Structure and in situ development of the microlichen Gyalectidium paolae (Gomphillaceae, Ascomycota), an overlooked colonist on palm leaves in southwest Florida

• Published in: American journal of botany 2015-09, Vol.102 (9), p.1403-1412
• Main Authors: Sanders, William B., de los Ríos, Asunción
• Format: Article
• Language: English
• Subjects: Arecaceae - microbiology; Arecaceae - physiology; Ascomycota; Ascomycota - cytology; Ascomycota - growth & development; Ascomycota - physiology; Ascomycota - ultrastructure; Botany; diahyphae; Florida; foliicolous lichen; hyphophore; Leaves; Lichens; Lichens - cytology; Lichens - growth & development; Lichens - physiology; Lichens - ultrastructure; Microscopy; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; Plant Leaves - microbiology; Plant Leaves - physiology; Symbiosis; Trees
• ISSN: 0002-9122; 1537-2197
• DOI: 10.3732/ajb.1500202

PREMISE OF THE STUDY: Nondeciduous leaves of warm, humid climates can host highly specialized communities of diminutive lichens. The rarely reported Gyalectidium paolae, locally abundant on palm leaves in southwest Florida, may reproduce when as small as 0.15 mm diameter. We examined structural and developmental features to better understand the lifestyle of this extreme ephemeral. METHODS: Blocks containing resin-embedded thalii were sectioned and examined with TEM and SEM-BSE. Propagule development was studied with light microscopy applied to inoculated and naturally colonized plastic coverslips placed in the field. KEY RESULTS: Thallus areolae showed a heterogeneous covering that varied from cellular cortex to a simpler structure derived from fungal wall materials and sparse fungal cells of reduced diameter. Plates of crystalline deposits seemed to interrupt thallus structure, elevating the surface layer. No organized algal layer was present. Symbiont interactions were limited to appositional wall contacts with no haustorial penetration observed. Symbiotic propagules germinated promptly, but relative growth of fungal vs. algal components varied considerably. Smaller photobiont cells released from sporangia were present at the periphery of the thallus, or escaped to some distance. Fully formed hyphophores with abundant propagules appeared within 5 months, although there was evidence that propagule formation in Gyalectidium might occur much sooner. CONCLUSIONS: Gyalectidium paolae builds relatively simple thalii with limited fungal structure, prioritizing rapid formation of asexual propagules. Codispersal of algal symbionts permitted propagules to develop directly into thalii, but microenvironmental conditions may strongly influence survival and developmental equilibrium between the two symbionts necessary for success as a lichen.