Flora of New Zealand Series

Thallus fruticose, erect to pendulous or decumbent, radial, ± filamentous, simple to complexly branched, branches often attached to substrate by a holdfast, primary branches stout, tapering towards apices of secondary branches, ± terete or angled or partly flattened, smooth, or faveolate, waxy or shining, with or without spinules, pseudoisidia, papillae, fibrils, or soredia, yellowish, straw-coloured to pale greenish-blackened near holdfast in some species with or without red pigmentation. Medulla variable in thickness with a central chondroid axis of longitudinal hyphae, usually solid, tough, cartilaginous. Photobiont green, Trebouxia. Apothecia lecanorine, lateral or subterminal, disc rounded, plane or subconcave, surrounded by a thalline margin and furnished with ray-like branchlets, smooth, or minutely warted, often pruinose, exciple smooth and waxy to wrinkled-verrucose or papillate. Ascospores 8 per ascus, simple, colourless, ellipsoid.

Usnea is a genus of c. 600 species especially well-developed in tropical areas, included in the family Parmeliaceae. Zahlbruckner [ Denkschr. Akad. Wiss. Wien math.-naturwiss. Kl. 104: 116 (1941)] lists eight species from New Zealand four of which are valid, but his account gives too restricted a picture of New Zealand's Usnea flora. Nineteenth century accounts relied a good deal on European taxa to describe species collected from New Zealand and rather few local species were described. The most comprehensive of these [Stirton T.N.Z.I. 30: 387-392 (1898)] records 10 taxa from New Zealand of which U. xanthophana, U. acromelana (now included in Neuropogon), U. oncodes and U. torquescens are still valid. In the 1930s specimens collected by G. Simpson, J.S. Thomson and H.H. Allan were sent to J. Motyka in Poland, and in his monograph of Usnea [ Lich. Gen. Usnea Stud. Monogr. 1: 1-304 (1936); Ibid. 2: 305-651 (1937-38)] 23 species are recorded from New Zealand collections. Motyka's list however, contains several synonymous taxa and Martin's catalogues [ T.R.S.N.Z. (Bot.) 3: 153 (1966); T.R.S.N.Z. (Bot.) 3: 205 (1968)] record 45 species from New Zealand with many erroneous and synonymous taxa represented. The present account discusses 15 species which seems an appropriate representation for a mainly temperate region where one would not expect the rich speciation characteristic of tropical areas. Of this number, 6 species appear to be endemic to New Zealand. Recent studies of Swinscow and Krog [ Norw. J. Bot. 21: 165-185 (1974); Ibid. 25: 221-241 (1978); Lichenologist 11: 207-252 (1979)] on Usnea in East Africa discuss some species found also in New Zealand and these accounts are of considerable help in understanding this difficult and polymorphic genus.

Species of Usnea colonise a wide variety of habitats from alpine rocks, alpine and subalpine heaths (both on soil and on shrubs), forest trees from s.l., to treeline, introduced trees and shrubs (particularly fruit trees), fenceposts and power poles and wooden farm buildings. In forested areas, canopy branches often support a rich growth of Usnea (frequently U. capillacea and U. xanthophana, and in some areas specimens of Podocarpus hallii and Libocedrus bidwillii are so densely smothered in Usnea that photosynthesis in the host is inhibited and trees may even die. Interestingly, canopy species of Usnea are usually different from species of Usnea epiphytic on trunks of the same host tree. Usnea is still poorly understood in New Zealand, and in North I., especially, needs further collection and study. In disturbed habitats one or two wide-ranging species are successful colonisers of both native and introduced vegetation and also man- made substrates, especially decorticated wood (fenceposts, etc.), and changes in microhabitat and microclimate appear to induce a bewildering range of forms. Chemistry seems helpful in segregating species of Usnea occurring in New Zealand and should be used as a routine taxonomic tool.