Cephalomitrion aterrimum (Steph.) R.M.Schust.
Cephalozia aterrima Steph., Sp. Hepat. 3: 331. 1908.
Herzogobryum aterrimum (Steph.) Grolle, J. Bryol. 11: 326. 1980.
Cephalomitrion aterrimum (Steph.) R.M.Schust., Nova Hedwigia 61: 554. 1995.
Type: Tasmania, Mt. Wellington, Weymouth.
Herzogobryum filarium Grolle, Feddes Repert. 86: 73. 1975.
Type: Tasmania, Lake St. Clair, on lake shore, Scott 574.
[Fig. 128: 3, oil-bodies, p. 558]
Distribution and Ecology : New Zealand: Stewart Island (5 m), South Island ([180]850–1590 m), North Island (1450–1700 m); Australia: Tasmania, Victoria, New South Wales.
In New Zealand known from Fiordland, Otago, Westland, Canterbury, Western Nelson and Volcanic Plateau (Mt. Ruapehu) EPs. In South and North islands a plant of the penalpine and alpine zones, particularly alpine fellfields. Plants typically form compact, flattish to dome-like, thin to rather thick, at times extensive blackish mats over exposed rock or silt of streambeds. Plants typically occur on exposed flat bedrock or over downward, flattish and angling bedrock of creek beds or over small rocks, but in all of these cases Cephalomitrion is found where a thin to thick layer of soil has accumulated (at times ca. 3 cm thick) and where water flow is constant, even if only at a trickle level. The mats lightly adhere to the streambed substrate, or, more often, are firmly anchored to the rock substrate, with slow-moving water flowing over them. Plants are likely to be saturated for all or most of the period that they are not under snow cover. On Stewart Island Cephalomitrion was found at the base of Belltopper Falls (Port Pegasus, immediately below North Arm) at only ca. 5 m in an open, humid niche dominated by bedrock with a forest margin of Weinmannia racemosa and Dracophyllum. In the upper Otira valley (Arthur’s Pass, 870–960 m) on surfaces of greywacke boulders in small stream channels, in penalpine Dracophyllum rosmarinifolium – Chionochloa conspicua shrubland. At Mt. Euclid (Paparoa Ra., Westland, 1280 m) it was on granite stones set in a tarn, surrounded by Chionochloa australis grassland. On the Young Ra. (SE of Haast Pass, Otago, 1150 m) it was on rocks at the side of a cascading snow-melt stream in Schoenus pauciflorus – Chionochloa crassiuscula tussockland. It is most notably found with Isophyllaria attenuata; the two share very similar habitat preferences. Other accompanying species are Allisoniella nigra, Andreaea acuminata, Diplophyllum verrucosum, Ditrichum strictum, Hepatostolonophora rotata, Isotachis montana, Kurzia helophila, Marsupella sparsifolia subsp. childii, Rhacocarpus purpurascens and Siphula decumbens.
Mats are comprised of densely interwoven shoots, and the basal part of the mat often consists of root-like masses of old, dead plant bases that form a mesh that entraps grains of sand and very fine gravel. This appears to provide a notable firmness to the mat that is conducive to withstanding a flow of water after heavy rain or strong snow melt.
The generic description serves to characterize the species.
Comments : Plants have the size, aspect, color, and small, scale-like, bifid leaves of a Cephaloziella, but differ from that genus in the seta, with 8 rows of outer cells and 4 rows of much smaller internal cells; Cephaloziella has a seta of the 4+4 type. Several vegetative differences between the genera are useful. Plants of Cephalomitrion appear leafless due to the erect and markedly appressed leaves vs. moderately to widely spreading and distinct in Cephaloziella. Cephalomitrion also differs in stem anatomy, with a somewhat differentiated cortex of 1(2) strata of relatively thin-walled cells, distinct from the many rows of smaller, notably thick-walled, medullary cells each with a small lumina. Cephaloziella has stems with a cortex of firm-walled cells and medullary cells thinner-walled. Cephalomitrion lacks gemmae whereas they are typically present in Cephaloziella. Also, the leaf cells in Cephalomitrion tend to be clearly gibbous, especially near the margins.
Schuster (1996a, p. 14, 47) used the name Cephalomitrion aterrimum var. longiscyphum, nom. nud. for a plant from Tongariro Natl. Park. We have not seen the specimen.
