Reproductive strategies, relichenization and thallus development observed in situ in leaf-dwelling lichen communities
Here we use the term ‘algae’ to refer to the broad, polyphyletic assemblage of photosynthetic life forms exclusive of the embryophytes, as do contemporary phycology textbooks. Almost all algae found in lichen associations are either green (chlorophytes) or blue-green (cyanophytes/cyanobacteria); two lichens with heterokontophyte algal symbionts are also known ( Tschermak-Woess, 1988 ). The widely used term ‘phycobiont’ is applied to all these algal symbionts.
Author for correspondence: William B. Sanders Tel: +34 91 7452500 ext. 274 Fax: +34 91 5640800 Email: email@example.com
- • Suppositions about lichen reproductive strategies were investigated and elusive early stages of lichen ontogeny documented in a foliicolous lichen community.
- • Plastic coverslips attached to supportive netting were placed among foliicolous lichen communities within a neotropical lowland forest. The germination and development of diverse lichen propagules colonizing the coverslips were studied with light microscopy.
- • Foliicolous lichens were observed to begin development from lichenized vegetative propagules, aposymbiotic fungal spores, fungal spores dispersed together with attached phycobionts, and diahyphae. Aposymbiotically dispersed spores and diahyphae were capable of associating with compatible phycobionts encountered upon the substratum, following germination.
- • Many developing thalli produced characteristic structures (discoid isidia, thalline setae, pycnidia, etc.) which permitted their recognition as typical members of the foliicolous lichen community. Thalline setae in Tricharia were produced upon the prothallus, and subsequently incorporated into the thallus proper by advance of the lichenized thallus margin. Tricharia and other members of the Gomphillaceae showed a distinctive organization of symbionts in thallus growth, whereby the unicellular green phycobiont cells were positioned at the tips of advancing fascicles of mycobiont hyphae. In Coenogonium sp., branching filaments of the phycobiont Trentepohlia grew along prothallic paths initiated by the mycobiont.