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In this article we will discuss about:- 1. Characters of Pontederiaceae 2. Distribution of Pontederiaceae 3. Economic Importance 4. Affinities.
Characters of Pontederiaceae:
Plants floating aquati herbs, leaves 1/2 alternate, with spongy inflated petiole; flowers hermaphrodite, hypogynous, zygomorphic; perianth petaloid, connate; stamens 6(3 + 3); carpels 3, syncarpous; fruit capsule or one seed achene.
A. Vegetative characters:
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Habit:
Aquatic, mostly perennial herbs, floating or rooting in subtrate.
Root:
Fibrous, root stock thick short or creeping.
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Stem:
Very short or erect and unbranched offsets stolons or rhizomes, mostly enveloped by sheathing leaf bases.
Leaf:
Simple, 1/2 alternate with sheathing bases and spongy inflated petiole sometimes completely reduced and the leaf is represented by a linear leaf-like flattened petiole.
B. Floral characters:
Inflorescence:
Raceme or panicle spike, subtended by spathe-like leaf sheath.
Flower:
Hermaphrodite, hypogynous, more or less zygomorphic, with subtending bracts.
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Perianth:
Tepals 6, in two whorls, (3+3), connate in a tube below, imbricate semi-persistent; rarely free; quite similar petal like, petaloid.
Androecium:
Stamens 6 or reduced to 3 or 1; inserted on perianth at different heights; filaments filiform somewhat unequal; anthers bithecous, introrse, dehiscing by pores or by longitudinal slits, filament slender.
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Gynoecium:
Carpels 3, syncorpous, superior; ovary trilocular, axile placentation ovules many or solitary and pendulous from each placenta; anatropous, style 1 long, strigma 1-6 lobed or 6-toothed or capitate.
Fruit:
Capsule or 1-seeded achene, 1-seeded utricle.
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Seed:
Ribbed lengthwise of furrowed, endosperm mealy and copious, embryo small, straight and linear.
Pollination:
Entomophilous; in some species flowers cleistogamous.
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Floral formulae:
Distribution of Pontederiaceae:
Pontederiaceae with 6 genera and 28 species is distributed in the tropical and subtropical zones of both the hemispheres Eichornia crassipes (water hyacinth) is the pest in the tanks.
Economic Importance of Pontederiaceae:
The family is not of much economic importance.
Ornamentals:
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Eichhornia, introduced as an ornamental, has become a serious weed clogging waterways and even impedes navigation and fishing in warm countries.
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Pontederia is grown to a limited extent as aquatic ornamental in pools.
Common plants of the family:
1. Eichhornia crassipes – Water hyacinth; floating herb.
2. Monochoria hastata – Robust aquatic herb with pale-blue flowers.
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3. Hydrothrix – Single stamen represents androecium.
Affinities of Pontederiaceae:
Pontederiaceae was placed in series 3rd, the Coronarieae next to Liliaceae by Bentham & Hooker. Later it was placed under Farinosae after Commelinaceae by Engler. Its affinity with Commelinaceae is established on account of mealy endosperm and small embryo, the variability and reduction in the androecium, and the floral zygomorphy.
Actually this family forms a link between Commetinales and Liliflorae. It resembles Liliaceae in the floral organisation except in the nature of endosperm. The family also recalls Aeroid affinity as seen from habit, structure of the inflorescence with spathe like bract.
It also bears some relationship with the members of the Helobieae as indicated in the similar mode of branching in both Eichhornia and Zosterct (Potamogetanaceae), helobial endosperm formation and aemoboid tapetum in some genera.
Division of the family & chief genera:
Tribe I. Eichhornieae:
Ovary with 3 fertile chambers, Capsule many seeded. Perianth members united in a tubular perigone. Stamens 6. Genus: I, Eichhornia with 5 species.
Tribe II. Heteranthereae:
Perigone spreading, wide; perianth member some-times very tender and soft, coloured; almost free to the base or very slightly connate; then stamens 6; or if perianth members are united in a tubular perigone then stamens 3 or 1. Genera: 3, Monochoria, Heteranthera and Hydrothrix.
Tribe III. Pontederiae:
Ovary with 1 fertile chamber, fruit dehiscent 1 seeded. Genera: 2. Pontederia and Reussia.
