Velamen
/vəˈleɪmən/
Definition
Velamen is the spongy, multilayered outer covering on the aerial roots of many epiphytic orchids and some aroids. Made of dead cells, it differs from the living root tissues beneath it. It rapidly absorbs and holds water and dissolved minerals, slows water loss, and helps protect the root from drying and intense light. When dry it often looks white or silvery, turning greener when wet as inner tissues show through.
Function in Plants
- Water capture during brief wetting: In many epiphytic orchids, velamen helps roots take up rain, dew, and mist quickly, which suits plants that dry fast between wet periods.
- Protection for exposed roots: The layered covering reduces physical stress on aerial roots and can limit rapid water loss after the surface dries, helping roots cope with bright, airy conditions.
- Visual cue for root condition: Growers often watch its color change. It commonly looks silvery or white when dry and greener when wet, because the tissues beneath become more visible.
- Useful in plant identification: Its presence is characteristic of many orchid roots and some aroids, so it can help distinguish root adaptations linked to life on bark, rock, or other fast-draining surfaces.
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