The slow RGR of many crustose species combined with the difficulties of growing such lichens under controlled conditions for long periods in growth cabinets has made it especially difficult to study their growth. Hence, relatively little is known about the nature and processes of growth, the range of growth rates shown by most species, on the relationship between growth and thallus size (the growth rate-size curve), or on the influence of environmental factors on growth. This lack of fundamental knowledge is of particular concern given their widespread use in lichenometry – a widely practiced surfacedating technique.