In this article we will discuss about:- 1. Characters of Alismaceae 2. Distribution of Alismaceae 3. Economic Importance 4. Affinities 5. Important Type.
Characters of Alismaceae:
Plants aquatic; stem rhizome or runner; leaves radical or whorled, flower hermaphrodite, or unisexual, trimerous, hypogynous; perianth biseriate, the outer whorl (series) clearly sepal-like; stamens 6 to indefinite; carpels free, 3 to indefinite, apocarpous, superficial placentation; fruit etario of-achenes or follicles.
A. Vegetative characters:
Habit:
Annual or perennial herbs of marshy places or floating or submerged aquatic herbs.
Root:
Adventitious, fibrous.
Stem:
A stout underground rhizome or runner.
Leaf:
Radical, long-petioled or stalked, with sheathing leaf-base, simple, lamina linear to ovate or the bases sagittate, reticulate with few to many primary parallel veins, converging apically; sometimes leaves are heterophyllous.
B. Floral characters:
Inflorescence:
A raceme or panicle or corymbose umbel on scape which bears whorls of branches and branchlets bearing stalked flowers.
Flower:
Pedicellate, bractcate, hermaphrodite rarely unisxual, hypogynous, trimerous, often in whorls, regular.
Perianth:
Six in two whorls of 3 each ; outer whorl of 3, green and sepal-like (sepaloid) herbaceous and persistent; 3 inner petaloid large, deciduous, free, imbricate.
Androecium:
Stamens 3 (rarely)-6 or indefinite, free, bithecous, extrorse or dehiscing by bateral slits; in Alisma 6 stamens in three alternipetalous pairs.
Gynoecium:
Carpels 3-6 or more, apocarpous, ovary superior, unilocular with 1 to many ovlues, anatropous or campylotropous, placentation marginal or basal; style mostly articular, and persistent; stigma 1.
Fruit:
Etario of achene, rarely follicular.
Pollination:
It is effected by small insects which are attracted by nector secreted by thick ring-like bases of filaments of stamens.
Seed:
Non-endospermic, minute; embryo horse shoe-shaped with a single bent cotyledon.
Floral formula:
Distribution of Alismaceae:
Alismaceae or the sagittaria family having about 17 genera with over 80 species having a very wide range of distribution, the sub-family Butamoideae is distributed in the temperate and tropical regions of the world.
The sub-family Alismioideae extends from Artie to tropical regions of the earth inducing Australia, Indo-Malaya, Africa, Madagascar, and California. The members are mostly distributed in fresh-water swamps and streams.
Economic Importance of Alismaceae:
1. Food:
Most of the genera provide food for wild life. The tubers of Alisma plantago, roots of Sagittaria latifolia (N. America) and corms of Sagittaria sagittifolia (China, Japan) are edible.
2. Ornamental:
Sagittaria latifolia and S. subulata are grown in aquaria. Many species of Alisma, Echinodorus and Sagittaria are cultivated as decorative plants.
Aiffinities of Alismaceae:
The family Alismaceae has been reckoned as one of the most primitive families of Monocotyledons in the scale of evolution and has been consequently placed first. Engler and Rendle placed it after Pandanales in the second series of Helobieae. The primitiveness of the family is marked in free carpels, numerous stamens and hypogynous flowers.
Alismaceae resembles Ranunculaceae (hypogynous flowers, free sepals and petals numerous free stamens and carpels and also fruit-etario of achenes or follicles) and Commelinaceae but can be distinguished from them by its aquatic habit, form of inflorescence and two whorls of perianth. It also resembles Nymphaeaceae in having superficial placentation; but further affinity is difficult to establish.
Alismaceae, though a monocotyledonous family it bears remarkable affinity with Ranunculaceae and Nymphaeaceae in general construction of flower; this has been proved in the genus Ranalisma (an Indo-Malayan Alismaceae) which bears combination of character of Alismaceae and Ranunculaceae. This possibly supports the origin of Alismaceae from Ranunculaceae or Nymphaeaceae.
Cheadle (1942) found that vessels with simple or porous perforation were the rule in Alismaceae, on anatomical condition more advanced than that found in most other families of the order.
Dahlgen (1983) and Thorne (1983) in their classification made a super-order Alismatiflorae and order Alismales in which they included family Alismaceae.
Common plants of the family:
1. Alisma plantago-aquatica – water plantain – an aquatic plant with hermaphrodite flowers.
2. Limnophyton obtusifolium-anquatic plant with white unisexual flowers.
3. Sagittaria sagittifolia – Arrow head-a tank herb with sagittate leaves and unisexual flowers.
Division of the family and chief genera:
Subfamily I:
Alismoideae. ovule solitary in each carpel, rarely 2 or more, marginal placentation. Genera: Alisma, Sagittaria, etc.
Subfamily II:
Butomoideae. ovules many in each carpel, placentation superficial. Genera: Butomopsis, Hydrocleis, etc.
Important Type of Alismaceae:
Sagittaria sagittifolia:
Habit:
Aquatic tank herb.
Root:
Adventitious.
Stem:
A stout rhizome.
Leaves:
Radical sagittate, long petiolate, with sheathing leaf-base, simple, reticulately veined with few to many primary parallel veins converging apically.
Inflorescence:
Panicle on scape which bears whorls of branches and branchlets.
Flower:
Pedicellate, unisexual, hypogynous, trimerous, globose receptacle.
Perianth:
6 in two whorls of 3 each, outer whorl of 3, green, free, sepal-like and 3 inner, petaloid, large, free, imbricate.
Androecium:
In male flower-stamens many, free bithecous, extrorse.
Gynoecium:
In female flower-carpels many, apocarpous, ovary superior, marginal placentation.
Fruit:
Achene.
Floral formulae:
