In this article we will discuss about:- 1. Characters of Arecaceae 2. Distribution of Arecaceae 3. Economic Importance 4. Affinities 5. Important Type.
Characters of Arecaceae:
Mainly trees with stout unbranched stem ending in crown of leaves; leaves large, compound, alternate, young leaves are plicate, exstipulate with long petioles; inflorescence enclosed in a persistent spathe; flowers unisexual; perianth 6 in two whorls of 3 each; in male flower 6 stamens in two whorls, anthers versatile; in female flowers carpels three; apocarpous or syncarpous, superior, trilocular or rarely unilocular; fruit berry or drupe; seed endospermic.
A. Vegetative characters:
Habit:
Large unbranched trees (Phoenix, Areca catechu), shrubs or garden palms, trailing (Calamus), herbs (Reinhardtia).
Root:
Adventitious roots arising from the base of bulbous stem. Thick aerial roots are also found in some species of Manicaria.
Stem:
Aerial, woody, erect, unbranched, very rarely branched, (Hyphaene), in some short rhizome (Nipa), cylindrical, hairy, old stem protected by woody leaf bases, climbing (Calamus).
Leaves:
Alternate crowded at the apex of stem giving palmlike appearance to the plant; petiolate, leaf-base sheathing, broad and persistent; exstipulate, compound pinnately (Phoenix, Areca), palmately (Borassus), acute, thick, leathery, parallel venation. In some palms (Copernica) the petiole is prolonged into a ligule like structure called histula.
B. Floral characters:
Inflorescence:
It is simple or compound, spike or branched panicle, usually a spadix with a woody spathe which opens by two valves; spadix may have sessile or pedicellate flowers, simple racemose (Borassus), or compound racemose (Cocos) or even profusely branched panicle (Daemonorops).
Flower:
Sessile or shortly pedicellate, bracteate, mostly unisexual (Phoenix) or hermaphrodite (Livingstonia), actinomorphic, incomplete or complete, hypogynous trimerous, flowers are of small size and produced in large numbers. Plant may be monoecious or dioecious.
In monoecious flower the position of male and female flowers is variable i.e. male flowers at the base or at the apex and the female flowers at the upper part (Ruffia, Rap his) or male and female flowers are inter-mingled or female flowers in the centre, made on the either side as the Cocos, Caryota.
Perianth:
Tepals 6, in two whorls of 3 each, polyphyllous or slightly connate at the base; perianth lobes tough, persistent, coriaceous, leathery or fleshy, valvate or imbricate aestivation, white or petaloid.
Androecium:
In male or hermaphrodite flowers, stamens are 6 in number, two whorls of 3 each, polyandrous, staminodes may be present in the female flowers; anthers versatile, dithecous, basifixed or dorsifixed, introrse, filament short and distinct.
Gynoecium:
In female or hermaphrodite flower-carpels 3 in number, apocarpous or syncarpous, ovary superior, trilocular, axile placentation, single ovule in each loculus; style short, stigma small or broad or 3 lobed.
Fruit:
Usually a berry, fleshy or fibrous waxy coating on the fruit; the mature fruit contains a single seed (Phoenix); drupe (Cocos nucifera).
Seed:
Endospermic.
Pollination:
Anemophilous or entomophilous.
Distribution of Arecaceae:
The family is commonly known as “Palm family”. It includes 217 genera and 2500 species. The members are confined to tropics in both the hemispheres and extending in the warmer regions of the world. In India it is represented by 225 species belonging to 25 genera.
Economic Importance of Arecaceae:
1. Food:
Pith of Metroxylon rumphii and M. leave (Sago palm) yield sago of commerce. The sap of Borassus yields a sugar, which on fermentation gives alcoholic drink “Toddy”. Fruits of Phoenix dactylifera are very delicious and eaten throughout the Arab world. The nuts of Areca catechu serve as a asteringent and used with betel leaves. The milk of Cocos nucifera makes a refreshing drink, endosperm is eaten raw and stored when dry.
2. Medicinal:
Tender leaves of Calamus travancoricus are given in bilousness, worms and dyspepsia.
3. Fibres:
Mesocarps of the drupes of Coconut are extensively used for stuffing pillows and sofa sets. The cane of commerce is obtained from Calamus tenuis and C. rotang and are used for making mats, baskets and other furniture.
Borassus flabellifer – yields palmyra fibres which are used to prepare brushes and brooms. The leaves are used in the manufacture of hand fans, umbrellas, baskets and mats.
4. Wax and oil:
Wax is obtained from the leaves of Copernicia cerifera and Ceroxylon andicola. The wax is used in making gramophone records, candles and models.
Coconut oil is obtained from the Cocos nucifera and is used as hair oil, in soap industry and also for cooking.
