SYSTEMATIC ACCOUNT ai 



Quite distinct from V. mucosa, the only species with which it may be said to have any affinity, by the 

 much larger and prominent perithecia. It is of interest in being the only known marine lichen which 

 passes its entire existence under water. V. mucosa, hitherto regarded as the most truly marine of all 

 lichens, does not tolerate constant submersion; see in this connexion the remarks of Santesson (1939). 

 V. serpiiloides occurs at the same level as an encrusting calcareous alga {Lithophyllum sp. ?), and forms 

 with it a submarine association just below the lowest ebb-tide level. During the exceptionally low 

 spring tides at Port Lockroy on 2 and 3 November 1944, some of the uppermost patches of the cal- 

 careous alga-Verrucaria serpuloides-association were exposed for a short period^, but at the most 

 extreme ebb I could see the association running down on shelving rocks to a depth of several feet 

 below the surface, where it is certainly never exposed (PI. I, fig. 2). One also finds the association in rock 

 pools left by the receding tide, both the calcareous alga and the Verrucaria consistently keeping below 

 the water level. This is shown in the underwater photograph PI. II, fig. i, in which the Verrucaria is 

 seen as a black band the upper edge of which coincides exactly with the surface of the water in the pool 

 when the latter is left at ebb tide. This clear-cut upper limit is an indication that the submarine habitat 

 in V. serpuJoides is obligatory and not facultative. 



Verrucaria tesselatula Nylander (Fig. 3^; PI. IV, fig. 9) 



apud Crombie, 1876, p. 191; Miiller (Arg.), 1889, p. 172. 



Verrucaria dermoplaca Nylander, apud Crombie, 1876 a, p. 234 (vide infra). 



Verrucaria glaucoplacoides Darbishire, 1912, p. 18, pi. 3, figs. 34, 35; Cengia Sambo, 1926, p. 23. 



South Orkneys. Inaccessible Islands: on schistose rock (non-calcareous); Discovery 193 1-3, 

 25- i- 1933 (nos. 1094-1, 1094-2). 



Comparison of the holotype of Darbishire 's V. glaucoplacoides from East Falkland with a syntype 

 of Nylander's V. tesselatula from Kerguelen (in herb. Kew) showed them to be identical. This 

 species is closely related to V. ceiithocarpa, from which it differs in the lighter coloured thallus with 

 larger areolae separated by gaping black cracks. Darbishire 's photographs (loc. cit) show the habitus 

 well. The following data are derived from the syntype specimen from Swain's Bay, Kerguelen, coll. 

 Transit of Venus Expedition, 1874-5. 



Thallus o- 1 5-0-20 mm. thick, even, tesselate-areolate with plane, angulose areolae 0-5 i-o mm. diam. 

 separated by conspicuous black cracks about 0-15 mm. wide; matt, not pruinose, pale buff-brovm. 

 No basal fuhginous layer. Gonidial algae subglobose, 9-1 5 /< diam., with a slight tendency to form 

 vertical rows in the thallus; ± bright green, muhiplying by binary fission, so that two are often seen 

 together in the same sheath, as mentioned by Nylander. Perithecia numerous, 1-6 in an areola, up to 

 0-2 mm. diam., with the black convex apex (involucrellum) rising slightly above thallus level, matt or 

 slightly shining, not impressed or papillate, with very minute ostiole. Excipulum globose, immersed, 

 165-180// diam., with colourless wall. The involucrellum, brown-blackish in section, forms a dome- 

 like roof over the upper part of the excipulum. No paraphyses. Asci clavate, about 40 x 12//, with 

 indistinct gelatinized walls. Spores about 11 ■: 7// (10-15 x 7-8// according to Nylander). 



The specimens from East Falkland agree well with the Kerguelen type. The specimen from 

 Tierra del Fuego, Ushuaia, coll. Dusen, distributed in ' Lichenes austroamericani ex Herbario Reg- 

 nelUano', no. 377, and also one of the South Orkneys specimens (no. 1094-1) have in places more 

 isolated and less reticulating cracks, leaving small areas of the thallus continuous and unbroken ; they 

 show the first stages of a transition into the extreme state in which the thallus is not areolate, but divided 

 by a loose and irregular network of rhagadiose black-edged cracks into irregular islands of various size. 



1 The parts of the calcareous alga thus exposed subsequently died. 



