Distichophyllum Dozy & Molk.

Plants small to robust, soft, iridescent or not, usually complanate, mostly terrestrial and often forming layered mats. Stems erect or prostrate, sparsely branched, in cross-section lacking a hyalodermis, lacking distinct cortical layers, and lacking a central strand, sparsely beset below with brown to red-brown, ± smooth rhizoids. Shoots mostly complanate, but sometimes nearly terete. Leaves in 6–8 ranks, widely or closely spaced, mostly symmetric, oval, elliptic, or obovate, apiculate or rounded at apices, mostly plane, entire, bordered or occasionally unbordered (as in D. microcarpum), those of ventral and dorsal ranks smaller than those of lateral ranks; upper laminal cells smooth, firm-walled, ± hexagonal, compact, becoming larger and laxer towards the base, occasionally inflated and pale adjacent to the lower costa; alar cells not differentiated. Costa single, narrow, often forked in upper portions, usually ending well below the leaf apex.

Autoicous, dioicous, or rarely synoicous. Perichaetial leaves with weak border and costa ± absent. Perigonia lateral on stems, gemmiform, bracts with weak border and costa ± absent. Setae lateral or ventral (as in D. microcarpum), erect, smooth or papillose, mostly red-brown; capsules horizontal, pendent, or occasionally nearly erect, symmetric, oblong-cylindric from a tapered neck, smooth or tuberculate; exothecial cells collenchymatous, rarely (in D. microcarpum) with arching secondary thickenings converging over the lumen; annulus narrow and falling with the operculum or absent; operculum long-rostrate from a conic base. Peristome double; exostome teeth yellow to brown-yellow, linear-lanceolate, furrowed, densely and finely cross-striate, with high lamellae on inner surface that project laterally to form marginal trabeculae; endostome pale yellow, finely papillose, with a moderate to high basal membrane; endostome segments usually well-developed and usually ± perforate; cilia rudimentary or absent. Calyptra mitrate-rostrate, often hairy, fimbriate at base. Spores small.

A large genus with up to 100 species, distributed mostly in Malesia and Oceania, but with a secondary centre in the cool-temperate regions of the southern hemisphere. Many of the described species are recorded from a single island or land mass. The palaeotropical species are often difficult to distinguish with confidence and the genus needs a large-scale taxonomic revision; it is likely that this would result in drastic reduction of the number of recognised species. Four species occur in N.Z., one with two varieties. The N.Z. species are somewhat anomalous in the genus in that all are dioicous with the exception of the autoicous D. crispulum var. adnatum. In the intra-generic classification of Brotherus (1925, p. 227) all but one of the N.Z. species (D. microcarpum) are placed in the section Discophyllum. While a firm case could be mounted on morphological grounds (discussed under that species) for the segregation of D. microcarpum, this is not advocated here.

Streimann (1999) presented a revision of seven species occurring in Australia that is useful in N.Z. Matteri's (1975) earlier monograph of Andean/Patagonian Hookeriaceae also included useful information on this genus, but her species concepts are narrower than those applied here and there is only modest species overlap with N.Z.

The genus Distichophyllum was based by Dozy & Molkenboer (1845–1854) on three species, of which two (D. cuspidatum and D. spathulatum, both from Java) were retained in the genus by Brotherus (1925). One of these two species should be selected as the generitype.

In the following key and descriptions, the phrase "upper laminal cells" refers to cells midway between the termination of the costa and the leaf margin.

Distichophyllum aloma Müll.Hal. (1902) was tentatively placed in synonymy in 1907 with D. microcarpum by Brotherus (1901–1909, p. 930). The type specimen (T. Kirk 502 from "Ligars Gulley", Auckland) has not been seen, but is likely in the Stephani herbarium at Geneva.

Hookeria amoena Colenso (1886) and H. smaragdina Colenso (1886) are discussed briefly under D. rotundifolium.

Hookeria cataractae Colenso (1887) and H. concinna Colenso nom. illeg. (1886) were both placed by Dixon (1927, p. 282) as synonyms of what is termed here D. crispulum var. adnatum. Colenso’s type locality (near Norsewood, Wellington L.D.) for both these names is far south of the known distribution of the var. adnatum. Therefore Dixon’s synonymies are questionable. However, in the absence of type material, these names are not further discussed here.

Hookeria flexuosa Mitt. in Hooker (1867) and H. subsinuata Colenso (1886) were both tentatively placed by Dixon (1927, p. 282) in synonymy with the taxon treated here as D. crispulum var. crispulum. It is unlikely that Dixon saw type material for these names and their type localities are far south of the confirmed distribution of the var. crispulum. Therefore Dixon’s synonymies are questionable, and these names are not further discussed here.

Hookeria microclada Colenso (1886) and Distichophyllum zuernii Schlieph. in Müll.Hal. (1902) are both discussed briefly under Distichophyllum pulchellum.