Introduction

The subsection Cladina of the genus Cladonia has a world-wide distribution, but together with the genus Stereocaulon it constitutes the dominant vegetation of much of the Arctic tundras where three species are together known as “Reindeer Moss”. Till recently the Cladinae were deemed to be a subgenus of Cladonia, but in a recent revision of the genus, Mattick (8) placed the Cladinae as a subsection of the section Perviae in the subgenus Eucladonia. The species comprising the subsection are characterized by a crustose primary thallus giving rise to intricately branched, interlocking podetia forming compact or open cushions sometimes of considerable extent.

The surface of the podetium is rarely corticate, being more commonly arachnoidtomentose (cobwebby), with or without superficial areolae or verruculae. The colour is variously white, cream, yellow, yellowish-green, ashy, grey, or grey-green, and the ramification is variously dichotomous, trichotomous, or polytomous, or a combination of these. When one branch of a dichotomy or whorl develops more strongly than the other or others a sympodial axis may result. In some species (e.g., C. alpestris) such a sympodium may extend from base to apex, while in others (e.g., C. impexa) it may be evident only in the lower half of the podetium. Sometimes a single branch may occur between two whorls, unilaterally in C. sylvatica, divergent in C. mitis.

Apothecia and spermagonia are small or even minute, both being situated on the apices of the terminal branchlets. The spermagonial contents are embedded in either a clear or reddish jelly, the colour being constant in each species but rarely available at a suitable stage for diagnostic purposes.

Species discrimination is rarely easy. Many species are superficially much alike, and only careful examination of the ramification, the nature of the ultimate branchlets, of the colour, of the axils, and often of the lichen substances present in the podetia, can reveal the true identity of a specimen. The ultimate branchlets may be short or long, curved or straight, stout or slender, spreading or deflexed, and then unilaterally or divergent.

Santesson (11) has observed that in the Cladinae the lichen acids are fairly constant for each species, and therefore are of great value in the discrimination of single specimens; but both he and Mackenzie Lamb emphasize that in their view, “the morphology and anatomy of the plant is fundamental in species discrimination,

and the presence or absence of a lichen acid in morphologically identical specimens of a normally acid-bearing species cannot be regarded as an important taxonomic difference”. With this contention the writer is in fullest agreement Fortunately in the Cladinae morphological distinctions do separate most of the species at present recognized, and total reliance on chemical differences is rarely necessary save in the case of atypical specimens.

In his monograph of the Cladinae (2) in 1939 as modified by later amendments, Des Abbayes has grouped the various species in five categories or series termed Rangiferinae, Alpestrae, Impexae, Bicornutae, and Tenues. These groups are fairly well defined and are of much service in classification, but the observation made by Bruce Fink, in 1903, still holds good that, “Nothing but the most careful observation will enable one to determine Cladoniae with any certainty, even with the best descriptions,” and this is specially true of the Cladinae where so many species are superficially very much alike.