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In this article we will discuss about the Classification of Pandanales. According to Engler and Prantl, Pandanales consists of three families:- 1. Typhaceae 2. Sparganiaceae 3. Pandanaceae.
Family # 1. Typhaceae:
Typhaceae are aquatic herbs growing in fresh water or in marshes, with a long creeping rhizome and erect simple shoots arising from the axils of lateral scales of the rhizome. Leaves are distichous, mostly near the base; long and linear or strap-shaped, entire, obtuse at apex and sheathing at the base, rather thick and spongy; lower leaves reduced to long sheaths only.
Flowers are monoecious, very small and numerous, crowded in terminal spadix, the males above and the females below, the 2 portions contiguous or remote from each other; 2 alternate deciduous bracts are present, one at the base of the female portion of the spadix and the other at the base of the male portion and a few more smaller bracts often found in between the male flowers.
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The axis of the spadix is more or less compressed. The female flowers are mostly borne on short cylindrical outgrowths while the male flowers are produced directly on the axis. Flowers are anemophilous. Perianth is represented by very slender jointed threads or elongated spatulate scales, or these may be altogether absent.
The number of stamens in a male flower is usually three but it may be less or upto 5; filaments free or united at base; anthers linear basifixed, with connective produced above; the pollen grains are often united in tetrad. Rudimentary ovary is often present in male flowers. A normal female flower has a long gynophore bearing many long simple hairs.
Often these flowers are subtended by small spathulate scale-like bracts. The hairs are persistent and elongate in fruit in the dispersal of which they are very helpful. The small ovary is fusiform, unilocular, narrowed into the style with a ligulate or unilateral stigma; ovule solitary, pendulous and anatropous.
Fruit is a small nutlet, ultimately splitting. The seed with a striate testa contains a fleshy or mealy endosperm and a narrow, straight, elongated embryo.
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Floral formula:
This is a monotypic family containing a single genus Typha with about 15 species distributed in temperate and tropical countries of the world. In India T. elephantina Roxb. and T. angustata Chaub. & Bory are the 2 species growing in fresh water marshes in the plains. The long leaves of these 2 species (the Bull rush) are woven into mats and are used in thatching.
Typhaceae is closely allied to Sparganiaceae both having simple unisexual flowers, superior unilocular ovary and solitary pendulous anatropous ovule. Plants of both the families grow in similar aquatic situation. Engler and Rendle consider that Typhaceae and Sparganiaceae are closely allied to each other and also to Pandanaceae which also have plants with simple unisexual flowers.
The ovary is superior and unilocular and ovules are anatropous. They further consider that the 3 families are most primitive among the Monocotyledons and place them in the beginning of the Monocots under a single order Pandanales. Hutchinson and most other modern botanists are of the opinion that the simplicity of the flowers is the result of reduction and not due to primitiveness.
They further split the order Pandanales of Engler to Typhales with 2 families Typhaceae and Sparganiaceae and Pandanales with the single family Pandanaceae.
In Pandanaceae the dioecious plants have sporophylls usually numerous in the flowers, ovules 1-many in each carpel, oily endosperm and small embryo in the seed clearly indicate that the family is not so closely related to Typhaceae and Sparganiaceae and the removal of these 2 families from Pandanales to a separate order as Typhales by Hutchinson seems to be justified.
Pandanaceae appears to resemble the Palms and Cyclanthaceae to some extent while Typhaceae has some similarity with Araceae.
Family # 2. Sparganiaceae:
Sparganiaceae are rhizomatous aquatic herbs. Leaves are alternate, linear, stiff and erect or flaccid and floating, sheathing at the base. Flowers monoecious, anemophilous, crowded in male or female globose heads forming a paniculate inflorescence, the male heads occupying the upper part and the female heads the basal part. Perianth represented by a few membranous scales.
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Male flowers with 3 or more stamens, free or united; anthers oblong or cuneate, basifixed, dehiscing longitudinally. Female flower with a superior l-locular ovary; ovule solitary pendulous; style simple or forked with unilateral stigma. Fruit drupacious with a spongy exocarp and hard endocarp. Seed with a thin testa, a straight embryo and mealy endosperm.
Sparganiaceae is a unigeneric family with about 20 species but they are wide in their distribution in the temperate and frigid zones of both hemispheres. In India it is represented by S. simplex Huds. which is found in the Himalayas and Khasi hills at 2000 mtr. and above.
Family # 3. Pandanaceae:
Pandanaceae are the plants of this family are shrubs or short trees, rarely root-climbers. A full grown plant usually rests on a cluster of stilt-roots which come out from the basal part of the stem as well as the older branches as the main roots and often the lower part of the stem get decayed.
The leaves are long and leathery, densely whorled near the apex of the stem and branches or they are in 1/8 alternate phyllotaxy; sheathing at the base and usually keeled; keel and margins spinulose.
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The plants are dioecious with numerous small flowers. The male flowers are in simple or compound spadix. The lower bracts are foliacious and the upper are smaller and spathe-like and often showy. In Freycinetia bracts form an involucre, the inner being coloured. In Sararanga scale-like bracteoles are present.
The male flowers usually consist of several stamens, free or united and perianthless. In Sararanga a short obscurely lobed perianth is present. In Pandanus the stamens are arranged in the form of a spike or umbel on the floral axis, or there may be a single stamen only. The anthers are basifixed, 2- locular or rarely 4-locular and split lengthwise. The numerous stamens in Freycinetia surround a rudimentary ovary.
The female flowers are crowded in dense globular heads or cylindrical spikes which form a cluster in Freycinetia due to the shortening of the axis of inflorescence. In Sararanga it forms a pendulous panicle. In Pandanus and Freycinetia perianth is altogether absent in pistillate flower. In Sararanga a ring of undulate marginard perianth is present as in the male flower.
The gynoecium is superior and composed of one or few coherent carpels, a large number (70-80) in Sararanga, each unilocular and with sessile or sub sessile stigma, ovule solitary and basal or several in a row on the ventral suture, anatropous; a ring of staminodes surrounds the base of the pistil in Freycinetia.
The fruit is a syncarp of berries or drupes; in Pandanus the endocarp is hard and the mesocarp is fleshy, fibrous or woody. The seed is small and has a fleshy or oily endosperm and minute embryo.
Floral formula:
The family consists of 3 genera and over 250 species distributed in the tropical and subtropical regions of the old world from the sea-shore to about 1500 mtr in the hills in damp situations. It is represented in India by several species of Pandanus of which P. tectorius Sol. ex. Park (Syn. P. fascicularis Lam.) has sweet scented male flowers from which keora-water is manufactured.
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The family Pandanaceae lias been included in Pandanales by Engler along with Typhaceae and Sparganiaeeae, all having perianthless, unisexual flowers and superior ovary. Pandanaceae differs from the other two in habit and being dioecious, while Typhaceae and Sparganiaeeae are monoecious.
Engler as well as Rendle consider that the 3 families having simple flowers are the most primitive families among the Monocots and place the order Pandanales at the beginning of that class.
Hutchinson and most other modern taxonomists believe that the simplicity is not due to primitiveness but due to reduction and the 3 families are not so closely related as to be included in a single order and therefore remove Typhaceae and Sparganiaceae from Pandanales and place them in a distinct order Typhales.
Hutchinson considers that the 2 orders Typhales and Pandanales originated from Liliaceous stock in separate lines.
