AP BIOLOGY

Detailed explanation-1: -They resemble mosses and may be frequently overlooked. Selaginella apoda has dimorphic leaves arranged in four ranks. The leaves of the lateral ranks are larger than those of the upper and lower ranks. Like other spike-mosses, the reproductive structure is a leafy, spore cone borne at the apex of the stem.

Detailed explanation-2: -The endodermis in Selaginella is unique and its cells are called trabeculae. These cells are highly elongated and span an air space which intervenes between the cortex and the stele.

Detailed explanation-3: -The stem of Selaginella is formed of vascular stele which is protostele. Xylem is present in the center and is surrounded by phloem and phloem is surrounded by pericycle. Pith is absent. Trabeculae are present which are tube liked structures and are modified endodermal cells with casparian strips.

Detailed explanation-4: -The endodermis in Selaginella except in xerophytic species (S. lepidophylla and S. rupestris) is interrupted by large intercellular spaces. This is called the trabeculated endodermis.