Collema dichotomum (river jelly lichen)

Collema dichotomum, the river jelly lichen is rare amphibious fungus growing on siliceous rocks in cool and clean streams.

The dry lichen is very brittle but turns into a jelly like texture when wet. 

Collema dichotomum demands on its environment make it an indicator of the ecological health of streams. Many European populations of this lichen have declined and it is confronted with threats from multiple sources.

Species detail

The river jelly lichen produces 

  • small rosettes up to 2.5cm in diameter
  • Thalli are 
    • greyish dark green to almost brownish when dry 
    • dark to bright green (sometimes with a brownish tinge) when wet
  • more or less dichotomous branching pattern
  • convex lobes with the disc-like reddish brown fruiting bodies (apothecia) on the upper surface of the thalllus
  • Collema dichotomum - close up of the typical dichotomous branching pattern
    Taxonomy

    Find out about the appearance and structure of the river jelly lichen in comparison with other jelly lichen species. Learn the basionym and synonyms for this species.

  • Dry river jelly lichen
    Distribution and habitat

    Discover where the river jelly lichen is found and the types of habitat it typically grows in.

  • Collema dichotomum
    Biology

    Learn about the need for Collema dichotomum to have a compatible algal partner and find out why poorly developed apothecia, common in the southern range of the species, is raising concern.

  • Collema dichotomum - fruiting body close up
    Conservation

    Populations of the river jelly lichen have declined in many parts of its European distribution range. Discover the current and potential threats to the survival of this species and find out what can be done to contirbute to a better understanding of its distribution.

  • Collemadichotomum - fruiting bodies and typical dichomous branching pattern of thallus.
    References

    Get reference material for Collema dichotomum.

Images

Wet river jelly lichen

Wet river jelly lichen

Collema dichotomum - close up of the typical dichotomous branching pattern

Collema dichotomum - close up of the typical dichotomous branching pattern.

Dry river jelly lichen

Dry river jelly lichen

Collema dichotomum - section of thallus

Collema dichotomum - section of thallus showing medulla in centre and cyanobacteria layers below the upper and lower surface.

Collema dichotomum - fruiting body close up

Collema dichotomum - fruiting body close up.

Collemadichotomum - fruiting bodies and typical dichomous branching pattern of thallus

Collemadichotomum - fruiting bodies and typical dichomous branching pattern of thallus.

Basionym

Tremella dichotomum Withering 1776

Synonyms

Collema cataclysum Koerber 1855

Collema fluviatile (Huds.) Steudel 1824

Collemodium cataclystum (Koerb.) Nyl 1879

Enchylium fluviatile (Huds.)

Leptogium cataclystum (Koerber) Harm. 1905

Leptogium fluviatile (Huds.) Leighton

Leptogium rivulare auct. britt. non (Ach.) Montagne

Lichen fluviatilis Huds. 1778

About the author

Holger Thüs
Dr Holger Thus

Lichen curator investigating the ecology and evolution of amphibious lichens, bioindication and the conservation of crytpogamic plants.

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