General Morphology and Ecology

Cladonia as a genus is characterized by the presence of a dorsiventral primary thallus either crustose, foliose, or much more commonly squamulose in character, from the margin or surface of which one or more simple or branched, hollow podetia arise, variously terminated by saucer-shaped or goblet-shaped expansions known as scyphi, by apothecia, by spermagonia, or frequently by subulate, furcate or blunt, sterile apices. These podetia may exceed 15 cm in height, but more commonly are less than half of this.

The apothecia are turgid reproductive structures of variable size containing asci, each with eight fungal ascospores. The spermagonia or pycnidia are smaller, cylindrical or fusiform bodies containing what are believed to be non-motile male cells variously termed pycnidiospores, spermatia, or conidia, surrounded by a clear or reddish jelly-like matrix. Their true function is still not certainly known, but in any case reproduction in Cladonia is mainly vegetative, every part of the lichen being capable of initiating new individuals. Mealy or granular soredia and coralloid isidia are special structures containing both fungal hyphae and unicellular algae or gonidia, developed to ensure reproduction and distribution.

The podetial wall typically comprises three distinct layers—an outer cortex, an inner chondroid or cartilaginous layer, and an intermediate medullary layer—but any one or two of these may be absent from the whole or part of the podetium in a number of species. The cortex may be continuous or almost so; or it may be broken up into patches, into areolae, or into verruculae. The outer surface may be smooth, rugose, tomentose, squamulose, sorediose, or isidiose.

From the simple, cylindrical type of podetium an evolutionary advance leads to its upward expansion into a shallow or deep scyphus, or to a variously branched structure reaching its highest development in the Cladinae. Here the branching may be sympodial, dichotomous, or polytomous. The scyphi may be sterile, or may be margined with apothecia, spermagonia, or proliferations of various forms.

In the more primitive species, the primary thallus is generally well developed, large, and persistent, whereas the podetia are simple and short. On the other hand, the more advanced species have usually a small and often evanescent primary thallus, while the podetia are commonly tall and robust, scyphose, or much branched. The spermagonia and occasionally the apothecia in the more primitive members are usually borne on the primary squamules; but the more advanced species bear both apothecia and spermagonia on the podetia.

Most Cladoniae are highly xerophytic and grow on barren or acid soils, in heaths, or on peat, rotting logs, or decaying tussock bases. Some are frequent on roadside banks or on a thin soil veneer overlying rock. Though they occur commonly in areas both of high and of low rainfall, in general they avoid permanently saturated substrata. They are harmed neither by drought nor by frost. Most species are photophilous and none can grow in deep shade, nor do they thrive in a smoky atmosphere. Some species are mainly montane or subalpine; others are confined to the lowlands.

The greatest concentration of species or of individuals in New Zealand occurs in manuka heaths, on decaying logs on the forest margin, or on the dead bases of Danthonia tussocks margining areas of peat. As many as a score of species or even more may occur in an area twenty metres square. Podetial squamules are most strongly developed in damp areas screened from direct sunlight.