Acarospora Benedarensis: a Rare Terricolous Maritime Lichen from Ireland, Scotland, and Wales

Opuscula Philolichenum, 9: 31-34. 2011. Acarospora benedarensis: a rare terricolous maritime lichen from Ireland, Scotland, and Wales 1 2 KERRY KNUDSEN & HOWARD FOX ABSTRACT. – Acarospora benedarensis, a rare terricolous lichen endemic to Ireland, Scotland and Wales, is discussed. It is recognized as having a much higher hymenium than described in the protologue with correspondingly tall asci. It is probably not a member of the new genus Silobia but further study of its systematic position is needed. A lectotype is also designated. KEYWORDS. – Acarospora rhizobola, biological soil crusts, hypothallus, maritime lichens, morphology, nitrophiles, rhizohyphae, Silobia rhagadiza, taxonomy. INTRODUCTION In 1913, in “The Maritime and Marine Lichens of Howth” in the Scientific Proceedings of the Royal Dublin Society, Matilda C. Knowles described Acarospora benedarensis M. Knowles from Howth Head in Ireland near Dublin. The species is rare in nature (Fletcher et al. 2009). While studying at the United States National Herbarium (US), the first author found a small but excellent specimen of A. benedarensis collected on Howth Head by Knowles and originally given to the American lichenologist C.C. Plitt. The mature apothecia were well developed as was the thallus, allowing for some new observations. The current description (Fletcher et al. 2009) is adequate for identification, except for hymenial height, which in mature apothecia is much higher, and ascus size is lacking. DISCUSSION Knowles discovered Acarospora benedarensis on lower “earth banks” of white fine clay forming steep lower slopes along the cliffs on the southwest coast of Howth Head. The distinct white soil type of Howth Head is Hippy Hole Formation sediments of Cambrian origin (van Lunsen & Max 1995) and this habitat is exposed to salt spray. She further described the community in which A. benedarensis occurs as follows (Latin names for plants inserted from Doogue et al. 1998): “Scurvy-grass (Cochlearia officinalis L.), Sea Spurry (Spergularia rupicola Lebel ex le Jolis), Sea Lavender (Limonium humile Miller), Thrift (Armeria maritima (Miller) Willd.), Plantains (Plantago coronopus L. and Plantago maritima L.) and Sea Campion (Silene uniflora Roth) are abundant. Bare patches of ground, sometimes of considerable area, occur here and there by the paths, and among flowering plants. The soil seems to be derived chiefly from the disintegration of very friable and finely laminated shales, masses of which crop out above the surface in many places. It is a stiff, almost white clay, very powdery in dry weather, and very sticky and close in wet weather. These apparent bare patches are covered with a kind of broken skin formed of crustaceous lichens, grey, green, yellow, black, and brown, all mingled together in some places, but in others forming large colonies of pure growth.” (Knowles 1913). Acarospora benedarensis was “one of the most abundant lichens” in these biological soil crusts in “the driest and sunniest locations” often forming large, continuous, and exclusive patches. The thallus of A. benedarensis is an aggregation of areoles, 1-3 mm in diameter, of various shades of brown, powdered with 1 KERRY KNUDSEN – The Herbarium, Dept. of Botany & Plant Sciences, University of California, 2117 Batchelor Hall, Riverside, CA 92521, U.S.A. – e–mail: [email protected] 2 HOWARD FOX – National Botanic Gardens, Glasnevin, Dublin 9, Ireland – e–mail: [email protected] 31 white soil in the specimen the first author examined. Some of the areoles are subsquamulose with a distinct lobulation along the edges though they remain broadly attached. The apothecia are easy to see after wetting the areoles. They have dark concave discs in usually distinct raised parathecial crowns, one or more per areole. The cortex is distinctly paraplectenchymatous. The algal layer is not consistently interrupted by hyphal bundles and only one bundle was observed in the specimen studied. Magnusson (1929) too reported it as a variable character. The hymenium was described in the protologue as 100 μm high and no measurements were given for the asci (Knowles 1913). The original measurement must have been based on an immature hymenium and has been repeated from the protologue rather than observed by later writers (e.g., Roux 2007). The first author observed hymenial heights of 180-200 μm in a mature apothecium with asci 150-160 x 20 μm which were not fully matured. Magnusson (1929) also observed a high hymenium, up to 170 μm high. The paraphyses are thin, mostly 1-1.5 μm in diameter, with infrequent branching. The ascospores are mostly 3-5 x 1.5 μm, subglobose to broadly ellipsoid. The first author saw few mature ascospores himself. The areoles lack a true lower surface and the medullary hyphae are continuous with an endosubstratal hypothallus composed of both thin hyphae and thicker, distinctly anastomosing rhizohyphae. The hypothallus gives rise to new areoles that are closely spaced. This type of hypothallus is common among terricolous Acarospora A. Massal. and occurs