Lichens are small unusual plants found on rocks, soils, tree trunks, on leaves, fences, and paths. They are of slow growth, are long lived, and are found all over the world, from polar regions to the equator, and from sea level to mountain tops. They are able to withstand extremes of temperature and long periods of drought. These small plants do not have roots, stems, or leaves but appear as spreading crusts, leaf-like mats, or hanging threads, mainly grey or yellow-orange in colour.
A lichen is a composite plant consisting of two organisms living together for mutual benefit. A particular species of fungus lives in symbiotic association with a particular species of alga to form a distinct plant body. When a cross section of a lichen is examined under a microscope, a layer of green or blue-green algae is seen beneath the tangled formation of colourless fungal hyphae. The fungus forms the protective layers which shelter the alga while it carries on photosynthesis and makes food for both partners.
Reproduction may be from fragments of the plant body containing both the fungus and the alga, as in Sticta and Parmelia. Spore capsules, either apothecia or perithecia, are formed by most fungi, and from these are ejected fungal spores which, however, must combine with the particular alga to form a new plant. In some species, such as Cladonia, algal cells become surrounded by fungal hyphae and form powdery masses (soredia) on the surface of the plant. These are distributed by wind and rain.
Many lichens are cosmopolitan and may not be restricted to any particular substratum or habitat. Many are endemic to New Zealand; there are over 1,250 species belonging to 150 genera already known, and it is probable there are many more to be identified.
Lichens may be classified, according to their form, into three main groups as foliose, fruticose, and crustose, with many intermediate forms.
There are about 50 genera of foliose lichens in New Zealand. Their appearance is that of a flat continuous thallus, attached to the substratum by some form of holdfast. The genus Sticta and the genus Parmelia are the largest, both in number of species and in size of plant body. There are over 50 species in each of these genera. Stictae are found mainly in the Southern Hemisphere. Among the larger species are S. coronata, S. flavicens, S. impressa, S. fovelata, and S. polychrita, all distinguished by pits on the lower surface.
Parmelias, somewhat similar in appearance, are black on the under surface. The genus Piltigera, found on damp earth, is represented in New Zealand by nine species. Like the four species of Nephroma, found on rocks and tree trunks, most of these are dark green on the upper surface and white below. Umbilicaria, eight species, are black and very small. Collema and Leptogium become gelatinous when damp. The large yellow-orange Xanthoria is found on trees and rocks near the sea.
These lichens have a branching thallus, some with bushy or erect appearance. There are 27 indigenous genera of which the largest is Cladonia, with 70 species. Cl. chlorphoea and Cl. pyxidata have erect podetia bearing brown apothecia, while on Cl. coccifera and Cl. deformis the apothecia are scarlet. There are three species of Cladia, the coral lichen, with masses of white or grey branches. The commonest is C. aggregata, found in all parts of this country.
Stereocaulon has nine indigenous species, both large and small, the most common being S. ramulosum and S. corticulatum, which frequently cover roadside banks. There are over 20 indigenous species of Usnea, some of which are bushy and erect while others are thread-like and pendulous, mainly grey-green or yellow in colour. The four species of Neuropogon found here are distinguished by black tips to the yellow or grey branching portions. The genus Sphaerophorus is represented here by five species, two with a flattened green thallus, while S. tener is a bushy lichen on forest trees, with black apothecia.
These form a thin crust on a substratum from which it is almost impossible to detach them. There are representatives of over 70 genera in New Zealand. The genus Lecidia has many species, also the genera Bacidia Arthonia, Buellia, Lecanora, Verrucaria, Rhizocarpon, and Lopadium are well represented here. Many indigenous species of Pyrenula are found on the trunks of forest trees.
Some New Zealand lichens have useful chemical and dyeing properties. Sticta coronata, which is found mainly on forest trees and shrubs and sometimes measures more than a foot across – green with purplish patches, and yellow underneath – has yielded polyporic acid, which shows promising effects on leukaemia in mice. Dyes of a wide range of colours can be made from species of Sticta. Usnea, or “Old Man's Beard”, found hanging from old trees and fences, produces dyes in shades of brown and orange.
New Zealand lichens were first collected by botanists on Captain Cook's visits. The Forsters gathered specimens on Cook's second voyage in 1772, and Menzies collected lichens during Cook's third visit.
The first collection of any size was made by Dumont d'Urville and others during the voyage of the Astrolabe, 1826–29, and 26 specimens were described by A. Richard in his Essai d'une Flora de Nouvelle-Zélande, published in 1832. Drs Lyall and Hooker added greatly to the knowledge of New Zealand lichens with specimens collected during the voyage of the Erebus and Terror in 1840–41. Thirty-one species from the Auckland and Campbell Islands were named by Thomas Taylor and J. D. Hooker in Hooker's Botany of an Antarctic Voyage, of 1844.
The next major contribution was made by W. Colenso, whose specimens were described by the Rev. Churchill Babington, in Hooker's Flora Novae-Zelandiae of 1855. Dr W. Lauder Lindsay collected lichens in Otago in 1861 and in a paper read in 1886 mentioned about 100 species. By 1867 just over 200 species appeared in Hooker's Handbook of the New Zealand Flora.
Zahlbruckner's Lichenes Novae Zelandiae, published in 1941, is the most important publication of this century. Using the collections of H. H. Allan, L. M. Cranwell, L. B. Moore, J. Scott Thomson, J. E. Holloway, and K. W. Alison, Zahlbruckner described about 600 species. Papers by William Martin and J. Murray appeared in the Transactions of the Royal Society of New Zealand in 1958 and 1960.
Much remains to be done both in collecting and in identifying New Zealand lichens. Microscopic examination is usually necessary for the identification of species. As few type specimens are available in New Zealand, reference must be made to the collections at Kew, the British Museum of Natural History, and the Natural History Museum of Paris. Jeanne Hannington Goulding, Botanist's Assistant, Auckland Museum and William Martin, B.SC., Lichologist and School Teacher (retired), Dunedin.
by Jeanne Hannington Goulding, Botanist's Assistant, Auckland Museum, and William Martin, B.SC., Lichenologist and School Teacher (retired), Dunedin.