Lamiaceae: Characters, Distribution and Types

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

Characters of Lamiaceae:

Sweet aromatic smell due to essential oils present in sessile glandular hairs; stem rectangular in cross section, leaves opposite decussate rarely alternate, simple, exstipulate with hairs; inflorescence verticillaster; flowers zygomorphic, hermaphrodite, hypogynous, bracteate; calyx gamosepalous, persistent; corolla bilabiate; stamens 4 epipetalous, didynamous; gynoecium 2 four celled by false septum, syncarpous, axile placentation, gynobasic style, seated on lobed disc; fruit schizocarpic carcerulus.

A. Vegetative characters:

Habit:

Plants are mostly aromatic herbs or shrubs (Leonotis, Pogostemon). Tree habit is found in the Brazilian genus Hyptis and climbing habit in American species of Scutellaria.

Root:

Tap, branched, rarely adventitious (Mentha).

Stem:

Aerial, herbaceous, rarely woody, erect or prostrate, quadrangular, hairy, branched, solid or hollow, sometimes underground suckers (Mentha).

Leaves:

Opposite decussate, rarely whorled, simple, petiolate or sessile, exstipulate, hairy with aromatic smell, entire, pinnatifid (Perovskia), unicostate reticulate venation.

B. Floral characters:

Inflorescence:

Very commonly verticillaster consisting of a pair of condensed dichasial cymes at each node; often the verticillasters are grouped together in a thyrsus form; rarely solitary (Scutellaria).

Flower:

Pedicellate or sessile, bracteate, complete, zygomorphic rarely actinomorphic (Mentha, Elsholtzia), hermaphrodite, rarely unisexual (Nepeta, Thymus), pentamerous hypogynous.

Calyx:

Sepals 5, gamosepalous, bilabiate (Salvia, Thymus) campanulate (Teucrium), persistent, valvate or imbricate aestivation. When a bilabiate calyx is present the arrangement of the sepals may be (1/4) as in Ocimum or (2/3) as in Calamintha.

Corolla:

The corolla possesses a tubular base which widens towards the mouth. Petals generally 5, gamopetalous and the five teeth are sub-equal and mostly bilabiate. In Mentha a four lobed corolla arises due to the fusion of two upper teeth. When a distinct bilabiate condition is found the arrangement of the petals may be gamopetalous 2/3 i.e. two petals in the posterior upper lip and three in the anterior lower lip (Salvia, Nepeta, Leucas etc.).

In Ocimum, Coleus, Plectranthus etc. the petals arrangement is gamopetalous 4/1 i.e. four petals in the posterior upper lip and only one petal in the anterior lower lip. In extreme cases the arrangement may be gamopetalous 0/5 i.e. all the five petals forming the lower lip so that the corolla becomes one lipped. Aestivation in the petals is valvate or imbricate.

Androecium:

Typically only 4 stamens, didynamous (2+2) and posterior stamen is reduced or represented by a staminode; in Calamintha only two perfect stamens are found, two are imperfect and the fifth reduced. In Salvia only two stamens on the anterior side are found; they are characterised by peculiarly long connectives which help in insect pollination stamens generally introrse and dithecous.

Gynoecium:

Bicarpellary, syncarpous, superior, situated on hypogynous honey secreting disc; bilocular becomes tetralocular by the formation of false septum; axile placentation, one ovule in each loculus; style gynobasic (arising from the base of the ovary), stigma bilobed. The gynoecium character is thus uniform without any variation.

Fruit:

Usually schizocarpic carcerulus or achenes or nutlets rarely drupaceous.

Seed:

Non-endospermic.

Pollination mechanism in the Lamiaceae:

According to Delpino there are five important characters of the flower affecting the pollination mechanism viz.:

(a) The horizontal position of the axis of the flower;

(b) Division of the corolla into an upper and a lower lip;

(c) Position of stamens and stigma below the upper lip which shelters them;

(d) Position of the nectary at the base of the flower below the lower lip whose anterior part forms a platform for insects; and

(e) Well marked dichogamy.

Muller, who is an authority on the pollination mechanism has remarked in this connection that out of the above the first three are generally true but not universal; the fourth is almost universal but dichogamy is not so complete so as to prevent self pollination.

The types of insects visiting these flowers have a remarkable correspondence with the length of the corolla tube. Those with short tubes are pollinated by flies; slightly longer tubed flowers, e.g. Thymus or Origanum are pollinated by bees; Salvia, Lamium, Teucrium with still longer tubes are pollinated by bees as well as other longer tongued insects.

Floral- formula:

Distribution of Lamiaceae:

It is commonly called Mint family. The family includes 260 genera and 3200 species of world wide distribution. In India it is represented by 400 species.

Economic Importance of Lamiaceae:

1. Food:

Tubers of Stachys sieboldi are edible. Leaves of Mentha viridis, Ocimum basilicum, Melissa officinalis etc. are used as condiments.

2. Medicinal:

Many plants of this family are used in medicines. Ajuga bracteosa, Leucas cephalotes are used in fever. Mentha piperata and Thymus serphyllum give Menthol and Thymol respectively, which are extensively used in medicines. Leaves of Ocimum kilimandus charicum give camphor.

Ocimum sanctum and other species of Ocimum are used in various ailments.

3. Ornamental:

Several species of Salvia, Coleus, Ajuga, Leonotis, Dracocephalum, Thymus, Lavandula etc. are cultivated in gardens for ornamental purposes.

4. Perfumes:

Aromatic oil is extracted from Thymus, Lavandula (Lavender oil), Rosmarinus (Rosemary oil), Calamintha, Pogostemon etc.

5. Dye:

Fruits of Lycopus europaeus yield red dye.

