ADVERTISEMENTS:
In this article we will discuss about the Classification of Spathiflorae. According to Engler and Prantl, Spathiflorae consists of two families:- 1. Araceae 2. Lemnaceae.
Family # 1. Araceae:
Araceaeare are herbs with tuberous rhizome or corm, or stem short and erect, often woody, or climbers, sometimes epiphytic; unarmed or rarely with spines or thorns; laticiferous tissues present, mostly associated with sieve tubes; while those are absent, raphides are present in the intercellular spaces; the latex is watery and acrid, or it is milky.
The stem has a sympodial growth while in Pistia it is monopodial. The roots are adventitious; in climbing species absorbent roots and clasping roots are found.
ADVERTISEMENTS:
Aerial roots with velamen also occur in some species. Leaves crowded at the apex of rhizome or erect stem, or along the stem in the climbers and alternate, dstichous in Pothos; simple or pinnate or digitate; usually petiolate, sheathing at the base, generally net- veined but parallel-veined as in Acorus.
In some species the leaves are very large, e.g. the simple leaves of Alocasia indica Schott, Xanthosoma maximiliani Schott, etc. or the decompound leaves of Amorphophalus and Dracontium. The leaf-blade is sagitate or ovate or even linear, attached to the petiole at the margin of the base or in some cases peltate. In Acorus the linear leaves are sessile.
The inflorescence is a spadix, the subtending spathe usually enclosing the spike sometimes in the primary stage only. Flowers are inconspicuous, crowded on the fleshy axis of spike, regular, hermaphrodite or unisexual and monoecious; excepting the spathe of the spadix no bract or bracteole is present. The axis of the spike may be wholly covered by flowers or the apical part is naked and is called the appendage.
Perianth absent but present in most hermaphrodite flowers in 2 trimerous or dimerous whorls; segments free or united. Stamens 6 in 2 whorls or 3 in 1 whorl and united to form a synandrium; often stamens only 2 or very rarely one only.
ADVERTISEMENTS:
The anthers dehisce by apical pores; the pollens are often in tetrads. Free or united staminodes may be present in female flowers. Ovary superior, one to many-locular, with few to many ovules in each cell; placentation parietal, marginal or axillary; stigma one or more; style absent. Fruit is a berry; seeds with or without endosperm.
Flowers are protogynous and entomophilous. The insects are attracted by the spathe and the appendage which are often coloured and also by the strong offensive odour emitted by some flowers.
The-spathe is constricted above the female flowers forming a chamber the mouth of which often closes at night; the inside of the spathe is often beset with hairs pointing downwards. The insect visiting the female flowers is thus prevented from coming out easily and pollinate the female flowers while moving- inside the spathial chamber.
The family contains about 1,500 species under 115 genera growing in the warmer countries of the world with only a few in the temperate regions. Most species prefer a humid condition while some grow in marshes and Pistia stratiotes Linn, is an aquatic weed floating in fresh-water lakes.
Economic Importance:
The tuberous rhizome and corms of most species contain plenty of starch and these are edible after boiling. Alocasia indie a (Roxb.) Schott. —the Man Kanda or Man Kachoo of eastern India, Colocasia esculenta (L.) Schott, the Kachoo, Arvi, or Ghuina, Amorphophalus campanalatus Blume the O1, Suran, Zamin- kanda, the Elephant’s foot, etc. are much cultivated for the purpose.
The leaf-blade and petiole of Xanthosoma maximiliani Schott. and some Amorphophalus and Colocasia are also used as vegetables. The fruiting spadix of Monstera deliciosa Liebm. is eaten as a fruit.
Some have medicinal value, e.g. Scindapsus, Ithaphidophora, Acorus calamus Linn, etc. Acorus calamus is the sweet-flag of commerce, the rhizome of which is sweet-scented and is used in perfumery. It is the Swet Bacha of the Indian Vaidas.
Anthurium, Caladium, Zantedeschia (Arum-Lily) are cultivated as ornamental plants. Some climbers like Monstera, Scindapsus and Rhaphidophora are also cultivated likewise and of the last two some having variegated leaves which are very popular in Indian gardens.
ADVERTISEMENTS:
Floral Range:
The spadix is usually very prominent with its spathe and the appendage of the spike. In the American genus Dracontium and the Indo-Malayan Amorphophallus it is often very large, about 2 mtr. in height, and the coloured spathe which looks like a funnel is over a metre across and so in height.
In most genera the spathe opens in the form of a funnel exposing the flowers; in other cases the spathe encloses the whole of the spike or only the lower part encloses the fertile part of the spike forming a chamber while the upper part is more or less a flat dorsiventral structure forming a back ground to the appendage.
The spathe is green in many genera but petaloid in others; Anthurium has a spathe which is brilliant scarlet, Zantedeschia has a white spathe. The spathe is often deciduous, e.g. Scindapsus, Rhaphidophora, Colocasia, etc., and persistent in others, e.g. Alocasia, Caladium, Typhonium, etc. In Acorus there is no spathe but the penduncle extends on one side from the base of the axis in the form of a spathe.
ADVERTISEMENTS:
The axis of the spadix is completely covered with flowers in Acorus, Calla, etc. or it is prolonged into a sterile appendage which may be coloured or green, and may be club-shaped, e.g. Amorphophallus campanulatus Bl., some species of Arisaema, etc., or it is very long, slender and thread-like as in Sauromatum, some Arisaema, etc.
Flowers are bisexual, as in Acorus, Calla, Anthurium, Monstera, etc. and unisexual in most other genera. Perianth usually present in bisexual flowers but absent in Calla, Monstera, etc. In Acorus there are 6 perianth segments in 2 whorls while those are 4 in 2 whorls in Anthurium and Gymnostachys.
