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The Flora of New Zealand.
The Lichens.
W. Martin B.Sc.
Compiled by Ivor Hughes

Lichens.
Lichens are spore-bearing plants of lowly organization found in all altitudes and latitudes, where they grow attached to stones, dead logs, or bark, or else on the earth itself. Many kinds form the round, crustaceous patches seen on the surfaces of dry rocks, and have the reputation of being able to withstand drought and desiccation for a longer period than any other kind of plant�a period measurable in months or even years. Others have no very definite shape at all, but form scaly or powdery or granular patches on logs or bark. Still others form large leafy expansions attached to the tree or rock by a comparatively small base. Such are the foliose or frondose lichens, so exceedingly conspicuous and ornamental as at once to attract notice.

Now every lichen differs from most other plants in being a dual organism built up of a fungus and some species of microscopic alga living in the most intimate association and apparently with mutual advantage; for it is certain that many lichens can thrive in places and under conditions which neither partner could tolerate alone. The green or blue-green cells of the algae are able to manufacture carbohydrates like any other green plant, and these are shared with the fungus in return for water and mineral salts absorbed by it from the substratum or atmosphere. Each individual lichen resulting from the association of a specific alga with a specific fungus bears such a close resemblance to its fellows that we treat all such as though they were members of a common species, as with other plants.

The main body of a lichen, be it large or small, crustaceous, leafy, or shrubby, is termed the thallus; and the conspicuous discs or shields seen on the margins or surface of the majority are the spore-producing apothecia. In place of these, other lichens produce partially immersed "perithecia," or cavities opening by a tiny orifice, which serve the same purpose. The spores in all cases are those of the fungus only and they cannot reproduce the lichen unless they come into close association with the proper alga; but, fortunately, these lichen-forming algae are the most omnipresent of all forms of vegetation, being found in oceans, rivers, soil and air.

A further means of propagating lichens is by means of "soredia," small clusters of algal cells with associated fungal hyphae which burst through the outer skin of the lichen and form a dusty powder on the surface of the thallus. Several botanists of world-wide repute have commented on the great wealth of lichens that inhabit New Zealand, and on the inclusion amongst these of some of the largest, handsomest, and most interesting of all known species. A large number are cosmopolitan, being found in suitable localities throughout the world; others have a very wide distribution in southern lands only; while many more are apparently restricted to the New Zealand area.

Amongst the hundreds of species, there will be found great variation in form, colour, and structure. Many crustaceous lichens colour or discolour the bark of trees, the surface of the rocks, clay banks, and similar surfaces. Others have erect or pendulous, branching stems and are termed fruticose, but most conspicuous of all are the scores of foliaceous lichens that we see adorning the trunks of forest trees, or adhering to exposed rock-faces.

Now, though lichens may range very widely over the earth, most species show a preference for particular localities, stations, or substrata. Some attach themselves only to the harder rocks, some to the softer; many grow only on bark, or on wood, or even on leaves; others take up their abode on dead mosses, and a few are actually parasitic on other lichens. Not a few are less fastidious and live on rocks or on trees quite indifferently.

Again, there are a number of lichens (e.g., Lichina pygmaea, Verrucaria spp., etc.) found on rocks even below high tide mark, and others restricted to sub-alpine or to alpine stations. Some species live only near water or in damp stations, and others clothe sun baked rocks. Several genera (e.g., Cladonia, Stereocaulon, Nephroma) have their maximum development in high latitudes or altitudes, while a few are essentially tropical (e.g., Sticta, Pseudocyfhellaria).

Thus New Zealand lichens comprise all types � tropical, temperate, and arctic; coastal and montane; corticolous and saxicolous; cosmopolitan and endemic; the largest and the smallest known. Many lichens can thrive under extremes of climatic conditions such as other plants could not tolerate, and, as a consequence, they form the last visible outposts of the plant world as we travel towards polar lands, scale the mountain peaks, descend to the sea, or invade the torrid tropical desert. Many, even in New Zealand, can remain dry as dust, and brittle as glass for months on end, and still flourish and grow on the return of more congenial conditions.

