In this article we will discuss about:- 1. Characters of Araceae 2. Distribution of Araceae 3. Economic Importance 4. Affinities 5. Important Type.
Characters of Araceae:
Plants rhizomatous or tuberous large herb; root-climbers in damp forests; leaves large, lamina incised or perforated, leaf-base sheathing; spadix subtented by spathe; spathe of bright colour; flowers di- or trimerous, unisexual (rarely bisexual), perianth absent or 6 tepals, stamens generally forming synandrium, fruit berry.
A. Vegetative characters:
Usually perennial herb, highly variable as rhizomatous or tuberous herbs Arum climber (Pothos) or tree-like (Philodendron), aquatic (Pistia), epiphytic (Anthurium), marshy (Acorus).
Adventitious, fibrous, usually of two-aerial or epiphytic in climbing plants, (Pothos, Monstera), absorbing and clasping. In the aerial roots, the velamen are also present.
Underground or subterranean, in the form of tubers (Arum), corms (Colocasia) rhizome (Acorus), aerial (Pothos) with often have a pungent taste, aerial showing monopodial or sympodial branching, accessory buds often develop in leaf-axil.
Generally large, measuring 3 metre (Amorphophallus companulatus) radical or cauline, shape and size variable, alternate, simple or compound, petiolate or sessile (Pistia), usually parallel-veined (Acorus) but rarely reticulate (Arisaema), cordate, sagittute or hastate, entire or lobed.
B. Floral characters:
Spadix, subtended by a bract or spathe, it may be more than 1 m long Amorphophallus rivieria, coloured, the upper portion of spadix is usually naked and lower portion bears flower, usually some sterile flowers are present close to male and female flowers i.e. the flowers of both sexes are in distinct zones separated by zone of sterile hair.
Small, sessile, actinomorphic, di- or trimerous, unisexual rarely bisexual (Acorus, Pothos, Mostera), hypogynous or epigynous, often bad-smelling.
Absent (Calla, Colocasia) in unisexual flowers and present in bisexual flowers, 1 (Acorus) or 4 (Anthurium) to 6 (Acorus), perianth lobes small, scale-like, free or rarely connate.
Stamens many or reduced to 4-10, even 1 (Arisaema) in two or one whorl; situated opposite to perianth lobes; free or united into a synandrium (Colocasia, Alocasia) dithecous, introrse, female flowers bear staminodes.
Carpels varied in number, but often reduced to single carpel, ovary superior, 1 to 3-celled, ovules one or more in each cell; placentation may be axile (Pothos) or parietal (Arum) or basal (Typhonium); style short, stigma one or more.
A berry, the cluster densely grouped on the fruiting spadix, looking as a multiple-fruit.
Albuminous, embedded in mucilaginous pulp or exalbuminous.
Entomophillous due to coloured – spathe, rarely self-pollinated (species of Arisaema).
Distribution of Araceae:
It is commonly called Arum family, contain 115 genera and 2000 species. About 25 genera and over 140 species have been reported from India. The members tend to be aquatic but some are epiphytic.
Economic Importance of Araceae:
The plants cultivated for vegetables are Colocasia esculenta (Arvi, Kachalu or Colocasia); Alocasia indica (Mankand), Amorphophallus campanulatus (Zimikand or elephant foot).
Leaves of Lasia spinosa are eaten as food.
The large fruits of Mostera are eaten in many tropical regions. From the tubers of Colocasia esculenta, the starchy baby foods and alcohol are also prepared.
The rhizomes of Acorus calamus are used in diarrhoea and dyspepsia. The stem juice of Alocasia macrorrhiza is used to relieve pain in scorpion bite. The corns of Amorphophallus campanulatus are used in treating piles and dysentry.
Arisaema spp. are poisonous.
The plants of this family are commonly grown in gardens and green houses for their variegated and handsome leaves. The plants are Pothos aureus (Money plant), Monstera deliciosa, Alocasia indica var. metallica, Caladium picturatum, C. bicolor, Colocasia esculenta, Scindapsus officinalis, Anthurium and Pistia spp. in aquaria.
Affinities of Araceae:
Bentham and Hooker placed the Araceae in their fifth series Nudiflorae for the perianth being absent in many genera of the family. Engler treated the family along with the Lemnaceae, on account of the universal presence of spathe. Rendle included the family in order spadiciflorae on the basis of spadix inflorescence and unisexual flowers. In Hutchinson’s arrangement, the family appeared under order Arales.
The Araceae is closely related to the Palmaceae on such grounds as small flowers arranged in a spadix and subtended by a spathe as well as the relative size of the embryo and endosperm. It is also akin to the Lemnaceae which is a replica of the aroids, though an extremely reduced one.
The origin of the Araceae has been a subject of much dispute. Lotsy suggested that the family, together with the Arecaceae (Palmae) and Pandonaceae, arose from the Piperales. Engler felt that the family was a derivative of the Palmaceae via the Cyclanthaceae.
Wettstein regarded the family to the more advanced than the Orchidaceae and to be originating from the Helobiae-Liliiflorae stocks. Hutchinson expressed the idea that the family developed directly from the Liliaceae through the tribe Aspidistreae.
Common plants of the family:
1. Amorphophallus campanulatus (Teligo patato) is a terrestrial herb with roundish, watery thick corms.
2. Arisaema tortuosum (Snake plant) seen in Darjeeling and Shillong, is characterised by a greenish-purple spathe which expands over the spadix like the hood of a snake.
3. Caladium bicolor – Leaves variegated, multicoloured, ornamental garden plant.
4. Pistia stratiotes L. (Water Cabbage) is a floating stoloniferous herb bearing rosettes of sessile obcordate cuneate leaves.
5. Pothos aureus L, (Money plant), a climbing herb without latex. The leaves may be variegated, cultivated.
6. Acorus calamus L. (Sweet flag) is an erect aromatic marshy herb.
7. Monstera deliciosa (“Amarphal”) an ornamental herb or shrub with leaves perforated.
Division of the family and chief genera:
The Araceae is divided into eight sub-families:
Sub-family I. Arodeae:
Latex sacs straight, flowers with or without perianth. Stamens free or in synandria.
Arum, Typhonium, etc.
Sub-family II. Calloideae:
Leaves fever sagittate, Latex sacs present, Flowers bisexual, naked.
Sub-family III. Colocasioideae:
Leaves always net-veinned. Latex sacs branched, Flowers unisexual, naked, Stamens in synandria.
Alocasia, Colocasia etc.
Sub-family IV. Lasioideae:
Leaves sagittate, Latex sacs present. Flowers bisexual or unisexual.
Amorphophallus, Lasia, etc.
Sub-family V. Monsteroideae:
Latex sacs absent, but spicular cells present. Flowers bisexual, naked.
Monestera, Scindapsus etc.
Sub-family VI. Philodendroideae:
Leaves always parallel-veined. Flowers bisexual or unisexual.
Philodendron, Richardia etc.
Sub-family VII. Pistioideae:
Aquatic herbs. Leaves parallel-veined. Flowers extremely reduced.
Sub-family VIII. Pothoideae:
Latex sacs and spicular cells absent, flowers bisexual.
Acorus, Pothos etc.
Important Type of Araceae:
Colocasia esculenta (Fig. 114.1):
Herb, large, coarse and cultivated.
Corms, from main corm arise lateral branches.
Large, ovate-sagittate, spathe, yellow with green base, thick in texture.
Spadix – enveloped in white and yellow spathe.
Unisexual and naked actinomorphic.
Androecium of 6 stamens united into a six-angled synandrium.
Gynoecium of tricarpellary, syncarpous, superior, unilocular, parietal placentation.