Segments may be free as in Acorus or united as in Spathiphyllum. Stamens may be six as in Pothos, Acorus, etc. or less; in Typhonium there are 1-3 stamens, in Cryptocoryne (Lagenandra) 1-2 and in Arisarum and Biarum only one.
Gynoecium composed of 3 carpels in most genera but there is only one carpel in Pistia. Ovary may be 3-celled as in Pothos, Acorus, etc., or 1-celled as in Scindapsus, Lasia, etc.; 2-locular ovary as well as ovaries with more than 3 cells also occur.
Affinity:
Araceae appears to be closely related to Palmae, both the families having same type of inflorescence and inconspicuous hypogynous, regular flowers.
The 2 families have been included in the same order spadiciflorae by Rendle while Engler places them in 2 distinct orders, viz. Principes with single family Palmae and Spathiflorae to accommodate 2 families Araceae and Lemnaceae and the 2 orders are placed close to each other in his system.
Hutchinson considers that Palmae and Araceae are allied to each other both having been originated from Liliaceous stock in different lines. Takhta- jam and Cronquist also consider that Palmae and Araceae are close to each other. Araceae is again closely related to Lemnaceae which appears to have been derived from Araceae through the floating genus Pistia.
ADVERTISEMENTS:
Subdivisions of the family:
Engler divided the family into 8 subfamilies, viz.;
Sub. f. I Pothoideae:
Latex and raphides absent; flowers bisexual; perianth present, Pothos, Acorus, Anthurium, etc.
Sub. f. II Monsteroideae:
Latex absent, raphides present; flowers bisexual, without perianth. Monstera, Scindapsus, Rhaphidophora, etc.
ADVERTISEMENTS:
Sub. f. III Calloideae:
Latex present; flowers usually bisexual, perianthless. Calla and 3 other genera.
Sub. f. IV Lasioideae:
Latex present, raphides present; flowers hermaphrodite or unisexual, perianth present or absent; seeds usually without endosperm. Lasia, Amorphophallus, etc.
Sub f. V Philodendroideae:
Latex present, raphides present or absent; flowers unisexual and naked; seeds usually with endosperm; leaves parallel-nerved. Philodendron, Zantedeschia, etc.
Sub. f. VI Colocasioideae:
Latex and raphides present; flowers unisexual and naked; seed with or without endosperm; leaves with reticulate veination, usually sagittate. Colocasia, Alocasia, Caladium, etc.
Sub. f. VII Aroideae:
Latex present, raphides present; flowers unisexual, usually perianthless; seeds with endosperm; leaves reticulately veined. Arum, Spathicarfra, Arisarum, etc.
Sub. f. VIII Pistioideae:
Floating herb; latex and raphides absent; flowers unisexual, naked; seed with eindosperm. Single monotypic genus—Pistia.
Family # 2. Lemnaceae:
Lemnaceae are very small floating perennial herbs with a thalloid shoot which is dorsiventral and oblong or orbicular, or more or less hemispheric. In the former case, i.e. in Lemna and Spirodela a basal and an apical portion can be distinguished. The basal portion has 2 lateral pockets from which branches come out.
The branches may develop on both sides or on one side only so that the branching may be dichasial or helicoid. The branches are similar to the main plant body and are stalked. They may remain attached to the plant body or may get detached and behave like new plants.
According, to Hegelmaier the plant body is an undifferentiated thalloid shoot while according to Engler the apical portion represents a leaf and the basal portion is the stem. On the ventral surface one or more adventitious roots arise between the upper and lower portions. The apex of a root remains covered by a sheath at the beginning.
Wolffia and Wolffiela are rootless. The thallus-shoot is hemispheric or globose and a single branch or daughter shoot is developed at the back. Here the shoot is not differentiated into an upper or a lower portion.
The inflorescence is a small peduncled cyme in case of Lemna and Spirodela coming out from one of the pockets instead of a branch. In the early stage it remains covered by a minute scale comparable to the spathe in Araceae. Each inflorescence consists of a pair of male flowers and a female.
The flowers are without perianth. The male with a single stamen; the filament filiform or fusiform; anther 1-2-celled. The female flowet with a monocarpellary, stalked, flasked-shaped ovary with 1 or few basal, erect, orthotropous or anatropous ovules; style short, stigma funnel-shaped.
In Wolffia and Wolffiela a male and a female flower develop side by side on the dorsal flat surface of the plant body. The fruit is a capsule with circumscissile dehiscence or is a utricle; the seed with an outer fleshy and an inner delicate seed-coat and scanty endosperm surrounding a large cotyledon.
The flowers are protogynous and are pollinated by insects or often by the agency of water. The pollen grains are warty and get easily stuck to the funnel-shaped stigma that secretes a sugary fluid.
The family consists of about 27 species under 4 genera occurring in fresh water pools or marshes in all tropical and temperate countries. They are of no economic importance except that they serve as food for the fish. Wolffia arrhiza Wimm. is the smallest among the Angiosperms.
In tropical countries the plants flower regularly, while in temperate countries they seldom come to flower and the plants propagate by production of winter buds instead of vegetative buds. The winter buds lie dormant on the bottom of the pool or in the crevices on the sides and produce new plants at the advent of warmer period and come to the surface of water.
Affinity:
The family is closely related to Araceae and appear to have originated from Pistia of which it is probably a very reduced form as evidenced by morphological, anatomical and cytological studies. Lawalree, however (1945), holds altogether a different view.
According to him the presence of the minute scale in the pocket is a character common to the members of Helobieae as having the “squamulae intravaginalis” and states that Lemnaceae originated from that group.