Not a few New Zealand lichens could, if required, be used as a source of dye-stuffs. The modern lichenologist not only takes notice of the form of the lichen but also of the component fungi and algae, when drawing up his scheme of classification; but to the non-technical observer, it will still be found convenient to adopt the older scheme. and group lichens as:

The gelatinous character of many lichens results from the presence in most of the well-known, blue-green, mucilaginous alga known by the name Nostoc. Many of these have a small, dark, lobed, leafy thallus bearing small reddish or brownish apothecia and belong either to the genus Collema, to the allied genus Leptogium, or to the foliose Dog-lichen (Peltigera), all of which are restricted to very damp stations on rock or in forest. The dark brown, coastal Lichina already referred to belongs to this group, its shrubby stems rarely half an inch high being found on occasion associated with the mossy seaweed known as Bostrychia, which is submerged for several hours every day. Here, however, Rivularia replaces Nostoc as the alga.

(1) Crustaceous Lichens: The species of this group outnumber all others combined. It is scarcely possible for the ordinary observer to identify the numerous species except in the case of those possessing very distinctive attributes. The largest genera in New Zealand are Lecidea, Verrucaria, and Lecanora, with close on 200 species between them. On damp clay banks, a very common and abundant plant is the Rose Lichen (Baeomyces roseus), or one of half a dozen closely allied species, easily recognized by the pink-topped, white stalks which arise at intervals from the whitish thallus. No other New Zealand lichen has spore-bearing "podetia" quite like those of Baeomyces. Various lichens of this class being amongst the first plants able to live on freshly-exposed rock surfaces, serve to initiate the evolution of a fertile soil capable of supporting the "higher" plants. If one carefully observes any exposed bank, cliff, rock, wall, post, tree-trunk, or like surface, one will rarely fail to find these diminutive plants carrying on their important but unobtrusive work. The genus Graphis and a number of allied genera have the apothecia in the form of linear, black lines either simple, curved, or branching, and to this feature they owe their generic name. The thallus is rarely visible but the apothecia, though tiny, are quite conspicuous on the bark or rock where they happen to have developed. At least two species grow abundantly under overhanging ledges on coastal rocks. Species of Wartwort (Verrucaria) are commonly recognized by the areolate surface, each areole containing sunken, spore-producing perithecia opening by an elevated pore at the surface. Almost if not all grow on rocks, and many partially gelatinous species grow near streams or in maritime stations. The whitish and greenish-white colour of coastal rocks is commonly attributable to species of Wartwort, in conjunction with species of Caloplaca, Buellia, Lecanora, Paxmelia, Pertusaria, and other Crustaceous lichens.

(2) Foliose Lichens: Lichens of this class are much the most conspicuous in our lichen flora, most of them being of large size and leafy habit. The largest of all belong to a family called the Stictaceae (or Stictae), of which an eminent Scottish botanist (Dr. Lauder Lindsay) once wrote: "New Zealand is par excellence the country of the Stictae. Not only do they occur in the greatest absolute as well as relative numbers, but there they attain their maximum development, size, and beauty. This preponderance of the Stictae, their frequent size, and beauty of colouring, and the profusion of individuals, give a somewhat peculiar character to the foliaceous lichen flora of New Zealand"; but, with equal truth, he also remarks that "The Stictae are one of the most variable and puzzling groups of the higher or foliaceous lichens. As in other families and genera extreme forms are sufficiently distinct. Gradation forms exist between all, so that it defies one's power to delimit a species at all."

