Pteridophytes

 

Marsilea

 

Habit of Marsilea:

The plants are herbaceous with rhizomatous stem, creeping on or just below the soil surface.

The species of Marsilea are generally aqua­tic or amphibious in nature with their roots embedded in mud or damp soil. The aquatic species — M. minuta and M. quadrifolia — occur in fresh water ponds, shallow water, or in mud or damp soil.

 

Structure of Marsilea:

Sporophyte:

The sporophytic plant body of Marsilea shows differentiation of stem, leaves and roots (Fig. 7.116).

1. Stem:

The stem is long, slender and freely-branched rhizome of indefinite growth that grows on or just below the soil surface. It is differentiated into nodes and internodes. The internodes are gene­rally long in aquatic species but are short in sub- terrestrial or terrestrial species. The production of underground tubers on rhizome has been repor­ted only in M. hirsuta.

The outermost layer is epidermis, composed of compactly arranged thick-walled cells and are devoid of stomata. The cortex is extensive and differentiated into three layers viz., outer cortex, middle cortex, and inner cortex. The outer cor­tex is parenchymatous with large air spaces.

The air chambers are separated from each other by a single-layered septum. The middle cortex is scle­renchymatous, while the inner cortex is made up of compactly arranged parenchymatous cells. The air spaces are absent in xerophytic species (e.g., M. aegyptiaca).

The stele is amphiphloic solenostelic which occupies the centre of the rhizome. Xylem occurs in the form of a ring and is surrounded on either side by phloem.

The central part of the stele is occupied by pith which is parenchymatous in aquatic species and sclerenchymatous in xerophytic species (e.g., M. aegyptiaca). The stele is bounded externally by outer pericycle and outer endodermis, while it is bounded inter­nally by inner pericycle and inner endodermis.

Reproduction in Marsilea:

Marsilea reproduces vegetatively as well as by means of the spores.

 

i. Vegetative Reproduction:

 

Under some unfavourable circumstances the subterranean branches of the rhizome form tubers. These structures have reserve food in the form of oil globules which help them to over­come the unfavourable conditions. On return of the favourable conditions, these tubers germi­nate and form new plant body (e.g., M. hirsuta, M. minuta, M. erosa).