Outer covering of epiphytic root is

The correct option is Velamen.

Detailed Explanation:
Epiphytes are plants that grow on other plants for structural support rather than nutrition. Because their roots are suspended in the air (aerial roots) rather than anchored in the soil, they require special adaptations to absorb moisture and nutrients from the environment.
The outer covering of these epiphytic roots is made of a specialized, multi-layered tissue called the velamen.

Function and Features of Velamen:
1. Sponge-like Absorption: Velamen consists of dead, hollow cells with thickened walls that act like a sponge. It absorbs moisture, rain, and dew directly from the atmosphere.
2. Protection against Desiccation: When dry, the cells fill with air, helping to reflect light and reduce water loss from the internal tissues of the root.
3. Photosynthesis support: When wet, the velamen becomes transparent, allowing the underlying green chloroplast-containing cells of the root to perform photosynthesis.

Analysis of Other Options:
- Rhizophore: A leafless, root-like structure found in certain primitive vascular plants like Selaginella that grows downwards to produce true roots upon contact with the soil.
- Osmophore: A scent-producing gland in flowers that releases volatile essential oils to attract insect pollinators.
- Pneumatophore: A specialized aerial root (breathing root) found in mangrove plants that grows upwards out of the waterlogged, oxygen-depleted soil to facilitate respiration.