Dicranoloma (Renauld) Renauld

Plants mostly robust, variable in colour when fresh, becoming gold-brown when dry, forming cushions or turves. Stems erect or occasionally trailing, branching by subperichaetial innovation and also usually by forking, in cross-section with an ill-defined central strand, matted with tangled, smooth, pale-brown or whitish rhizoids. Leaves falcate-secund or wide-spreading and ± straight, smooth or variably plicate or rugose, ovate-lanceolate, ovate, or linear-lanceolate, usually acuminate, obtuse or rounded apically, with a well-defined border (limbidium) of linear cells at least in the lower portion, spinose-serrate, serrate, or entire, clasping or not at insertion, strongly concave or subtubulose, plane at margins; mid laminal cells elongate or short, thick-walled, porose or not, a group adjacent to costa rarely differentiated and shorter; alar cells abruptly differentiated, inflated but firm-walled, unistratose. Costa narrow or robust, mostly well-defined for its entire length, usually percurrent or short-excurrent, occasionally fading in leaf base, variable in cross-section.

Dioicous (nearly always pseudautoicous). Perichaetia terminal, becoming lateral by innovation, the leaves sheathing and strongly concave, obovate or elliptic, often aristate. Dwarf males gemmiform, embedded in rhizoids of sterile or ♀ plants. Setae aggregated or single, elongate and straight, not twisted; capsules exserted or emergent, curved, cylindric, constricted below the mouth (when dry), strumose or not, smooth with moist, sulcate or smooth when dry; exothecial cells firm-walled, oblong-hexagonal or ± irregular; stomata restricted to neck, superficial; annulus weakly differentiated, not revoluble; operculum curved-rostrate from a conic base, ± equal to the capsule. Peristome teeth inserted at mouth, red-brown, divided c. halfway to base into segments of unequal width, papillose-striolate below, mostly baculate near apex. Calyptra cucullate, smooth. Spores spherical, nearly smooth.

Klazenga (2003) has provided an invaluable revision of Dicranoloma for Australasia, which followed an earlier (1999) revision of the Malesian species. Klazenga (2003) estimated that this predominantly southern hemisphere genus contained 35–40 species, with greatest species diversity in Malesia, followed by Australia, N.Z., and islands of the south-western Pacific. His key to species is useful for the identification of N.Z. material. He recorded 10 species from N.Z., compared to only 8 species accepted here. Dicranoloma trichopodum (Mitt.) Broth. is treated here in Holomitrium (following Klazenga 2006), and D. eucamptodontoides (Broth & Geh.) Paris is here excluded from the N.Z. flora for reasons detailed under D. obesifolium.

Klazenga’s circumscription of Dicranoloma is adapted here. An alternative view, placing the New Guinean species of Dicranoloma into Dicranum, was adopted by Norris & Koponen (1990). A broad circumscription of Dicranum was also followed by Fife (1995), but Klazenga’s subsequent publications have led to an alteration of this view. Features that distinguish Dicranoloma from the one species of Dicranum accepted in the N.Z. flora are discussed under the latter genus. A number of synonyms of Dicranoloma species have been accepted in this treatment without further investigation, many of them on the basis of Klazenga’s (1999, 2003) regional revisions.

Considerable emphasis has traditionally been placed (since Renauld 1909) on the systematic value of the structure of the costa viewed in cross-section. Renauld described four characteristic types: toxoneuron, leptoneuron, heteroneuron, and cyrtoneuron. Dixon (1913, p. 8–9, pl. IV) both defined and illustrated Renauld’s costal types and commented that "the different types of nerves described by Renauld, while of much value in the determination of species, and of no slight taxonomic importance, must not be looked upon as representing clearly defined and distinct groups of species, but rather as marked points in an intergrading series of types of structure." Sainsbury (1955, p. 126) expressed even greater caution about the use of the costal types to define species and noted that three of the types (excepting cyrtoneuron) "grade into each other".

In the present study, costal structure has been found to be of limited utility in delimiting species boundaries (with the exception of D. dicarpum, the only N.Z. species with a well-defined cyrtoneuron costal structure). An approach similar to that of Klazenga (1999) has been adopted: the costal structure for each species has been described in preference to assignment to a particular costal type.

The colour, degree of lustre, and general appearance of fresh plants are very useful features for the recognition of N.Z. species, but these features are often lost upon specimen drying. The number of setae per perichaetium and the relative length of setae to the perichaetial leaves are very useful for the recognition of some species, but sterile populations or specimens are frequently encountered. The form of the inner perichaetial leaves facilitates species definition and recognition in some instances. In D. fasciatum the ♀ leaves are narrowly lanceolate and gradually acuminate, rather than aristate or mucronate in all other N.Z. species. Perichaetial leaf form is also useful in distinguishing between D. robustum and D. billardierei.

Dicranoloma dicarpum, D. fasciatum, D. platycaulon, D. plurisetum, and D. obesifolium are characteristically white-green and quite dull in appearance when fresh. Their colour is suggestive of, but less pale than, that of a Leucobryum. B. Macmillan (pers. comm.) aptly describes it as "milky". Once the characteristic colour and dullness of these plants is recognised, it is usually easy to spot even relatively small cushions of the white-green species in the field, and their fresh coloration is useful to distinguish them from sterile plants of D. robustum, which in its representative form is the most abundant and conspicuous Dicranoloma species throughout the country. In its terrestrial forms, D. robustum is usually yellow-green in colour and distinctly shiny.

Although the aforementioned five species cannot be distinguished from each another by colour or sheen, there are numerous characters, some readily observed in the field, that permit their separation. The dimensions (or l:w ratios) and apical form of vegetative leaves, the nature of leaf areolation, the strength of the leaf border, the nature and degree of toothing of the upper leaf, the nature of spines on the abaxial surface of the costa, the relative length of perichaetial leaves to the mature sporophytes, and the number of sporophytes per perichaetium all provide characters useful to define or identify N.Z. species.

The sexuality of all Dicranoloma species is dioicous, with the ♂ plants nearly always dwarfed and epiphytic on ♀ or sterile plants. Ramsay (1985) investigated the cytological and physiological relationships between ♂ and ♀ plants in Dicranoloma. Non-dwarf or "free-living" ♂ plants have also been recorded from D. billardierei, D. dicarpum, D. fasciatum, and D. menziesii (Ramsay 1985; Klazenga 2003).

Dicranoloma billardierei can be difficult to distinguish from D. robustum in the herbarium. However, in the field, D. billardierei is distinguishable by its more conspicuously branched upper stems, shorter leaves, and pale yellow-green coloration. There is a subtle flattening of the leaves in fresh material of D. billardierei, which make its branched, red-brown stems much more conspicuous than the mostly unbranched stems of D. robustum.

Dicranum diaphanoneuron Hampe & Müll.Hal. [Linnaea 36: 515 (1870)]. There is no substantive evidence that this species occurs in N.Z. Dixon (1913, p. 13, as Dicranoloma) quoted Brotherus in saying that it is known from "Victoria, Tasmania, and New Zealand". However the type specimen is from Western Australia, as are most of the collections cited by Klazenga (2003), who makes no mention of this species occurring in N.Z. This species is not discussed further here.