5. Ornamentals:
Roystonea regia (Royal palm), Corypha elata (Talipot palm).
Primitive characters:
1. Mostly plants are trees.
2. Leaves are spirally arranged.
3. Flowers are actinomorphic, hypogynous and hermaphrodite.
4. Gynoecium is apocarpous (Phoenix, Rhapis).
5. Ovary superior.
Advanced characters:
1. Small herbaceous forms are also present.
2. Leaves are compound and exstipulate.
3. Inflorescence is a spadix.
4. Perianth is present.
5. Flowers are usually unisexual (Phoenix, Cocos).
6. Flowers trimerous.
7. Stamens epiphyllous.
8. Gynoecium tricarpellary, syncarpous rarely unilocular.
9. Style very short or absent.
10. Axile placentation.
According to Eames (1961) “The palms give evidence of great age; they are primitive taxon that has become greatly diversified and advanced in many characters, each character giving evidence of long specialization.”
Affinities of Arecaceae:
Rendle placed the family together with the Araceae under Spadiciflorae due to unisexual flowers and occurrence of spadix.
Hutchinson (1959) traces the origin of Palms from Liliflorean stock directly from Liliaceae through Dracaena-Cordyline. Erdtman also reports similar pollen structure of Palms and Dracaena.
Palmaceae is closely related to Liliaceae in palm-like habit of Yucca, Dracaena of Liliaceae, perianth segments, stamens in two whorls, tricarpellary, syncarpous ovary, and structure of pollen grains (Dracaena).
Common plants of the family:
1. Areca catechu (H. Supari; Betelnut palm): Graceful single stemmed palm.
2. Caryota urens (Fish-tail palm): Toddy is tapped from its stem.
3. Corypha umbraculifera (Talipot palm): Planted in gardens.
4. Cocos nucifera (H. Nariyal): a tall palm, widespread along sea shore in tropics and sub-tropics.
5. Calamus tenuis and C. rotang (H. Bent): climbing palm.
6. Metroxylon: Fruits take 3 years to mature and pith yields ‘sago’.
7. Nipa fruitcans (Water coconut): palm with delicate round leaves used as cigarette paper; stemless palm of Sunderbans.
8. Phoenix dactylifera (Date palm): tall palm with rough trunk due to persistent leaf bases; fruits are delicious.
Division of the family and chief genera:
The family Arecaceae is divided into seven tribes as follows:
Tribe 1. Areceae:
Leaves pinnatisect; flowers hermaphrodite; fruit a berry or fibrous drupe e.g. Areca.
Tribe 2. Borassieae:
Leaves pinnatisect; flowers unisexual, e.g. Borassus.
Tribe 3. Cococeae:
Leaves pinnatisect; flowers hermaphrodite, fruit fibrous drupe not covered with scales e.g. Cocos.
Tribe 4. Phoeniceae:
Leaves pinnatisect; flowers unisexual; fruit one seeded berry e.g. Phoenix.
Tribe 5. Phytelephanteae:
Leaves pinnatisect; male and female inflorescences separate e.g. Nipa.
Tribe 6. Lepidocaryeae:
Leaves palmatisect or pinnatisect; spadices terminal or interfoliar e.g. Calamus.
Tribe 7. Sabaleae:
Leaves palmatisect; flowers unisexual or bisexual, e.g. Corypha.
Important Type of Arecaceae:
Phoenix sylvestris (Date palm) (Fig. 111.2):
Habit:
A tree.
Root:
Adventitious.
Stem:
Aerial, woody, erect, cylindrical, rough, covered with persistent leaf bases, unbranched, solid, brown.
Leaves:
Forming a dense terminal crown, exstipulate, compound, unipinnate, petiolate, glabrous.
Leaflets:
Sub-sessile, lanceolate, entire, acute, unicostate parallel venation.
Inflorescence:
Spadix-branched, erect, long, enclosed by spathe.
Flower:
Small, actinomorphic, hypogynous, unisexual, bracteate, incomplete.
Male Flower:
Bracteate, sessile, incomplete, numerous, angular, actinomorphic, hypogynous, trimerous.
Perianth:
Tepals 6, in two whorls of 3 each, white, angular, free and inferior.
Androecium:
Stamens 6, in two whorls of 3 each, polyandrous, filament short; anthers dithecous, dorsifixed, introrse.
Gynoecium:
Absent.
Female flower:
Bracteate, sessile, incomplete, actinomorphic, hypogynous, trimerous.
Perianth:
As in male flower.
Androecium:
Absent.
Gynoecium:
Tricarpellary, syncarpous, ovary superior, one ovule in each carpel; style absent; stigma hooked.
Fruit:
One seeded berry, orange yellow.
Seed:
Hard and endospermic.
Floral formulae:
