Comparative morphology and fine structure of a group of Umbilicaria lichens

Abstract

The gross morphology and fine structure of tissue layers in five Umbilicaria species (U. vellea, U. mammulata, U. papulosa, U. muhlenbergii, and U. deusta) were examined using bright-field and transmission electron microscopy. Differences in the surface topography of the upper and lower cortexes of the five species were found. Four of the species contained an osmiophilic banding material on the walls of the outermost file of living upper cortical hyphae. Although the fine structure of phycobiont cells was basically similar for all species, U. vellea was found to have smaller amounts of stored starch and peripheral lipid in cells of the algal zone than the other four species. Algal–fungal contacts were not haustorial, although aplanospore clusters were penetrated by wedge-shaped intrusive hyphae. Senescent algal cells accumulated large numbers of starch grains. Hyphae in the medullary zones were found to be similar for all species with the exception of U. muhlenbergii, which had an extrahyphal, gel-like matrix. Extensive, sheetlike lamellae were also present in the lower cortex of this species. It would appear that many aspects of thallus fine structure and morphology have a direct effect on gas exchange and water relations responses previously reported in the literature.

THE EFFECT OF WINTER FIELD CONDITIONS ON THE DISTRIBUTION OF TWO SPECIES OF UMBILICARIA

“…The thallus margins and portions of the tissue within 2 mm of the umbilicus were discarded in order to minimize variance as a result of possible differences in age of diflFerent regions of the thallus (Larson, 1983). Strips were cut into 1 mm^ blocks and fixed as described by Scott & Larson (1984).…”

“…This study presents quantified fine structural data about thalli whose gas exchange potential has already been documented. Two earlier publications (Scott & Larson, 1984, 1985 concerning mechanisms which influence species distribution in Umbilicaria spp., provided evidence that Umbilicaria vellea had a significantly depressed net photosynthetic potential (0-08 mg COj g d.wf^ h~^) following six months of transplantation to the snow-covered habitat of Umbilicaria deusta. U. deusta was unaffected by overwintering in the steeply-inclined, snow-free U. vellea habitat.…”

THE EFFECT OF WINTER FIELD CONDITIONS ON THE DISTRIBUTION OF TWO SPECIES OF UMBILICARIA

“…Accumulations of respiratory substrate would not normally be necessary. In addition, the large amount of respiring fungal tissue (thick upper and lower cortices, large umbilicus, closely-packed medullary zone) (Scott & Larson, 1984) would necessitate a greater conversion of starch and algal polyols to ribitol and mannitol (fungal polyol) in order to naaintain the mycobiont partner. Translocation of photosynthetically fixed carbon may be more rapid in U. vellea allowing thalli to photosynthesize throughout the year.…”

“…A great deal of energy in terms of fixed carbon would be allocated to the storage pool in order to permit the plant to tolerate the period when there is no opportunity for photosynthesis. In addition, the isidiate nature of U. deusta would result in a concentration of algal growth towards the upper external surfaces (Scott & Larson, 1984) and would limit the resources available for increase in diameter and for proliferation of fungal tissue.…”

“…Despite a very real need, this process has been infrequently applied to studies of the ecology of lichens. However, such an 0028-646X/86/020327 +17 $03.00 © 1986 The New Phytologist approach was adopted in a research programme which has been described in Scott & Larson (1984, 1985a and which is concluded in this paper. In previous work (Scott & Larson 1984, 1985 evidence was provided that Umbilicaria vellea (L.) Ach.…”