for instance in the cosmopolitan A. schleicheri (Ach.) A. Massal. (Knudsen 2007) as well A. fuscescens H. Magn. (Knudsen 2008), A. thelococcoides (Nyl.) Zahlbr. (Knudsen 2007), and A. orcuttii K. Knudsen (Knudsen 2010) in western North America. These species are obligatory terricolous crusts and only a few populations have been found on disintegrating soft rock that allows the development of the extensive hypothallus. Knowles (1913) wrote an excellent description of the hypothallus of A. benedarensis: “It is a very efficient earth-builder. The undersurface of the thallus has no defining layer, and the hyphal filaments penetrate the fine powdery soil, ramifying and branching in all directions, and enclosing particles of soil in their tissue.” Acarospora benedarensis is endemic to Ireland, Scotland and Wales. Fletcher et al. (2009) reported it from Howth Head as well as the Welsh Islands (Angelsey and Bardsey) and Scotland (Angus and Orkney). It had been reported prior to 2000 near the Blasket Islands off western Ireland (Davey 2008), but this may be a misidentified Silobia M. Westb. & Wedin with norstictic acid. Clearly the species is rare. Fletcher et al. (2009) reported it occurs on clay “compacted by sheep-trampling and on the floor of recesses used by them for shelter” in Wales. It is likely that A. benedarensis is a nitrophile and is being fertilized by the sheep. It appears to be more successful in disturbed terricolous habitats than most terricolous Acarospora, which are easily extirpated by disturbance (Knudsen 2010; Knudsen et al. in rev.). Knowles never mentioned sheep at the type locality or in connection with the species, and there are no sheep on Howth Head. Acarospora benedarensis was considered part of the A. smaragdula complex by Clauzade and Roux (Clauzade et al. 1981) and was recognized as one of many varieties of A. smaragdula. Roux (2007) recently recognized it as a distinct species, apparently still considering it part of the A. smaragdula complex. During the recent revision of this group (Westberg et al. 2011; Westberg & Wedin 2011), which led to the recognition of the new genus Silobia, modern specimens of A. benedarensis were not available for sequencing and only a poor type specimen was seen. Westberg et al. (2011) speculated it might be a synonym of Sarcogyne rhagadiza (Nyl.) M. Westb., the name applied to the taxon previously included in A. amphibola Wed. by Magnusson (1929). The presence of a hypothallus suggests that A. benedarensis does not normally occur on rock while S. rhagadiza does. Acarospora benedarensis also has a higher hymenium than S. rhagadiza (180-200 µm vs. 110-160 μm) with taller asci (150-160+ µm vs. 105 μm) (Westberg et al. 2011). Both species occur in the same maritime habitat in Ireland according to Knowles (1929). Above the high tide level A. benedarensis grew especially on cliff tops and steep earth banks though it was still exposed to salt spray. Silobia rhagadiza (treated as A. amphibola by Knowles) was “not uncommon on schistose rocks, within reach of the waves, at the base of the earth cliffs, Stella Maris and Broad Strand, Howth, 1911”. Acarospora benedarensis should not be considered a member of Silobia until an analysis of molecular data has been performed to confirm its position in the genus. Based on a morphological analysis, the only characters it shares with the genus Silobia are narrow paraphyses and a high hymenium. These characters are not restricted to Silobia though they are elements of its unique suite of characters. Acarospora benedarensis apparently lacks a distinct and consistent interrupted algal layer, a character occurring in all Silobia species. Nonetheless, other specimens should be checked for an interrupted algal 32 layer, possibly developing in older areoles. Interrupted algal layers do occur in other Acarospora species, for instance A. cervina A. Massal. or A. badiofusca (Nyl.) Th. Fr. s. lat. from central Europe. Conidia (4-5 x 1 µm) were observed in Acarospora benedarensis, confirming the report of long conidia in the protologue (Knowles 1913). This is not a common conidium size in Acarospora. Interestingly the high hymenium and long conidia are shared with two other terricolous Acarospora with rhizohyphae, A. rhizobola (Nyl.) Alstrup (Fletcher et al. 2009) and A. terricola H. Magn. (Knudsen 2007). Acarospora rhizobola is a member of the Acarosporomycetidae but is only distantly related to Silobia (Westberg, pers. comm.) based on molecular data. Acarospora terricola also has scattered hyphal bundles penetrating the algal layer that can only be easily seen in mature specimens (Knudsen 2007). The etymology of the name has Ben Edair, the Irish name for Howth as its basis. This name is well known to Dublin commuters and is attested on the front of Dublin buses on a bilingual caption showing the destination of bus routes 31 and 31B which runs many times daily from the city centre. Here we select a lectotype from five boxes of specimens (3 types) collected by Knowles on a single sheet at the herbarium of the Dublin National Musuem (DBN).

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