Flora of New Zealand Series

Thallus homoiomerous, lobate, subcrustose, foliose to ± fruticose, subgelatinous, ± transparent, opaque, pliable when wet, except for a few species not noticeably swelling when wet, wrinkled, papery when dry, corticolous or saxicolous. Lobes flattened, orbicular to elongate, to crowded-congested and ± subascendent, margins entire or lacerate-crenulate or isidiate, upper surface smooth, undulate or wrinkled-plicate or lobulate or isidiate, soredia absent, lead-grey to bluish or greenish or livid brownish at margins, rarely completely red-brown or brown. Cortex of a single layer of irregularly isodiametric cells on both upper and lower surfaces. Photobiont blue-green, Nostoc, randomly distributed as scattered chains throughout thallus. Lower surface smooth or wrinkled, glabrous or tomentose. Apothecia emergent, adnate, sessile or shortly pedicellate, laminal or occasionally marginal, disc pink to red-brown or black, epruinose, both thalline and proper exciples normally present, thalline exciple sometimes lobulate. Ascospores (4-)8 per ascus, fusiform-ellipsoid to oblong-fusiform, ± submuriform with 2-11 transverse septa and 1-2(-10) longitudinal septa, apices rounded or pointed.

Leptogium is best developed and reaches its greatest abundance in tropical regions, however it is widely distributed with some species reaching arctic and antarctic regions. It is distinguished from Collema by the presence of a true cortex of a single layer of irregularly isodiametric cells on both upper and lower surfaces, but the precise limits between the two genera are not clearly defined in all cases. About 150 species are described. Wilson [ J. Linn. Soc. Lond. Bot. 28: 353-374 (1891)] described seven species from Australia, at least two of which occur also in New Zealand. North American species are monographed by Sierk [ Bryologist 67: 245-317 (1964)] an account which contains much useful information on the genus. Malme [ Ark. Bot. 19 (8): 1-29 (1924)] discusses South American taxa, and Awasthi and Akhtar [ Geophytology 8: 189-204 (1979)] species from India. Jørgensen [ Sv. Bot. Tidskr. 67: 53-58 (1971); Herzogia 2: 453-463 (1975); Herzogia 3: 433-460] deals with species in section Mallotium (tomentose on the lower surface) at least three of which occur in New Zealand.

Leptogium in New Zealand is still very poorly known and much in need of collection and revision. New taxa from New Zealand were proposed by Nylander [ Lich N.Z.: 10 (1888)], Müller Argoviensis [ Bull. Herb. Boissier 2, App. 1: 17-18 (1894)] and Zahlbruckner [ Denkschr. Akad. Wiss. Wien math.-naturwiss Kl. 104: 269-271 (1941)].

Nine species of Leptogium are recorded in Zahlbruckner ( loc. cit. ) and in Martin and Child ["Lichens of New Zealand" pp. 73-74 (1972)], while Martin [ T.R.S.N.Z. (Bot.) 3: 139-159 (1966); T.R.S.N.Z. (Bot.) 3: 203-208 (1968)] catalogues 20 taxa. None of these accounts are based on a close study of New Zealand collections or on examination of relevant types, and many Northern Hemisphere taxa are mentioned when mainly Southern Hemisphere species appear to be involved.

Species of Leptogium have ecological requirements similar to those of Collema preferring damp, shaded habitats and high humidity. The genus is divided into five sections (Sierk loc. cit. ) representatives of three of which are found in New Zealand. In this account 9 species are recognised.