordifolia are also used as medicine.

II. Beverage plants:

The seeds of Coffea arabica, C. liberica and C. robusta are roasted and ground to give coffee powder.

III. Ornamental plants:

Rubia, Hamelia, Gardenia, Ixora, Mussaenda are cultivated in gardens for their beautiful flowers.

Affinities of Rubiaceae:

The family is closely related to Adoxaceae and Caprifoliaceae in the presence of inferior ovary, actinomorphic and hermaphrodite flowers, type of inflorescence, reduction in the number of carpels and ovules. The Rubiaceae also resembles the Loganiaceae in well developed stipules, glandular trichomes, nuclear endosperm. Rubiaceae differ from Loganiaceae in possessing inferior ovary.

Bessey traced the origin of Rubiales from the Umbellales which in turn originated from the Rosales. The Rubiales resemble the Umbellales in aggregation of flowers, reduction in the number of calyx and corolla lobes, stamens and carpels; in both epigynous flowers with nectar secretory disc are present. This suggests a close taxonomic relationship among the Rubiales and the Umbellales.

Primitive characters:

1. Plants mostly trees and shrubs.

2. Leaves simple and stipulate.

3. Flowers mostly hermaphrodite and actinomorphic.

4. Stamens polyandrous.

5. Ovules anatropous and many in some genera.

6. Seeds endospermic.

Advanced characters:

1. A few plants are herbs (Rubia, Galium).

2. Leaves opposite or whorled.

3. Flowers epigynous and rarely unisexual, zygomorphic.

4. Calyx and corolla fused.

5. Stamens epipetalous.

6. Carpel number reduced to two.

7. Fruit simple.

Common plant of the family:

1. Coffea arabica (Coffee):

An evergreen shrub, cultivated for seeds.

2. Cinchona officinalis (Quinine):

Tree cultivated for medicinal importance.

3. Hamelia:

A large evergreen shrub with reduced flowers.

4. Rubia:

A common climbing herb.

5. Gardenia:

A resinous shrub or tree.

6. Ixora:

Evergreen shrub with showy flowers. Many species are cultivated in gardens as ornamentals.

7. Mussaenda:

A shrub, very conspicuous during flowering.

Division of the family and chief genera:

Verdcourt (1958) divided the family into three sub-families:

Sub-family 1. Cinchonoideae:

Seeds endospermic, trees, shrubs rarely herbs, ovules indefinite in each loculus on axile placentation.

It includes eleven tribes viz., Nucleaceae, Cinchoneae, Rendeletieae, Mussaendeae, Catesbaceae, Gardenieae, Ixoreae, Alberteae, Vanguerieae, Retiniphylleae, Chiococceae.

Sub-family 2. Rubioideae:

Trees, shrubs or herbs, ovary one to many locular, ovule single or many, erect or pendulous. It includes 18 tribes. The chief genera are Rubia, Hamelia, Morinda.

Sub-family 3. Guettardoideae:

Seeds non-endospermic, or endosperm very little trees or shrubs; aestivation imbricate or valvate; ovary two to many locular with one pendulous ovule per loculus.

Important Types of Rubiaceae:

1. Hamelia patens:

Habit:

Evergreen perennial shrub.

Root:

Branched tap root.

Stem:

Erect, woody, cylindrical, solid, brownish-green with nodes and internodes, branching simple, hairy.

Leaves:

Whorled-3 or more leaves at each node, simple, petiolate, lanceolate, entire, acute, smooth, unicostate reticulate.

Inflorescence:

Multiparous cyme; each branch helicoid.

Flower:

Ebracteate, pedicellate, complete, hermaphrodite, pentamerous, actinomorphic, epigynous, reddish.

Calyx:

Sepals 5, gamosepalous, adnate to ovary, greenish brown in colour, superior, valvate aestivation, persistent.

Corolla:

Petals 5, gamopetalous, tubular, dark red, twisted.

Androecium:

Stamens 5, epipetalous, alternipetalous, linear, dithecous, anthers very long, filament short, basifixed dehiscing by longitudinal slit, introrse.

Gynoecium:

Pentacarpellary, syncarpous, pentalocular, axile placentation, ovary inferior, many ovules per loculus, style distinct, stigma single, terminal.

Fruit:

Capsular.

Floral formula:

2. Ixora parviflora:

Habit:

Evergreen shrub.

Root:

Branched tap root system.

Stem:

Erect, woody, cylindrical, solid, branched, green.

Leaves:

Opposite, decussate, sessile, Simple, stipulate, simple interpetiolar, cuspidate, oblong, entire, acute, unicostate reticulate.

Inflorescence:

Terminal cyme.

Flower:

Bracteate, pedicellate, complete, hermaphrodite, actinomorphic, tetramerous, epigynous, white or pink.

Calyx:

Sepals 4, gamosepalous, calyx tubular, persistent, valvate.

Corolla:

Petals 4, gamopetalous, tubular, twisted in bud, white or pink.

Androecium:

Stamens 4, polyandrous, epipetalous, on the mouth of corolla tube, alternipetalous, filament short, anthers dithecous, introrse.

Gynoecium:

Bicarpellary, syncarpous, bilocular, ovary inferior, axile placentation, one ovule in each loculus, style simple, filiform, hairy; stigma slender, fusiform, bifid.

Floral formula:

3. Mussaenda (Fig. 67.1):

Habit:

An ornamental, perennial, evergreen, shrub.

Root:

Branched, tap root.

Stem:

Herbaceous but woody in the lower portions, erect, cylindrical, branched, differentiating into nodes and internodes; internodes are swollen, hairy and green.

Leaf:

Ramal and cauline, simple, opposite decussate, sub-sessile, interpetiolar stipules are present, lanceolate, entire, acute, unicostate reticulate.

Inflorescence:

Dichasial cyme.

Flower:

Bracteate, pedicellate, complete, hermaphrodite, actinomorphic but mature and older flowers are zygomorphic, pentamerous, epigynous, whitish yellow.

Calyx:

Sepals 5, polysepalous or sometimes gamosepalous; 4 sepals are smaller and 5th one is modified into a yellow leafy bract in zygomorphic flowers; all sepals are of same shape, size and colour in actinomorphic flowers; persistent, valvate, green.

Corolla:

Petals 5, gamopetalous, corolla tube is elongated and funnel shaped, valvate or rarely imbricate, yellow; coronary structures are present in the form of silky hairs.

Androecium:

Stamens 5, alternipetalous, polyandrous, epipetalous, dithecous, basifixed or dorsifixed introrse.

Gynoecium:

Bicarpellary, syncarpous, inferior, bilocular, many ovules, axile placentation; style long with two stigmatic lobes.

Fruit:

A berry.

Seed:

Many, small, endospermic.