Lobaria Pulmonaria - Reproduction

Reproduction

L. pulmonaria has the ability to form both vegetative propagation and sexual propagules at an age of about 25 years. In sexual reproduction, the species produces small reddish-brown discs known as apothecia containing asci, from which spores are forcibly released into the air (like ballistospores). Based on studies of ascospore germination, it has been suggested that L. pulmonaria spores use some mechanism to inhibit germination—the inhibition is lifted when the spores are grown in a synthetic growth medium containing an adsorbent like bovine serum albumin or α-cyclodextrin.

Dispersal by vegetative propagules (via soredia or isidia) has been determined as the predominant mode of reproduction in L. pulmonaria. In this method, the protruding propagules become dry and brittle during the regular wet/dry cycles of the lichen, and can easily crumble off the thallus. These fragments may develop into new thalli, either at the same locale or at a new site after dispersal by wind or rain. A number of steps are required for the development of the vegetative propagules, including the degeneration of the thallus cortex, replication of green algal cells, and entanglement of fungal hyphae with the green algal cells. This steps lead to an increase in internal pressure which eventually breaks through the cortex. Continued growth leads to these granules being pushed upwards and out of the thallus surface.