A New Circumscription for the Common and Widespread North American Species Physcia Subtilis, and Description of a New Species, P
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Opuscula Philolichenum, 16: 139-152. 2017. *pdf effectively published online 20March2017 via (http://sweetgum.nybg.org/philolichenum/) A new circumscription for the common and widespread North American species Physcia subtilis, and description of a new species, P. thomsoniana THEODORE L. ESSLINGER1 ABSTRACT. – The common eastern North American species Physcia subtilis is shown to be heterogeneous and to consist of at least two distinct species, one of them smaller, with consistently narrow lobes and a top to bottom paraplectenchymatous thallus anatomy, and the other an often larger species, with lobes varying from narrow to considerably broader, and a more typical thallus anatomy with a medulla composed of distinct hyphae. Based on the type material and protologue, the name P. subtilis belongs to the less common, smaller species, and the other taxon is here described as the new species, P. thomsoniana. KEYWORDS. – Eastern North America, macrolichens, Physciaceae, taxonomy, thallus tissues. INTRODUCTION As currently circumscribed, Physcia subtilis Degel. is one of the most common saxicolous members of the genus in central and eastern North America. It has generally been recognized as a highly polymorphic species, and included within its present circumscription are variants from small, narrow-lobed (ca. 0.1 mm wide), closely appressed specimens all the way to much larger, broader-lobed (up to 0.5 mm or rarely even 1.0+ mm wide) specimens which commonly grow loose enough to be easily collected off the substrate (Brodo et al. 2001, Thomson 1963). According to the protologue (Degelius 1940), the thallus of Physcia subtilis is supposed to be composed of paraplectenchymatous tissue from top to bottom, and most subsequent descriptions or characterizations of the species (e.g., Brodo 1968, 2016; Hinds & Hinds 2007; Showman & Flenniken 2004; Taylor 1967; Thomson 1963, 2003; Wetmore 1967) have repeated that feature as characteristic of the species. Early in my studies of the North American Physciae, I was struck by the fact that the wide selection of supposed P. subtilis specimens that I had sectioned over the years all had a rather typical thallus anatomy for a foliose lichen, with a well-organized and delimited upper cortex (paraplectenchymatous in this case), a medulla composed of distinctive hyphae, which are often rather dense and tend to be oriented parallel to the long axis of the lobes, and a well-organized and delimited lower cortex (also largely paraplectenchymatous). This inconsistency between what I expected and what I observed for P. subtilis was mentioned in my paper describing the new species, P. dakotensis Essl. (Esslinger 2004). At that time I had begun to suspect that the original reports of a paraplectenchymatous thallus in Physcia subtilis were based on some type of error, either in sectioning or in interpretation. In an attempt to resolve this problem, I arranged to borrow and study the rich collection (ca. 300 specimens) of material identified as P. subtilis from NY. Based on my study of the NY specimens, as well as many from ASU and KANU, and also restudy of the specimens in my own herbarium, I have concluded that the confusion was caused by the occurrence of (at least) two separate taxa within the present concept of P. subtilis. One of these taxa is less common and less widespread and has small, narrow-lobed and closely appressed thalli which consist totally or largely of paraplectenchymatous tissue. The other taxon is a more common and more widespread species with (generally) larger and broader lobed thalli, which are weakly or not 1THEODORE L. ESSLINGER – North Dakota State University, Dept. of Biological Sciences #2715, P.O. Box 6050, Fargo, ND 58108-6050, U.S.A. – e-mail: [email protected] 139 appressed (and often ascending or mat forming in parts) and which have a well-developed medulla composed of typical hyphae, often rather dense. Based on the protologue (Degelius 1940) and my study of the pertinent type specimens (cited below), it’s quite clear that the name Physcia subtilis corresponds to the former of these two taxa, i.e., the smaller, closely appressed species with a paraplectenchymatous thallus anatomy. The other taxon apparently lacks a name, and is described here as a new species, named in honor of John W. Thomson, in recognition of his pioneering work on North American Physciaceae. Although today John’s treatment (Thomson 1963) of the North American species of Physcia (sensu lato) has become very dated, when published it was one of the very first modern treatments of any major (or minor) group of North American lichens. A full description and discussion for P. thomsoniana is given below and for comparative purposes, a description and discussion is also provided for P. subtilis. MATERIALS AND METHODS More than 500 specimens were studied for this paper, most of which had originally been identified as Physcia subtilis. All were studied in dry condition under an Olympus SZ40 dissecting