Umbilicate growth form

The thallus of foliose lichens is formed by flattened lobes, which are heteromerous and dorsoventral in structure. Two principal types, the laci-niate and the umbilicate growth form, can be distinguished. Laciniate thalli adhere more or less firmly to the support on which they grow. Either the whole lower surface is in contact with the substrate or the margin of the lobes becomes free and bends upwards. The thalli are usually attached by rhizines or rhizoidal hyphae. The umbilicate lichens are platelike and attached by a central discoid holdfast called the umbilicus (Fig. 47). 

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