ADVERTISEMENTS:
In this article we will discuss about:- 1. Characters of Orchidaceae 2. Distribution of Orchidaceae 3. Economic Importance 4. Affinities 5. Important Type.
Characters of Orchidaceae:
Perennial herbs, epiphytes or saprophytes may be terrestrial; flowers zygomorphic, hermaphrodite, epigynous, resupinated; perianth 6 in two whorls, the posterior segment of the inner whorl developed as lip or labellum; presence of peculiar structures – Labium, column and Rostellum; Stamens 1-2, one or two staminode pollengrains united into pollinia; gynoecium tricarpellary, inferior unilocular with parietal placentation; the fertile stamen is adherent to the style and forms with it the column or gynostemium, which projects more or less in the centre of flower; Stigma 2 or 3 lobed, in some two fertile and one sterile and modified into rostellum.
A. Vegetative characters:
ADVERTISEMENTS:
Habit:
Perennial terrestrial, succulent, scapose herbs; many are epiphytic or saprophytic, sometimes climbers Vanilla.
Root:
Adventitious, tuberous, (Orchis), fleshy, climbing or aerial. Main roots always absent.
ADVERTISEMENTS:
Stem:
Erect, sometimes climbing or trailing, annual in terrestrial forms, perennial in epiphytic forms; generally thickened into rhizome or pseudobulbs (Phajus, Bulbophyllum), bearing aerial assimilatory roots. (Taeniophyllum).
Leaf:
Simple, alternate, sometimes opposite or whorled, usually fleshy, linear to ovate, sheathing base, sometimes reduced to achlorophyllous scales.
B. Floral characters:
Inflorescence:
Solitary or spike, racemes or panicle (Oncidium).
Flower:
Flowers are of variable and peculiar, shape, size and colour, often showy, bracteate, zygororphic, bisexual or rarely unisexual, eipgynous, trimerous, mostly resupinate i.e. twisted to 180° or upside down.
ADVERTISEMENTS:
Perianth:
Tepals 6, in two whorls of each, outer 3 tapals (representing calyx) green; inner 3 tepals coloured (representing corolla), dissimilar-the 2 lateral or wings like, the third posterior tepals is lightly modified often projected basally the labellum or lip; broad, shoe-like spursed, tubular, strap-shaped or butterfly shaped or variously branched and contributing most to the oddity and beauty of the flower.
The labellum is actually posterior it comes to lie on the anterior side of the flower due to twisting (or resupinationl) of the inferior ovary through 180° or by the bending back of pedicel over the apex of the stem.
Androecium:
ADVERTISEMENTS:
Stamens 3, which unite with the pistil to form a column, the gynandrium or gynostemium opposite to the labellum; functional stamen (Orchis) or 2 (Cypripedium), bithecous, introrse; pollen granular or coherent in each cell into one, 2 or 4 stalked pollen masses or pollinia.
A connection between ovary and stamen is made by the beak-like sterile stigma; occupying almost the centre of the column. Sometimes staminodes are also present.
Gynoecium:
Tricarpellary, syncarpous, ovary inferior, unilocular, parietal placentation, rarely trilocular and axile placentation (Apostasia); stigmas 3, of which 2 lateral are often fertile, the third stigma is sterile forming a small beaked outgrowth – the rostellum lying in the centre of column between the anther and fertile stigma. In Cypripedium and Paphiopedium, all the 3 stigmas are functional.
ADVERTISEMENTS:
Fruit:
A capsule.
Seed:
Small, light (0.004 gm. each), non-endospermic.
ADVERTISEMENTS:
Pollination:
Entomophilous.
Floral formula:
Distribution of Orchidaceae:
It is second longest family of angiosperms. It is represented by about 900 genera and 20,000 species, which are cosmopolitan in distribution. In India it is represented by about 130 genera and over 800 species. The family 13 having great variety of flowers in shape, longevity and beauty.
Economic Importance of Orchidaceae:
1. Food:
ADVERTISEMENTS:
During scarcity the tuberous roots of Habenaria susannae and Orchis latifolia are used as food.
2. Flavour:
The capsules of Vanilla planifolia V. fragrans yield commercial ‘Vanilla’ a flavouring agent for chocolate and confectionary.
3. Medicine:
The root-stocks of Eulophia epidendraeas are used as vermifage.
4. Dye:
ADVERTISEMENTS:
The leaves of Calanthe veratrifolia contain a glycoside ‘indican’, which on hydrolysis yields ‘indigo blue’.
5. Ornamentals:
Many orchids are cultivated in the green houses for their beautiful sweet-scented flowers of various forms, shapes with highly attractive labellum of various hues and bright clours. The orchid flowers are in great demand and are much more sought after than any other flowers.
Hence extensively grown from a commercial point of view. Some commonly grown orchids are – Cypripedium (lady’s slipper), Epidendrum (Green-fly orchid) Habenaria (fringe- orchid), Oncidium (butterfly orchid), Vanda, Vanilla, Odontoglossum (lady orchid).
