Stereocaulon colensoi C.Bab.
Holotype: New Zealand. Ruahine Range summit. Colenso 2746, BM.
Thallus large, robust, to 8 cm tall, firmly attached at base by a well-developed holdfast and there often conspicuously grooved and longitudinally furrowed with little lateral cracking, branching variable, complex or simple. Pseudopodetia stout, often vertically furrowed, corticate or decorticate, cortex cracked and somewhat marbled, smooth, wrinkled or verrucose-areolate, investing pseudopodetia ± completely to the base, or often restricted to near apices of pseudopodetia in vicinity of the fruit. Phyllocladia corticate, shining, smooth, slightly cracked, terete, finger-like at first becoming branched in older parts, numbers very variable, numerous or sparse. Cephalodia very distinctly stalked, ficoid, often numerous, single or clustered, frequently associated with phyllocladia, large, greyish-blue, surface distinctly convoluted and maculate or areolate-scabrid. Apothecia common, lateral and terminal, disc black or dark brownish- black, to 5 mm wide, immature fruits plane or concave with a conspicuous pale margin, mature fruits consistently convex and immarginate. Hypothecium colourless. Ascospores elongate-fusiform (5-)6-9(-13)-septate, 75-100 × 4-6 µm. Chemistry: Atranorin and colensoinic acid, ± divaricatic acid, ± perlatolic acid.
N: Kaimanawa Ra., Ruapehu, Egmont, Ruahine and Tararua Ras. S: Nelson mountains to Fiordland, Banks Peninsula to Maungatua. St: Mt Allen, Smiths Lookout. Subalpine; in mainly undisturbed sites, from sea level on peat in southern Stewart I., to 2000 m in mountainous areas; on rocks in grassland above treeline, or on rocks in grassland in open river flats at lower altitudes; rarely in shade in forests.
Endemic
S. colensoi is most likely to be confused with some robust forms of S. ramulosum but it differs from this species in a number of important respects: its cephalodia are always distinctly stalked with a wrinkled-scabrid, maculate surface, never smooth; the phyllocladia are predominantly simple or furcate, not coralloid-branched, and their chemical constituents are different. The pseudopodetia of S. colensoi are also, as a rule, shorter and stouter than those of S. ramulosum, and the apothecial discs of S. colensoi are black, whereas those of S. ramulosum, are red-brown. These differences also serve to distinguish S. colensoi from S. argus and S. trachyphloeum.
