Type: Tahiti. [State or Province unknown]: ad corticem arboris, 1868, Leclerc de Buffon, G.C. or Vieillard, E. s.n. (lectotype – H!, designated by Hale & Fletcher 1990; paralectotype– H!).
Description.Thallus corticolous, rarely saxicolous; uppersurface white to whitish gray, dull to shiny, epruinose or pruinose, densely reticulate-maculate, often cracked; abundantly sorediate; soralia capitate, conspicuously stalked, at the tip of distinct, short to elongate, laciniate lobes (clavulae); soredia farinose to ± granular, surface creamy white, typically not discolored; lobes moderate-sized to large, broad, 2–6(–10) mm wide, ± angular, abundantly ciliate; cilia short and slender, 0.3–1.5 mm long, black, mostly simple, very rarely branched; lowersurface often blackened throughout, the rhizines growing close to the lobe margin, but some lobes typically with a deep brown, erhizinate, ~ 1–2 mm wide margin, particularly the elongate laciniae typically erhizinate and bright white below, lacking pigmentation; rhizines, where present, long, slender, black, mostly simple, rarely sparsely branched; medulla white. Apothecia and pycnidia not observed among the Galapagos specimens.
Ecology and distribution. Oceania (Lamb 1963; Feuerer 2008; Spielmann 2009), Asia (Feuerer 2008; Ohmura et al. 2012; Ahn & Moon 2016), Hawaii (Moon et al. 2001), Brazil (Barros & Xavier Filho 1972; Jungbluth 2006; Benatti & Marcelli 2008; Spielmann & Marcelli 2009). Previously reported only online (Bungartz et al. 2016); a common and abundant species, from the dry zone through the transition and humid zone into the high altitude dry zone; most abundant within the transition and humid zone; most frequently on bark, wood or cactus pads, often on twigs or branches of both native and endemic and introduced trees and shrubs; occasionally on rock, typically at sunny and exposed sites. The typical morphotype with long ‘clavulae’ is the most common one, but a second morphotype (see below) apparently does not differ in habitat preferences.
Notes. A corticolous, sorediate species with a gray reticulate-maculate surface and salazinic acid in its medulla; usually easily recognized by its clavulae, i.e., the distinctly stalked, capitate soralia protruding from long, slender, laciniate lobes. In some specimens the surface is heavily pruinose; others have a shiny, epruinose cortex. The characteristic reticulate-maculae are not always easily seen in these shiny or heavily pruinose specimens and can often only be distinguished upon closer inspection. Although some authors do not recognize this taxon as distinct from P. reticulatum s.str., the Galapagos specimens are easily distinguished already in the field. Parmotrema clavuliferum does not only form distinct clavulae; these laciniate lobes are also characteristically unpigmented below, the lower side of the lobes subdividing into clavulae with a mottled appearance of white, unpigmented areas towards their tips, brown pigmented areas further below, eventually blackened towards the thallus center. Whereas the clavulae of P. clavuliferum always lack rhizines, the broad lobes of P. reticulatum are typically densely rhizinate even close to the margin; these lobes often lack the broad erhizinate margin otherwise so typical for this genus. Here we consider these two taxa, P. clavuliferum and P. reticulatum, as distinct, well distinguished, separate species, especially since a recent study by Ahn & Moon (2016) found molecular support for this opinion. Our experience suggests that specimens with less conspicuously stalked but nevertheless capitate soredia also deserve attention. With P. clavuliferum and P. reticulatum s.str. they share the same chemistry (cortex with atranorin, medulla with salazinic acid), but their capitate soralia are morphologically closer to P. clavuliferum, and these short clavulae also share a mottled white-brown blackened lower lobe side. We have provisionally treated them below as morphotypes – P. clavuliferum with long vs. short clavulae. In Brazil, material commonly identified as P. clavuliferum is morphologically also rather heterogeneous (e.g., Benatti & Marcelli 2008) and it has be argued that some of these specimens may constitute a separate species (Spielmann 2009). Almost all collections of P. clavuliferum in the Galapagos are corticolous. Only one specimen has been found on rock (Spielmann 10450, CDS 51806). The species shares many characteristics with P. marcellianum, which grows exclusively on rock and generally has much smaller lobes.