microscope. The microscopic features were studied and measured in water mounts on a Nikon Alphaphot YS2 compound microscope, sometimes with added lactophenol cotton blue as a dye. Thallus anatomy was studied in nearly all studied specimens of P. subtilis and in a large number of the P. thomsoniana specimens, using free hand longitudinal sections of the lobes and occasionally, whole mounts of the lower cortex in surface view, with upper cortex and medulla chipped away. The habit photographs were taken using the dissecting microscope, with either a Nikon Coolpix 8700 digital camera or a Nikon D7000 digital camera mounted on it. Thin-layer chromatography using three solvent systems was carried out using the standardized methods of Culberson & Kristinsson (1970) and Culberson (1972). For the specimen citations, one specimen from each county was selected for citation. TAXONOMIC SECTION Physcia thomsoniana Essl. sp. nov. MYCOBANK #820032. FIGURES 1 AND 2. TYPE: U.S.A. SOUTH DAKOTA. MINNEHAHA CO.: S edge of Dell Rapids, Dells of the Big Sioux River, 43.81919N, 96.71686W (determined by GPS), elev. 1500 ft., large Sioux quartzite outcrops (flat ground-level and vertical cliffs) along river, riparian deciduous woodland, locally abundant; 11.xii.2015, M.K. Advaita 19303 (KANU!, holotype; herb. Esslinger!, isotype; further isotypes will be distributed in Lichenes Exsiccati Magnicamporum). DESCRIPTION. – Thallus foliose, more or less orbicular to more irregular, moderately to loosely appressed, weakly adnate to more or less loose and easily removed from the substrate, up to ca. 4 or 5 cm in diameter but more often smaller, sometimes coalescing into larger colonies. Lobes elongate and discrete, (0.15–) 0.2–0.5 (–1.0) mm broad, or becoming more flabellate and imbricate or tangled, more or less flat to somewhat convex. Upper surface white to gray-white, very weakly or not maculate, mostly smooth and without pruina. Narrow lobed, adnate thalli often have terminal and/or marginal blastidia formed on peripheral lobes, with or without more blastidia or isidioid granules internally, the broader lobed, imbricate and cushion-forming thalli often have blastidia and more or less abundant coarsely granular soredia on and under upturned lobe ends/edges. Lower surface white to off-white or tan, flat to very weakly concave, sparsely (especially in narrow-lobed thalli) to moderately rhizinate, the rhizines short to more conspicuous and well developed, concolorous with the lower surface or darkening somewhat, simple to sparsely furcate. Thallus (80–) 100–180 (–230) µm thick, medulla well developed and composed of hyphae which are often fairly dense and parallel (in thick sections, sometimes appearing almost like prosoplectenchymatous tissue), lower cortex 10–25 µm thick, distinctly paraplectenchymatous (lumina 3–7 µm, rounded to somewhat angular) and more or less clearly delimited from the medulla, or, composed of paraplectenchyma (lumina 1.5–5 µm) mixed with areas of irregular prosoplectenchyma or with only scattered, intruding hyphae, and then sometimes less distinctly delimited from the medulla. 140 Figure 1, Physcia thomsoniana. A, portion of the holotype, Advaita 19303 (KANU) from South Dakota. B, Dey 5203 (NY) from North Carolina. C, Lendemer 19490 (NY) from Pennsylvania. D, Esslinger 11753 (herb. Esslinger) from Minnesota. E, Esslinger 3493 (herb. Esslinger) from North Carolina. F, Lendemer 6701 (NY) from Missouri. G, Lendemer 24294 (NY) from Pennsylvania. H, Lendemer 24242 (NY) from Pennsylvania. Scales all equal 1 mm. 141 Figure 2. Geographic distribution of Physcia thomsoniana based on specimens examined for this study. Apothecia occasional and sometimes rather numerous, mostly up to ca. 1 mm but occasionally larger, disk more or less flat, black, epruinose, exciple entire or becoming finely crenate, larger apothecia sometimes developing granules or blastidia on the margin; ascospores (12–) 13–17 (–19) × 6–8 (–9) µm, essentially Physcia-type although the lumina sometimes become a bit more rounded. Pycnidia frequent, black and conspicuous, flush to slightly emergent, conidia bacilliform to very weakly bifusiform, 3–5 × <1 µm. CHEMISTRY. – Atranorin, presumably only in the upper cortex. Spot tests: upper cortex: K+ yellow, P+ pale yellow, C-, KC-; medulla: K-, P-, C-, KC-. ETYMOLOGY – Named in honor of John W. Thomson, student of the Physciaceae, my lichenological ‘grandfather’ [i.e., my major professor’s (William Louis Culberson) major professor], and someone who helped many novice lichen enthusiasts, including me, get started working on lichens. ECOLOGY – This species grows primarily on non-calcareous rock in open or somewhat shady habitats, but very rarely it can occur on bark (only a single specimen on bark was seen in this study). DISCUSSION. – Physcia thomsoniana has been confused with, and included in, the concept of P. subtilis ever since the description of that species by Degelius 75 years ago. Although the gross morphology can generally be used to distinguish the two species, it does overlap somewhat, meaning one must rely on their anatomical differences for most small and closely appressed specimens.