Chemical divergence of eastern North American and European populations of Arctoparmelia centrifuga and their sympatric usnic acid-deficient chemotypes

Usnic acid-deficient thalli of the lichen Arctoparmelia centrifuga (L.) Hale, previously known only from Fennoscandia, are reported here from New Brunswick and Newfoundland. Pigment-deficient and pigment-containing thalli growing side by side in New Brunswick show no detectable differences in morphology, reproductive state, or lichenicolous microfungi. The Fennoscandian and eastern Canadian populations of typical A. centrifuga contain different combinations of unidentified fatty acids. Their respective usnic acid-deficient counterparts are similarly distinct, providing strong evidence that the pigment-deficient chemotypes originated separately on the two continents, rather than from a common ancestor. Among a collection of saxicolous lichens which I made in northern New Brunswick, Canada, in 1984 is a specimen identical in morphology to the circumpolar, boreal-arctic species Arctoparmelia centrifuga (L.) Hale, but which lacks the yellow cortical pigment usnic acid. Usnic acid-deficient chemotypes ofA. centrifuga have been reported previously only from Norway, Sweden, and Finland (Hasselrot 1953; Poelt and V6zda 1981; Santesson 1984) and have been recognized at various taxonomic ranks, from forma to species, as follows: Parmelia centrifuga var. dealbata Fr. , Summ. Veg. Scand. 103. 1845[1846], nom. nud. Parmelia centrifuga # dealbata Fr. ex Th. Fr. , Lichenogr. Scand. 1: 129. 1871. TYPE: Sweden, Nirke, G8tlunda parish, Hasta, 1863, Blomberg, ups, holotype, not seen; CANL, H, topotypes! ("1865 & 1866, Blomberg"). Parmelia centrifuga # dealbata Th. Fr. ex Hellbom, Nerikes lafflora, 16. 1871, not seen. Parmelia centrifuga fo. dealbata (Th. Fr. ex Hellbom) Hillmann, Ann. Mycol. 24: 142. 1926, not seen. Parmelia aleuritica Nyl. , Flora 58: 103. 1875. TYPE: Finland, Padasjoki [= North Hime: Pihlajavesi, fide T. Ahti, in litt. ], 1874, Norrlin 244, H-NYL 34674, holotype! ; H, isotype! (Herb. Lich. Fenn. 204). Parmelia centrifuga fo. aleuritica (Nyl.) Oliv. , M6m. Soc. Sci. Nat. Cherbourg 36: 182. 1907. Arctoparmelia aleuritica (Nyl.) Hale, Mycotaxon 25: 252. 1986. Hale (1986) created the genus Arctoparmelia to accommodate the distinctive "Parmelia centrifuga group" and recognized A. aleuritica as "an usnic acid-free mutant of A. centrifuga"--one of five species in the genus and the only one lacking usnic acid in the cortex. As the nomenclatural history of this lichen shows, the epiphet aleuritica also has priority at the rank of forma. Hale did not state explicitly his reasons for recognizing the usnic acid-deficient chemotype at species rank, in preference to a lower rank or not at all. While I was investigating the typification and synonomy of this lichen, Teuvo Ahti brought to my attention another eastern Canadian specimen of usnic acid-deficient A. centrifuga, which he had collected in Newfoundland in 1956. I subsequently carried out an analysis of the secondary product chemistry of a number of Fennoscandian and eastern North American specimens of A. centrifuga, using standardized thin-layer chromatography (TLC) 0007-2745/92/1-4$0.55/0 This content downloaded from 157.55. 39.249 on Wed, 03 Aug 2016 06:06:52 UTC All use subject to http://about.jstor. org/terms 2 THE BRYOLOGIST [VOL. 95 (Culberson 1972; Culberson & Johnson 1982). In particular, I cochromatographed the two usnic aciddeficient specimens from Canada with several European collections containing mixtures of usnic acid-containing and usnic acid-deficient thalli. The analyses included an isotype of Parmelia aleuritica Nyl. and a topotype of P. centrifuga (L.) Ach. var. dealbata Fr. ex Th. Fr. , as noted above. OBSERVATIONS ON UsNIC ACID-DEFICIENT A. CENTRIFUGA IN NEW BRUNSWICK Usnic acid-deficient thalli were found on a single boulder of rhyolite tuff and breccia during approximately one hour of systematic general collecting on an extensive south-facing scree slope with patches of stunted Picea mariana-Betula papyrifera-Vaccinium-Cladina heath. An exact count of the number of individual gray thalli was not obtained. A patch (single thallus? ) of irregular outline with a maximum diameter of ca. 10 cm was present along with several smaller discrete neighboring thalli. In the material collected, the thallus lobes are predominantly tightly attached to the substratum; some are intertwined with or overgrowing adjacent thalli of Cetraria hepatizon and typical yellow-pigmented A. centrifuga. There are no apparent differences in the vigour of the gray and yellow thallus forms. Apothecia are well developed in the gray thalli and contain numerous intact asci with a full complement of ascospores. A more detailed description follows. Thallus lobes 0.5-1.8 mm wide, imbricate. Upper surface smooth, mat, "yellowish white" (no. 92; colors according to Kelly 1965) at lobe ends, grading to "medium gray" (no. 265) in older parts [note: slight yellowish tint not due to usnic acid; adjacent typical thalli of A. centrifuga are a contrasting "pale greenish yellow" (no. 104)]. Lower surface minutely roughened, with a few shallow longitudinal wrinkles per lobe, mostly "pale orange yellow" (no. 73); moderately rhizinate, the rhizines simple, to 0.6 mm in length, concolorous with the lower cortex to brownish black (no. 65). Apothecia common in older parts of thallus, to 2.8 mm diameter, deeply concave; thalline margin entire to slightly crenulate; disc dark reddish brown (no. 44). Ascospores 8-12.5 x 4-6 lim. Pycnidia common, conidia weakly bifusiform (bacilliform), with two, less often one, subapical swelling(s), 4-6 x 0.5-0.8 . m. Both yellow and gray thalli are spottily colonized by two unidentified nonfruiting microfungi. One of these has a coarse dendritic branching pattern, each branch comprised of several dark brown parallel hyphae with quadrate to short rectangular cells. The other consists of tiny black hemispherical structures (to 0.2 mm diameter) superficially resembling emergent perithecia or pycnidia. In anatomical section, however, these show no ostiole or other differentiated tissue beneath a thin layer of necrotic, "carbonized" cells. Specimen examined. --NEw BRUNSWICK. RESTIGOUCHE co.: Mount Carleton Provincial Park, north side of Sagamook Mountain, near summit, ca. 710 m; 47*25'N, 66053'W, Clayden 2909 (CANL, NBM).