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Observe the external features of the plant, and arrangement, types and shape of leaf, ligule, rhizophore and roots.
1. Plant body is sporophytic and the sporophyte is evergreen and perennial.
2. Most of the species are prostrate but Selaginella trachyphylla is sub-erect and S.erythropus is erect (Fig. 208).
3. Size of the sporophyte ranges from few centimetres to several feet in different species.
4. Plant body is differentiated into stem, leaves, rhizophore and roots.
5. Two sub-genera, namely Heterophyllum and Homoeophyllum, have been recognized in the genus Selaginella on the basis of characters of stem and leaves.
6. In sub-genus Heterophyllum the stem is prostrate, dorsiventral with lateral branching. It contains two types of leaves. But in case of sub-genus Homoeophyllum the stem is somewhat erect showing dichotomous type of branching and all the leaves are of only one type.
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7. Leaves are simple, small, thin and ovate to lanceolate in shape (Fig. 210).
8. Each leaf contains a midrib.
9. In most of the species, leaves are of two types, i.e., smaller and larger (Fig. 209).
10. Leaves are arranged on the stem in four longitudinal rows.
11. Two rows of smaller leaves are present on the dorsal surface of stem while remaining two rows of larger leaves (Fig. 211) on the ventral surface.
12. A pair of leaves comprises of a small leaf on the dorsal surface and a large leaf on the ventral surface of the stem.
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13. At the base of upper or adaxial surface of each leaf is present a thin membranous finger-like structure called ligule (Figs. 210,212).
14. Each ligule (Fig. 212) consists of a basal hemispherical glossopodium made up of large thin-walled cells and surrounded by a glossopodial sheath. Above the glossopodium is the body of ligule made up of many small and large cells.
15. At the place of branching in stem, arises a long, unbranched, leafless structure towards the lower side. This is known as rhizophore (Figs. 209,211).
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16. Rhizophore becomes branched at its tip and forms many adventitious roots.