Primitive characters:
1. Plants are perennial by means of pseudobulbs or root-tubers.
2. Leaves simple.
3. Presence of large, coloured and scented flowers.
4. Flowers solitary, terminal and bisexual.
5. Parietal placentation.
6. Entomophilous pollination.
7. Ovules numerous.
Advance characters:
The Orchidaceae is agreed upon by almost all botanists to be the most advanced family in the monocots for the following reasons:
1. It is an immense family of 20000 species.
2. Plants only herbs that are widely distributed and successfully invaded in various situations. Cosmopolitan all over the globe.
3. Leaves exstipulate.
4. Adventitious roots-variously modified.
5. Flowers of diverse shape, size and colour, small and incospicuous.
6. Flowers zygomorphic due to labellum, which is variously modified.
7. Epigynous flowers.
8. Reduction in number of stamens to two or one.
9. Adhesion of stamens with style and stigma to form-column.
10. Gynoecium 3, syncarpous and inferior.
11. Reduction in the number of fertile lobes of stigma to 2.
12. Modification of third sterile lobe of stigma into a structure called restellum.
13. Pollen-grains are agglutinate into pollinia.
14. Fruit is a simple capsule.
15. Seeds non-endospermic, minute-and light in weight.
Affinities of Orchidaceae:
Orchidaceae was included by Bentham and Hooker as the third family of Mocrosporae at the beginning of the Monocotyledons. Hutchinson (1959), Takhtajan (1969) and Cronquist (1981) placed the family under the order Orchidales. Thorne (1983), placed Orchidaceae under the suborder Orchidineae of the order Liliales.
The Orchidaceae is related to the epigynous components of the Liliiflorae (Liliales). The Orchidaceae has beerl also believed to arise from the Musaceae or its ancestor.
Several taxonomists consider Orchidaceae to be the most advanced and highest evolved among monocotyledons.
Common plants of the family:
1. Calanthe (Gk. calos-beautiful, anthos-flower)-beautiful flowers, occurs in the hills of S. India.
2. Acampe praemorsa and Vanda roxburghii are epiphytic.
3. Cattleya – Corsage orchid, cultivated for showy flowers.
4. Corallorhiza – Coral-root orchid, a saprophyte with branched and fleshly rhizome.
5. Vanilla planifolia – Vanilla orchid, cultivated in S. India for perfumery & confectionary.
6. Cypripedium calceolus – Lady’s slipper orchid; slipper-like with inturned edges.
Division of the family and chief genera:
The Orchidaceae is divided into two sub-families:
Sub-family I. Diandroideae:
Stamens 2 belonging to the lateral members of the inner whorl, the 3rd of the same is modified to a staminode placed above the anthers; the members of the outer whorl of androecium are either suppressed or represented as staminodes. Stigmas 3, fertile. This subfamily has only one tribe.
Tribe (i) CYPRIPEDEAE. Genera: Paphiopedilum, Cypripedium. etc.
Subfamily II. Monandrae:
Stamen is only 1 belonging to the outer whorl, all others are suppressed, sometimes the lateral members of the outer whorl are represented as staminodes, this has been further divided into groups, tribes and subtribes.
Group A. Basitonae:
Caudicle and viscidium arising from the base of pollinia; anthers erect or turned more or less to the angle 180 (resupinate), very closely attached to the wide based column, never deciduous after flowering. Pollinia not waxy.
Tribe (i) Ophrydeae. Genera: Habenaria, Orchis, etc.
Group B. Acrotonae:
Caudicle and viscidium arising from the tip of the pollinia; anthers erect or incumbent, filament sort, slender, usually narrowly attached to the column, deciduous, if persistent then very early drying. The Acrotonae is further subdivided into many tribes and subtribes.
Important Type of Orchidaceae:
Zeuxine strateumetia (Fig. 100.1):
Habit:
A small 5.25 cm. high, glabrous, terrestrial herb.
Root:
Short tuberous.
Stem:
Herbaceous, arise from underground rhizome, erect, unbranched, cylindrical, glabrous and green.
Leaf:
Simple, exstipulate, sessile, alternate, sheathing leaf-base, membranous, linear, entire, acuminate, parallel veination.
Flower:
Bracteate, zygomorphic, hermaphrodite, epigynous, small, resupinate at maturity.
Perianth:
Tepals 6, in two whorls of 3 each, subequal, polyphyllous, superior, anterior tepal of outer whorl large and concave; posterior tepal of inner whorl quite distinct, saccate, forming labellum, adnate to the base of column, inner whorl imbricate and outer valvate.
Androecium:
Stamen one, united to the style to form gynostegium, opposite the labellum, column short with a pair of wings covering the anther, anther modified into one pair of pollinia, which are attached by a stalk (caudicle) the corpusculum; two staminodes attached to the base of anther, one on either side; stamen connected to the ovary by rostellum.
Gynoecium:
Tricarpellary, syncarpous, inferior, unlocular, parietal placentation, two fertile stigma on the top of the column, carpel twisted.
Fruit:
A capsule.
Floral formula:
