In this article we will discuss about the anatomy of marsilea with the help of diagrams.
Occasionally, the same species may be found to grow in water as well as on land and consequently land form and water form are known to occur in the genus. Land and water forms can be easily distinguished on morphological grounds. Land forms (Fig. 10.11) have short internodes, branched roots, a few air spaces and more sclerenchyma in vegetative organs.
The leaves have long petioles and stomata are distributed on both the surfaces of leaflets. Water forms, in contrast, have long internodes, un-branched roots and flexible petiole. There is practically no sclerenchyma in vegetative organs and there are extensive air spaces. Stomata are restricted largely to upper surface of leaflets.
Rhizome in Marsilea grows by means of an apical cell, with three cutting faces. The vascular cylinder is an amphiphloic siphonostele (solenostele). The xylem cylinder is surrounded externally as well as internally by endodermis, pericycle, and phloem (Fig. 10.8B, C). The maturation pattern of xylem is mesarch. Some species, however, have conspicuous protoxylem masses that are exarch.
In land forms the inner cortex and pith are sclerotic whereas in water forms these zones are uniformly parenchymatous. Middle cortex is aerenchymatous with a single ring of air chambers. The air chambers are separated from one another by one layered septum.
Aerenchyma is more extensive in water forms and less extensive in land forms. The outer cortex is parenchymatous, one to several cells in thickness. Lying scattered in the outer and inner cortical zones are some tannin cells.
The stele of petiole (Fig. 10.8 D) is nearly triangular and is bound by single endodermis. There are two arms of xylem which are curved away, from each other, on adaxial side and are relatively close on the abaxial side. Each xylem arm comprises one or two metaxylem elements in centre and a few protoxylem elements at both ends. The cortex is similar to that of stem and is variable in land and water forms.
Root meristem consists of an apical cell with 3 cutting faces. The cortex of the root also has aerenchyma. It is extensive in water forms. The roots are diarch and exarch (Fig. 10.8E). In the centre are two metaxylem elements and there are two groups of protoxylem elements on the periphery. There are reports of vessels in several species of Marsilea. In two species, M. drummondii and M. alata vessels occur in root, petiole as well as rhizome.