In this article we will discuss about:- 1. General Characters of Araceae 2. Floral Formula of Araceae 3. Number and Distribution 4. Range of Floral Structures 5. Common Plants 6. Affinity and Economic Importance.
General Characters of Araceae:
Plants—usually terrestrial herbs (but aquatic in Pistia), often large or even tree-like, rarely shrubs, sometimes climbing, generally with acrid watery latex. Stem—rhizomatous, tuberous or corm-like, resin passages and mucilage sacs sometimes occur. Leaves—radical or alternate (in climbing species), generally net-veined, sometimes long and narrow with parallel veins (e.g., Acorus calamus).
Inflorescence—spadix with a spathe which may be green (e.g., Colocasia), petaloid (e.g., Richardia), or brilliant scarlet (e.g., Anthurium). Flowers—small, inconspicuous with dimerous or trimerous whorls, bisexual or unisexual, closely crowded on the spadix without bracteoles, mostly zoophilous.
Perianth—absent (in unisexual flowers) but present in bisexual flowers, of 4-6 scales which may be free or united. Stamens— 2, 4 or 8, with the filaments more or less united at the base (e.g., Arisaema), or throughout their length (e.g., Colocasia, Alocasia), or to a single stamen (e.g., Arisarum); in Pistia the male flower is reduced to two anthers which are united; staminodes sometimes present in the female flowers.
Carpels—(3), usually reduced to one (e.g., Colocasia, Pistia); ovary superior, sometimes inferior, 1-many-celled, ovules few to numerous in each cell on basal, parietal or axile placentae; stigma 1 or more. Fruit—berry. Seed—albuminous, embedded in a mucilaginous pulp, or exalbuminous. Embryo—minute and straight.
Floral Formula of Araceae:
Number and Distribution of Araceae:
This family consists of about 105 genera and about 1,500 species which are generally found in the temperate and tropical regions but especially developed in the warmer regions of the globe.
Range of Floral Structures in Araceae:
This family shows great variations in floral structures. The flowers are bisexual with typical trimerous arrangement P3+3A3+3G(3) (e.g., Acorus), or with dimerous whorls (e.g., Anthurium), or dimerous arrangement with reduction to one in gynoecium (e.g., Gymnostachys). The flowers are bisexual and naked, as in Calla, or unisexual and naked with male flowers on the upper and female on the lower portions of the spadix, as in Colocasia, Alocasia and others.
The spathe is green, as in Colocasia, or petaloid, as in Richardia, or it assumes brilliant scarlet colour, as in Anthurium.
Perianth is either present or absent. The perianth leaves are united (e.g., Spathiphyllum), or free (e.g., Acorus). They are generally absent in unisexual flowers but are present in bisexual flowers.
Androecium forms two whorls or a single whorl and in the latter case, the filaments are connate to some extent at the base (e.g., Dracunculus, Arisaema), or filaments are united throughout their length and form a synandrium, as in Colocasia, Alocasia. The male flowers are found to be reduced to form synandrium by two anthers, (e.g., Pistia). In Arisarum and Biarum, there is a single stamen.
Carpels are generally three, but one carpel is present in Colocasia and Pistia. Ovary is superior or sessile. The ovary becomes 1-many chambered with few to indefinite ovules.
The placentation may be of various types, such as parietal, axile or marginal.
Common Plants of Araceae:
(1) Common Arum or Taro (Colocasia antiquorum Schott. = C. esculenta Schott.), a herb chiefly cultivated for its edible rhizome.
(2) Alocasia indica Schott., also cultivated for its rootstock.
(3) Scindapsus officinalis Schott., a root-climber of gardens.
(4) Typhonium trilobatum Schott., commonly found in waste places.
(5) Teliga potato (Amorphophallus campanulatus Bl.), commonly cultivated for the edible corm, also found wild.
(6) Water lettuce (Pistia stratiotes L.), a common floating herb with rosettes of radical leaves.
(7) Cryptocoryne ciliata Fisch., an aquatic herb on the muddy banks of the Ganges, characterized by the viviparous mode of germination of the seeds.
(8) Pothos scandens L., a gigantic root-climber, common in gardens.
(9) Arum lily (Richardia ethiopica Kunth.), a herb with thick rootstock and large white trumpet-like spathe; very common in Darjeeling.
(10) Arisaema speciosum Mart., grows in Darjeeling and has a long tail and a spotted hood-like spathe which looks like a fearful snake from a distance, an instance of mimicry.
(11) Lasia heterophylla Schott., occurs in swampy places.
Affinity and Economic Importance of Araceae:
Hutchinson is of opinion that Araceae has been developed as a separate phylum from Liliflorae. Lotsy assumes that Palms, Aroids and Pandanales have been derived from the Piperales. Such contrast with Piperaceae is mainly based on the floral structure and inflorescence of the latter which simulate with such trend of Araceae.
The plants of this family, though strikingly different in general habit, are closely allied to Palmae in such important characters, as the relative size of the embryo and endosperm, while in both we notice the large development of the spathe and the association of a large number of small, inconspicuous flowers in often huge, indefinite inflorescences.
Araceae, on the other hand, is closely allied to Lemnaceae which is evidently a much reduced member of Aroid type, the reduction proceeding so far as to affect the vegetative and reproductive organs.
Economic Importance of Araceae:
This family consists of several economic plants. An aromatic essential oil is obtained from Sweet flag (Acorus calamus). The underground stems of Colocasia, Alocasia and Amorphophallus are eaten as vegetables. A kind of fibre is derived from the stem of Scindapsus. The fruits of Monstera are often taken for delicate flavour. Some plants are cultivated as ornamentals, such as Philodendron, Anthurium, Caladium, Pothos, Scindapsus, etc.
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