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HEAVILY LICHENIZED PHYSOLINUM (CHLOROPHYTA) FROM A DIMLY LIT CAVE IN MISSOURI 1
Author(s) -
Davis Joseph S.,
Rands David G.,
Lachapelle Mario
Publication year - 1989
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.1529-8817.1989.tb00246.x
Subject(s) - biology , thallus , middle lamella , botany , chloroplast , ultrastructure , conidium , hypha , chlorophyta , plasmodesma , cell wall , algae , gene , biochemistry
Heavily lichenized Physolinum monile (De Wildem.) Printz from damp limestone walls in a dimly lit cave located in Missouri was studied from fresh collections and specimens fixed in situ, and from cultures. The narrow (7‐13 μm wide thallus), profusely branched plant consisted of filaments of the alga P. monile ensheathed by clear fungal cells (5‐8 in a single layer) that adhered tightly to each other and completely covered the algal cells. Cells of P. monile filaments were uninucleate, each containing a single massive chloroplast with numerous tightly packed thylakoids and lipid droplets and surrounded by a thin layer of cytoplasm. No plasmodesmata occurred in the cellulosic crosswalls between adjacent cells. The ensheathing fungal cells contained concentric bodies, produced haustoria that penetrated the algal cells, and developed hyphae (the tips of which formed clusters of conidia). Ensheathing fungal cells were well situated and constructed to concentrate light on the algal cells. Colonies of blue‐green algae were firmly attached to the surface of the fungal cells. The association was slow growing but frequently produced and released aplanospores from the algal cells. Aplanospores were single (not attached to each other) with smooth walls or united in groups of two or more. Structures resembling lichen soredia, composed of aplanospore‐like cells attached to one or more comdia‐like cells, commonly occurred among the lichenized Physolinum filaments. The single chloroplast that occupies most of the cell's volume, the numerous, tightly packed thylakoids, and light focusing by ensheathing fungus cells may enable the organism to survive in a dimly lit environment. Because the filamentous alga reproduces only by aplanospores, we propose resurrection of the genus Physolinum. The lichenized Physolinum somewhat resembles the lichens Coenogonium moniliforme Tuck. and Cystocoleus Thwaites.