Short Notes on Podostemaceae | Dicotyledonae

The below mentioned article provides a short notes on Podostemonales.

Family Podostemaceae:

Podostemaceae is a submerged aquatic plants growing on rocky substratum under running water; the vegetative body of Podostemaceae is a flat and dorsiventral structure, thallus like in appearance or filamentous, sometimes slender and threadlike. Leaves of Podostemaceae are very small and scaly or moss ­like, often linear or subulate, rarely broader and dissected.

Flowers of Podostemaceae are solitary and termi­nal on short secondary shoots or many in cymose inflorescence; very small and bisexual; bracts and in case of solitary flowers a spathe is often present; pedicels usually long and slender.

Perianth of 3-5 segments in one whorl; segments free or more or less’ united; sometimes perianth-segments are many and scale-like or may be altogether absent and in such cases a membranous structure encloses the flower-bud.

Stamens many, in one or more whorls, free or the filaments united, often forming a tubular sheath; anthers introrse, dehiscing longitudinally by lateral slits; pollens in diads or tetrads.

Ovary superior, of 3-2 carpels, 3-1-celled; styles as many as carpels, stigma fimbriate; ovules many, anatropous, on axile or in unicellular ovary on free central placentas. Fruit a capsule with many minute seeds which have a mucilaginous covering, thick cotyledons and no endosperm.

The seed on germination gives rise to a very short primary axis but no primary root. From the primary axis rises the creeping thalloid or filamentous body endogenously.

This flat thalloid body is more root-like than stem, having a root-cap at the tip and branching endogenously or exogenously. It also produces the haptera or the fixing organs exogenously from the surface tissue. The branches or the secondary shoots produce leaves and bear the flowers.

Anatomy of the vegetative body shows that the vascular bundles are closed and collateral and usually scattered. The xylem is very much reduced but the phloem L well developed with large sieve tubes. The plants of this family show a considerable range of variation in vegetative as well as floral characters.

In some Podostemon the vegetative body is thread-like and in Dicraea it is flat and dorsiventral. In Mourera the main body is like a creeping rhizome bearing rather large leaves with a distinct petiole and much dissected lamina; the petiole sheathing at the base which remains attached to the shoot while the blade falls away.

Hydrobryum has an exogenously developed main body which is flat and much- branched and is not root-like in character. In this case the secondary shoots are also exo­genously developed and bear densely close small leaves giving the plant a moss-like appearance. The root-like body performs the work of photosynthesis. In some Dicraea there are short floating roots in addition to the hapteras.

Flowers of Dicraea are sessile while in Tristicha and others they are pedicelled. Spathela is present in the flowers of Dicraea, Mourera, Podostemon, etc. In Lacis monadelpha Bong, there are many stamens the filaments of which unite to form a tubular sheath round the ovary.

The embryo-sac development is of bisporic 4-nucleate type. In the final stage there is one synergid, an egg-cell and 2-closely lying antipodal cells. Some of the nucellus cells break down forming a cavity which contains some free nuclei. This cavity is known as pseudoembryosac and is a peculiar structure.

The family with 43 genera and about 150 species is distributed over the tropical and temperate regions of the world.

It is represented in India by several Species of Podostemon, Dicraea, Terniola and Hydrobryum. Podostemaceae is allied to Crassulaceae, Saxifragaceae and Rosaceae as shown by Rendle, Hutchinson, Takhtajan and Cronquist. P. Maheshwari proved from embryological study that Podostemaceae and Crassulaceae are closely related.

The family Hydrostachyaceae which is placed in the same order with Podostemaceae by Rendle and Hutchinson is not at all closely related according to the opinion of most authors.