Most of our three dozen or more species were at one time placed in the genus Sticta, which, however, later students have subdivided into six sub-genera, three of which (Sticta, Pseudocyfhellaria, and Lobaria) usually contain green gonidia � a name applied to the algal cells�and three (Stictina, Cyanosticta, and Lobarina) blue-green algae. Excepting the last-named genus in each of the above groups, these lichens bear on their lower surfaces characteristic aerating white or yellow pits, which, if empty, are termed cyphellae, but pseudo-cyphellae when filled with fungal hyphae. The name Sticta formerly applied to all, and usually applied still to the cyphellate species, bears allusion to this pitted lower surface which distinguishes these lichens from all others.

It is difficult to select from these large foliaceous lichens forms more worthy of mention than others, for many are abundant and widely distributed over New Zealand. The Elephant's Ear {Sticta latifrons) has such a tiny area attached to the tree-trunk as easily to be distinguished. The thallus is large, glaucous above and brown below, and bears scattered brown apothecia on the central portions. Perhaps the most beautiful forest lichen is the Golden Sticta (Sticta aurata), a brownish or copper-coloured lichen margined with gold powder (soredia), internally yellow as ochre, and dotted on the dark brown lower side with numerous golden pits. The Tawny Moss Lichen (Sticta crocata), dark reddish - brown or greenish-brown on both surfaces, has rows of orange-yellow soredia on the margins and reticulations of the top surface, and yellow pits below, but internally the lichen is white. This species, though found occasionally on tree trunks, is more common on moss-covered rocks or clay banks, especially in maritime stations.

Other common foliose lichens growing mainly on moss are S. fragillima and Peltigera dolichorrhiza. Sticta fossulata and S. orygmaea, with black apothecia, and S. jreycinetii, with red apothecia, are other abundant representatives. Lobaria adscripta is the commonest non-cyphellate representative member of the group.

Another family of foliaceous lichens even more numerous in species but showing a much greater range in size and including several of extreme abundance and considerable proportions, is that of which Parmelia is the characteristic genus. The majority of species are white, grey, slaty-blue, or yellowish-green lichens bearing rather large brown apothecia and attached to the rock or bark by means of black root-like fibrils. Not a few have the upper surface covered with powdery warts or soredia.

Several of the commonest species reach their maximum development on coastal rocks. Such saxicolous species include the Grey Crottles (P. saxatilis and P. prolixa) and the Green Crottle (P. conspersa). Other common rock-encrusting Parmelias, are P. laevigata, P. olivacea, and P. perforata, and these might appropriately be termed the Warted Crottle, the Brown Crottle, and the Perforate Crottle.

The name Crottle was that applied by Scottish peasants to those lichens from which they obtained the dyes used for colouring cloth and wool before the advent of coal-tar and other synthetic pigments. Commonest of such crottles was Lecanora tartarea, better known as Cudbear. This is also a New Zealand lichen. Of the bark-encrusting Parmelias, the commonest include local forms of P. perforata (so named because the apothecia are often perforated in the centre), P. pertusa, and P. subphysodes, a glaucous-grey species with sorediate lobes.

The Blue-edged Nephroma (Nephromium lyallii) is a beautiful forest lichen with a livid green or brown thallus edged with blue. All the lichens of this genus have the apothecia on the under surface of the thallus but are exposed by the turning upwards of the fertile lobes. A- more common species is N. zelandicum. None of them invade the tropics or even sub tropical areas, being essentially plants of mossy tree-trunks in cool-temperate, or sub-Antarctic and arctic regions. Between the typical foliose' lichens and the truly crustaceous forms there are many of intermediate habit. Amongst these are a number of orange or yellow species specially abundant on rocks near the sea. The Golden Crottle (Xanthoria parietina) is not only the commonest of these in New Zealand, but a lichen of world-wide distribution, while several of the others are amongst the most arctic, Antarctic, and alpine lichens in the world. Foremost among such are two species of Placodium which approach the Poles more nearly than almost any other plant, as well as being found at altitudes up to 22,000 feet on the Himalaya Mountains, where they colour the rocks bright orange-red. Telo-schistes flavicans is a small lemon-yellow sub-fruticose lichen of tufted, filamentous habit equally common both at high altitudes and at high latitudes, and not infrequently associated with Placodium. Much more common in New Zealand, however, is a second species of this genus (T. chrysophthalmus) which often smothers the stems of shrubs growing near the sea with small, strap-shaped, bright yellow or orange, subfoliose individuals abundantly provided with terminal orange-red apothecia.

