Trabeculae are the modified endodermal cells in the stem of Selaginella. These radially elongated structures with Casparian strips suspend the central stele within the air-filled cortical cavity.

Question Solution

The correct answer is Trabeculae. In Selaginella stems, trabeculae form by radial elongation of endodermal cells, connecting cortex to stele and aiding structural support in aerated tissues.

Option Analysis

• Glossopodium: Incorrect. This is a specialized, leaf-like structure at the rhizophore apex in some Selaginella species, functioning in root transition, not stem endodermis modification.​

• Trabeculae: Correct. Modified endodermal cells that are tubular, unicellular, and bear Casparian strips; they span the air spaces, anchoring the vascular stele centrally.

• Rhizophore: Incorrect. A unique, dichotomously branching organ bearing roots at tips; it resembles roots internally but originates from stem-forking, unrelated to endodermal modification.​

• Ligule: Incorrect. A small, flap-like outgrowth on the upper surface of young leaves (sporophylls and trophophylls), aiding water retention; purely foliar, not stem endodermal.​

Introduction to Modified Endodermal Cells in Selaginella

Modified endodermal cells in the Selaginella stem, known as trabeculae, provide critical support in this pteridophyte’s aerated tissues. These structures highlight Selaginella’s adaptation to moist habitats through specialized anatomy. Botany exams often test this unique feature.

Trabeculae Structure and Function

Trabeculae arise from radially elongated endodermal cells forming tubular bridges across cortical air spaces. They retain Casparian strips for selective transport and mechanically suspend the protostele, preventing collapse in hollow stems.

Distinguishing Other Features

• Glossopodium serves as a root-primordia at rhizophore tips.

• Rhizophore acts as a root-bearing stem organ.

• Ligule protects developing leaves.
  Only trabeculae represent endodermal modification in Selaginella stems.​

Significance in Pteridophytes

These cells exemplify evolutionary adaptations for vascular efficiency in lycophytes, aiding water relations and mechanical stability without secondary growth.