RACODIUM ¹

Gintaras Kantvilas ²

Racodium Fr., Syst. Mycol. 3: 229 (1829).

Type: R. rupestre Pers.

Thallus filamentous, black, forming irregular, undelimited tufts or spreading, felt-like mats. Photobiont Trentepohlia, with cells in long chains 10–16(–20) µm wide. Fungal hyphae 1–1.5 µm thick, arranged in a parallel manner and forming a ± regular, rectangular pattern over the surface of the algal cells. Ascomata and conidiomata unknown. Chemistry: nil.

A monotypic, obligately sterile genus. It is identical morphologically to Cystocoleus, which has rather nodulose hyphae of uneven thickness, arranged irregularly over the algal filaments. Superficially similar, filamentous lichen genera such as Ephebe differ by having a cyanobacterial photobiont.

1 Racodium rupestre Pers.

Neues Mag. Bot. 1: 123 (1794).

A bipolar-pantemperate species. In Tasmania, it occupies a similar habitat to Cystocoleus ebeneus, in sheltered clefts and overhangs of rock outcrops and large boulders, but is far less common and is seemingly restricted to higher elevations. The two species may occur together. Observation at high power of the hyphal arrangement is mandatory for distinguishing these two lichens. The filaments of Racodium tend to be darker and more opaque, and observing the hyphae is made easier by eluting water mounts with dilute nitric acid, which gradually clears some of the dark pigment.

Mt Arrowsmith, 42°12’S 146°05’E, 960 m, 1964, G.C. Bratt 1778 (HO); track to Mother Cummings Peak, 41°41’S, 146°32’E, 1000 m, 2002, G. Kantvilas 149/02 (HO); South Sister, lower slope near car park, 41°32’S 148°10’E, 750 m, 2004, G. Kantvilas 427/04 (HO).

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