(3) The Fruticose Lichens: In this group are placed all lichens of erect or pendulous shrubby habit. Most of them thrive best on barren soils in a humid atmosphere, and the group reaches its maximum development in the fells of Siberia, Norway, and Iceland in the north, and of Kerguelen in the south, where they form a thick, ashy-grey carpet known as lichen-heath. Its most abundant representative is a lichen commonly called Reindeer Moss from the fact of its providing the reindeer with almost its sole winter food.

On paling fences, neglected fruit trees, dead branches of sub-alpine forest trees, exposed rock faces, and even on alpine rocks, one may find without difficulty one or more forms or species of Usnea, better known as the Aaron's Beard Lichen. Commonly these form greenish-grey or yellowish-green, erect or pendulous tufts of branching fibres, varying from one to twelve inches in length, and occasionally bearing large, flat, fringed discs or apothecia on the ends of some of the branchlets. A black and yellow species (Neuropogon melaxantha) is much the most abundant alpine lichen on many high alpine rocks of New Zealand mountains.

In number of species (46) the genus Cladonia holds pride of place. Its very numerous members are nearly all to be found growing on clay banks, peaty soils, manuka heaths, or sub-alpine moorland. At first the thallus is crustaceous or scaly, but later it takes the form of a simple or branched, erect podetium or stem, which may either taper to a point or expand into a conical cup. The podetium itself may be scaly or smooth, grey-green or white or ash coloured, one to three inches high, and terminate either in brown or in scarlet apothecia. Most conspicuous and beautiful of all is the alpine Coral Lichen (C. retipora) with densely tufted podetia forming a reticulated network of brittle substance when dry, and delicate lace-like form. Not greatly dissimilar are C. aggregata and C. sullivani, also with perforate podetia. More common is the greenish Cup-moss or Pyxie Cup (C. pyxidata) and the somewhat similar Slender Pyxie Cup (C. gracilis) to be seen on clay banks in all parts of the country; and even more conspicuous are the scarlet-topped Horn of Plenty lichens (C. pleurota, C. defdrmis, etc.), trumpet-shaped lichens resembling the pyxie-cup, frequently bearing on their upper margin a number of smaller trumpets besides the scarlet apothecia. On rocky banks C. capitel-lata, with erect, white, branching stems, and, on bogs and damp sub alpine stations as well, C'. pycnodada are also very abundant representatives.

Associated with these Cladonias, one commonly meets one or other species of Stereocaulon or Sphaerophorus. Stereocaulon ramulosum is at once the commonest and the largest representative of the first-named genus. Its podetia range up to five or six inches' in height and are copiously branched. Occasionally one may observe pale violet, globular "cephalodia" on the branches. Of the four species of Sphaerophorus which, though possessing a totally distinct alga from the Stereocaulons, greatly resemble them, S. globosus with round branches and S. melanocarpus with flattened branches are native to Britain as well as to New Zealand. These are found mainly on tree-trunks and on old logs. A very common genus of fruticose lichens known as Ramalina is represented in New Zealand by eight or nine grey-green species tufted like the Aaron's Beard, but with flattened, often perforate, stems bearing disc-shaped apothecia on the margins or upper surface. These are common on exposed rocks, particularly near the sea and on the stems of isolated shrubs, which they clothe in a mantle of grey. Finally, on bogs and heaths, the hollow worm-like, chalky-white prostrate stems of that widespread lichen known as Thamnolia may commonly be found, especially in mountain regions.

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