Primitive characters:

1. Some members are perennial shrubs.

2. Leaves simple.

3. Flowers hermaphrodite, hypogynous, coloured and scented.

4. Pollination by insects.

Advanced characters:

1. Plants mostly herbaceous.

2. Leaves exstipulate, opposite or whorled.

3. Flowers in distinct inflorescence.

4. Flowers zygomorphic and in some unisexual (Iboza).

5. Calyx gamosepalous and bilabiate.

6. Corolla gamopetalous and bilabiate.

7. Stamens epipetalous and reduced to 2.

8. Gynoecium bicarpellary, syncarpous, axile placentation.

9. One ovule per loculus.

10. Fruit simple.

11. Seeds non-endospermic.

Affinities of Lamiaceae:

Engler, Hallier, Wettestein and Rendle placed the family in Tubiflorae.

The family is closely allied to Acanthaceae from which it can be distinguished by the following features:

1. Quadrangular stem and aromatic smell.

2. Verticellaster inflorescence.

3. Didynamous stamens.

4. Gynobasic style, tetralocular ovary and carcerulus fruit.

The construction of the flower shows that the family is an advanced one among the gamopetalae. Hutchinson therefore placed it at the end of the gamopetalae.

Common plants of the family:

1. Coleus aromaticus (H. Ajwain):

An aromatic herb with beautiful variegated leaves.

2. Leucas lantana:

Herb clothed with white tomentose hairs.

3. Lavandula vera:

Aromatic smell; flowering shoots yield volatile oil.

4. Mentha piperata (H. Podina):

Cultivated, branching herb, perennate by means of suckers.

5. Roylea:

Woody undershrub with white pinkish flowers.

6. Ocimum santcum (H. Tulsi):

Sacred plant for Hindus; also used medicinally.

7. Salvia:

Cultivated ornamental herb.

8. Thymus vulgaris:

Aromatic procumbent shrub; yields oil of much medicinal importance.

Division of the family and chief genera:

Group I: Style gynobasic.

Subfamily 1. Ajugoideae, Seed non-endosporic, e.g., Ajuga.

Subfamily 2. Prostentheroideae. seed endospermic e.g. Prostantherea, Wixonia, etc.

Group II: Style gynobasic.

Subfamily 3. Prasiodideae. Nutlets drupaceous, e.g., Prassium, Stenogyne etc.

Sub-family 4. Scutellarioideae. Nutlets dry with their pericarp, seed transverse, e.g., Scutellaria etc.

Sub-family 5. Lavenduloideae. Nutlets dry, mature anther 1-called seed erect, e.g., Lavendula.

Sub-family 6. Stachydoideae. Same as above but stamens attached on the upper lip. e.g., Solvia etc.

Sub-family 7. Ocimoideae. Like 6 except that the stamens attached on the lower lip. e.g. Ocimum, Hiptis etc.

Sub-family 8. Catopheriodideae. Radicle curved lying against the cotyledons, e.g., Catophoria.

Important Types of Lamiaceae:

1. Ocimum santcum (Fig. 85.1):

Habit:

A perennial herb with strong aromatic smell.

Root:

Tap, branched.

Stem:

Herbaceous above and woody below, aerial, erect, solid, quadrangular, branched, hairy with aromatic smell.

Leaves:

Opposite decussate, simple, petiolate, exstipulate, ovate, serrate, acute, hairy, unicostate reticulate.

Inflorescence:

A verticillaster.

Flower:

Bracteate and bracteolate, pedicellate, complete, hermaphrodite, zygomorphic, pentamerous, hypogynous bilabiate, small and pink.

Calyx:

Sepals 5, gamosepalous, bilabiate (1/4), posterior or upper lip broad and lower or anterior lip with small sepals; gland dotted, violet green, imbricate aestivation.

Corolla:

Petals 5, gamopetalous, bilabiate (4/1), corolla tube short, upper lip of 4 petals and lower of 1 petal; pink, imbricate aestivation.

Androecium:

Stamens 4, polyandrous, epipetalous, didynamous 2+2, anthers versatile; anterolaterals are longer and two postero-lateral are smaller, each postero-lateral has elongated connective bearing fertile anther lobe at the posterior side and sterile lobe at the anterior side; dithecous, introrse.

Gynoecium:

Bicarpellary, syncarpous, superior, bilocular but becoming tetralocular, axile placentation, one ovule in each loculus; style gynobasic; stigma bifid.

Fruit:

Carcerulus.

Seed:

Non-endospermic.

Floral formula:

2. Salvia officinalis:

Habit:

An annual, cultivated herb.

Root:

Tap, branched.

Stem:

Herbaceous, aerial, erect, solid, grooved, quadrangular, hairy, branched.

Leaves:

Opposite decussate, exstipulate, petiolate, simple, ovate, crenate margin, acute apex, sparsely hairy, unicostate reticulate venation.

Inflorescence:

Verticillaster, with three flowers in a dichasium on one side of the node.

Flower:

Bracteate, pedicellate, complete, hermaphrodite, zygomorphic, pentamerous and hypogynous.

Calyx :

Sepals 5, gamosepalous, petaloid, bilabiate, (3/2) i.e. upper lip of 3 lobes and lower of 2 lobes, persistent, hairy, and imbricate.

Corolla:

Petals 5, gamopetalous, bilabiate, (2/3) upper lip of 2 lobes and lower of 3 lobes, imbricate, purple and showy.

Androecium:

Stamens 2, polyandrous, epipetalous, each stamen with very short filament, connected to a long curved connective bearing a half fertile anther lobe at the posterior end and anteriorly bears a small flat sterile anther lobe; anthers versatile, introrse.

Gynoecium:

Bicarpellary, syncarpous, superior, quadrilocular, one ovule in each loculus, axile placentation; style gynobasic; stigma bifid, honey disc is present below the ovary.

Floral formula: