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Growth from the Centre in an Umbilicate Lichen

Published online by Cambridge University Press:  28 March 2007

Geir Hestmark
Affiliation:
Division of Botany and Plant Physiology, Department of Biology, University of Oslo, P.O. Box 1066, N-0316 Oslo, Norway

Abstract

The pustules on the surface of the umbilicate lichen Lasallia pustulata are moved away from the centre and towards the thallus margins with an average speed of 1.8 mm per year, revealing a growth pattern organized radially and flowing from the centre of the thallus. Pustules close to the margin move substantially faster than those close to the centre; for each 10 mm added to the initial distance from the centre, the speed of outward movement is about doubled. This suggests that intercalary growth over the entire thallus is displaced outwards in an accumulating manner, accelerating the pustules. Moving away from the centre the pustules expand, often collapse in the middle, and mature by developing isidia. In the less active (senescent ?) margins the pustules are eroded away and the supplementary intercalary growth seems insufficient to keep the outflowing thallus intact. Thus the margins are disrupted into irregular lobes.

Type
Research Article
Copyright
Copyright © British Lichen Society 1997

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