Pachyphloeus Melanoxanthus a Rarely Collected Hypogeous Fungus

Pachyphloeus Melanoxanthus a Rarely Collected Hypogeous Fungus

Vol 14 (3) Pachyphloeus melanoxanthus a rarely collected hypogeous fungus Caroline Hobart* he genus Pachyphloeus is rarely recorded; ascocarps are hy...

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Vol 14 (3)

Pachyphloeus melanoxanthus a rarely collected hypogeous fungus Caroline Hobart* he genus Pachyphloeus is rarely recorded; ascocarps are hypogeous and therefore difficult to find. There are thirteen species described worldwide to date. According to Pegler et al. (1993) and Hawker (1954) we have three species in the UK, and these account for thirty records in the FRDBI (most are 19th century and some are duplicates). Pachyphloeus conglomeratus has just two substantiated British records, both from Gloucestershire: the type, collected by Broome in 1848 and a second collected by Lillian Hawker in 1950. P. citrinus was said to be unknown in Britain since 1848 apart from a possible immature collection from Bristol in 1951, and a further record from the Forest of Dean in 1986, recently added to the database. I have made four collections fitting its description since 1995, in Yorkshire, Derbyshire, Nottinghamshire, and the Forest of Dean. Splits of these collections are lodged at Royal Botanic Gardens, Kew. Unpublished DNA sequences obtained by Rosanne Healy and Martin Bidartondo show that these collections comprise two species; we are sure that one of these is undescribed.

The third species Pachyphloeus melanoxanthus has been recorded eleven times, six with material at Kew substantiating them. All but two of these records are from the 19th century; most were collected between 1843 and the 1870’s, in the south west of England (Devonshire, Wiltshire, Gloucestershire and North Somerset). Not having been collected in the 20th century, the species was believed to be extinct (Pegler et al., 1993). Two recent records were from the Forest of Dean, supposedly collected by Dave Jefferies and Innes Jelly in 1986. Dave is unable to confirm these records, believing them to be a recording error and confused with the collection of Pachyphloeus citrinus, now in Kew, which they made that day. I therefore believe that the collection described below is the first in the UK since 1878. It was found just under the leaf litter at Abney Clough, Derbyshire on 10 Aug. 2011, but was then immature. I returned on 31 Aug. 2011 and more mature material was collected from the same spot under a large old beech with nearby hazel.


Brief description based on collection of 31 Aug. 2011 For a fuller description of this species see Pegler et al. (1993). Pachyphloeus melanoxanthus (Tul. & C. Tul. ex Berk.) Tul. & C. Tul. Ascoma 7.5–9 mm, globose to slightly flattened, black. Surface covered with low warty projections composed of small papillae (Fig. 1). Lower surface with umbilical hollow exposing the gleba, this with short hair- like hyphae protruding from it. Ascoma attached to root. No discernible smell. Peridium black, with narrow warty cortex, outer layer composed of thick walled red - brown cells merging into a pseudoparenchymatous layer. Cell walls thinning toward the interior eventually merging into the gleba. Gleba hyaline composed of a gelatinous matrix of small globular cells, with yellow veins radiating

Fig. 1. Ascoma of Pachyphloeous melanoxanthus showing peridium composed of small papillae. Photograph © Caroline Hobart.

*84 Stafford Road, Sheffield, South Yorkshire S2 2SF



Vol 14 (3) and contradicts their own description which is similar to that of Pegler et al. (1993). Spores of the described Italian material are illustrated, and show irregular truncated short warts; they are described as having the remains of a perisporium which can be seen in their photograph. P. melanoxanthus, as described from the holotype, has clearly visible long tapering spines, which in some cases are truncated. There is no mention of a perisporium, or evidence in my material of one, unlike P. citrinus. Rosanne Healy has studied the holotype and my material and she and I believe my material is indeed P. melanoxanthus. There is one uncertainty, and that is the ascus wall, described in Pegler et al. (1993) as “not stained in Melzer’s reagent”. My material is weakly amyloid. It seems likely that this reaction has been missed in earlier descriptions of P. melanoxanthus. Some other Pachyphloeus species are known with more strongly amyloid ascus walls.

Fig. 2. Sliced ascoma showing typical umbilicate basal hollow and yellow veins in hyaline gleba. Photograph © Caroline Hobart.

Collections examined England, Derbyshire, Abney Clough, hypogeous near Fagus sylvatica 10 Aug. 2011 and 31 Aug. 2011, CA Hobart K(M) 173681; W. Sussex, Eartham Wood under Fagus sylvatica, 11 Nov. 2012, M. Waddingham. The last of these, received after this note was drafted, was extremely small, but had more mature (darker) spores than my collections.

Fig. 3. Asci containing globose spores with blunt spines. Photograph © Caroline Hobart.

from the umbilicate hollow (Fig. 2). These veins appear as a strong yellow smear in a squash using water. Asci 140 x 40 µm, walls when mature only very weakly amyloid even when pre-treated in 5% KOH which normally enhances the amyloid reaction. Immature ascus content dextrinoid. Ascospores globose, 15–19 µm including ornamentation, with large oil drop; spine tapering, with truncated or rounded ends 3.5–4 µm long when mature (Fig. 3).

Acknowledgements With thanks to the following individuals: Rosanne A Healy for help with the identification and discussions, Martin Bidartondo for the DNA analysis of my Pachyphloeus collections, Brian Douglas for interpreting the data and Melissa Waddingham for allowing me access to her material.


Comment When I examined these collections, I naturally consulted the references cited here. I was fairly certain that I had collected P. melanoxanthus, but the photograph in Montecchi & Sarasini (2000) bore little resemblance to the description in Pegler et al. (1993) or to my material. The gleba is described in the Kew volume as “yellow to olive becoming blackish brown “, whilst in the illustration in the Italian volume it is clearly pink

Hawker, L., (1954). British Hypogeous Fungi. Phil. Trans. Roy. Soc. Lond. ser. B. Biological Sciences 237: 429–546. Montecchi, A., & Sarasini, M. (2000). Funghi Ipogei d’Europa. AMB. Pegler, D.N., Spooner, B. M., & Young, T.W.K. (1993). British Truffles: Revision of British Hypogeous Fungi. Royal Botanic Gardens, Kew.