In this article we will discuss about:- 1. General Features of the Araceae 2. Floral Range in the Araceae 3. Divisions 4. Position and Affinity 5. Number and Distribution 6. Commonly Occurring Plants 7. Economic Aspects.
General Features of the Araceae:
Habit – Herbs with an acrid watery latex, sometimes epiphytic with aerial roots or shrubby with corms, rhizomes and tubers.
Leaves – Radical or cauline, simple or compound, often broad, long-petioled, net-veined.
Inflorescence – Spadix, subtended by a spathe.
Flowers – Bisexual or unisexual, small, often with a foetid smell.
Perianth – Absent or present.
Androecium – Stamens 2, 4 or 8, opposite to perianth segment, free or united; anthers mostly 2-celled.
Gynoecium – Carpels 1-3; ovary sunk on peduncle of spadix, ovary superior, 1- to 3-locular; ovules few to many in each loculus; placentation parietal.
Fruit – Berry.
Seeds – Albuminous, embedded in a mucilaginous pulp or exalbuminous; embryo minute, straight.
Floral Range in the Araceae:
The flowers are bisexual and naked in Calla. They may be unisexual and naked with female flowers on the lower and male on the upper parts of the spadix, as in Arum, Alocasia, Colocasia, etc. In Acorus. the flowers are bisexual and characterised by a trimerous arrangement. On the contrary, the flowers may have dimerous whorls, e.g., Anthurium or have dimerous whorls with a solitary carpel, e.g., Gymnostachys.
The spathe is of various colour. It is petaloid in Richardia. It is green in Alocasia, Colocasia and related genera. It is scarlet in Anthurium.
The perianth may be present or absent; the former case is found usually in bisexual flowers and the latter in unisexual flowers. The perianth segments are free in Acorus and united in Spathiphyllum.
The androecium may form a single whorl or double whorl of stamens. When there is a single whorl, the filaments are somewhat united at the base as in Arisaema, Dracunculus, etc.
In Alocasia, Colocasia and other genera, the filaments are united throughout their length to form a synandrium. In Pistia, the male flower is reduced to 2 anthers which are connate. Sometimes, there are staminodes in the female flowers. Arisarum and Biarum are in possession of a solitary stamen.
The gynoecium consists of 3 carpels. A single carpel is seen in Arum, Pistia, etc. The ovary may be unilocular or multilocular. The number of ovules may be few to many in each loculus. The placentation is also diverse, such as axile, marginal or parietal.
Divisions of the Araceae:
The Araceae is divided into eight subfamilies:
Subfamily I Aroideae:
Land or marsh plants. Leaves various, net-veined. Latex-sacs straight. Flowers with or without perianth. Stamens free or in synandria. Examples- Arum, Typhonium, etc.
Subfamily II Colloideae:
Land or marsh plants. Leaves never sagittate. Latex-sacs present. Flowers bisexual, naked. Example- Calla.
Subfamily III Colocasioideae:
Land or marsh plants. Leaves always net-veined, never sagittate. Latex-sacs branched. Flowers unisexual, naked. Stamens in synandria. Examples- Alocasia, Colocasia, etc.
Subfamily IV Lasioideae:
Land or marsh plants. Leaves sagittate, often much-lobed, net- veined. Latex-sacs present. Flowers bisexual or unisexual. Examples- Amorphophallus, Lasia, etc.
Subfamily V Monsteroideae:
Land plants. Latex-sacs absent, but spicular cells present. Flowers bisexual, naked. Examples- Monstera, Scindapsus, etc.
Subfamily VI Philodendroideae:
Land or marsh plants. Leaves always parallel-veined. Flowers bisexual or unisexual. Examples- Philodendron, Richardia, etc.
Subfamully VII Pistioideae:
Swimming plants. Leaves parallel-veined. Flowers extremely reduced. Example- Pistia.
Subfamully VIII Pothoicieae:
Land plants. Latex-sacs and spicular cells absent. Flowers bisexual. Examples- Acorus, Pothos, etc.
Position and Affinity of the Araceae:
Bentham-Hookcr 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, as comprising his seventh order Spathiflorae on account of the universal presence of a spathe.
Rendle included the family in his fifth order Spadiciflorae on the basis of the spadix inflorescence and unisexual flowers. In Hutchinson’s arrangement, the family appeared under his 97th order Arales; the criteria for assigning such a position were the same as those used by Rendle. Both the Araceae and Lemnaceae have been considered under the superorder Arecanae and the order Arales by Takhtajan and Dahlgren.
The Araceae is closely related to the Palmae 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 subject of much dispute. Lotsy suggested that the family, together with the Palmae and Pandanaceae, arose from the Piperales. Engler felt that the family was a derivative of the Palmae via the Cyclanthaceae. Wettstein regarded the family to be more advanced than the Orchidaceae and to be originating from the Helobiae-Liliiflorae stocks.
Bessey opined that the Palmae and Araceae represented parallel or diverge development from liliaceous ancestors. Hutchinson expressed the idea that the family developed directly from the Liliaceae through the tribe Aspidistreae and parallel with the Palmae but along different lines.
Number and Distribution of the Araceae:
The Araceae is composed of about 110 genera and 2,000 species. The members of this family are mostly abundant in tropical regions, but also found in temperate zones.
Commonly Occurring Plants of the Araceae:
Sweet Flag (Acorus calamus L.) is an erect aromatic marshy herb, having a thick creeping rootstock.
Alocasia indica (Roxb.) Schott. is a terrestrial herb with a suberect thick rhizome.
Teliga Potato [Amorphophallus campanulatus (Roxb.) Bl. ex Decne] is a terrestrial herb with a roundish warty thick corm.
Snake Plant [Arisaema tortuosum (Wall.) Schott.], seen in Darjeeling, is characterised by a greenish purple spathe which expands over the spadix like the hood of a snake; it is an instance of mimicry.
Caladium bicolor (Ait.) Vent is often planted in gardens.
Common Arum or Taro [Colocasia esculentum (L.) Schott.] is a terrestrial herb with a tuberous rhizome.
Cryptocoryne spiralis (Retz.) Fisch. ex Wyndler, an aquatic herb on the muddy banks of the Ganges, exhibits vivipary.
Gonatanthus pumilus (D. Don) Engl. & Krause is found in eastern Himalaya.
Lasia spinosa (L.) Thw. is a stout spinous herb in swampy areas.
Water-cabbage or Water-soldier (Pistia stratiotes L. var. cuneata Engl.) is a floating stoloniferous herb, bearing a rosette of sessile obcordate cuneate leaves and emitting a muriatic odour.
Pothos scandens L. is a gigantic root-climber.
Scindapsus officinalis Schott. is a garden climber.
Typhonium trilobatum (L.) Schott. is a tuberous herb of waste places, having a bright red appendage.
Economic Aspects of the Araceae:
The Araceae is of some importance in the economic sense. The leaves and rootstocks of Acorus calamus are utilised for making perfume and hair powder as well as for giving flavour to beer, gin, vinegar, snuff and other preparations; the rhizomes yield a drug.
The underground stems of Alocasia indica, A. macrorrhiza, Amorphophallus campanulatus, Colocasia esculentum, C. nymphaeifolia, Cyrtosperma chamissonis, Xanthosoma atrovirens, X. sagittifolium and X. violaceum are edible.
The tender leaves of Lasia spinosa are consumed as a food. Monstera deliciosa yields edible fruits. Some plants are cultivated as ornamentals, e.g., Aglaonema, Anthurium, Caladium, Dracunculus, Philodendron, Pothos, Zantedeschia, etc.
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