Jeremy Bartlett's LET IT GROW blog

Last month I had a pleasant surprise when I watered a plant in our conservatory. Three fungal fruitbodies were emerging from the compost of some rooted cuttings I had potted up in peat free compost late last summer (note 1).

The caps were pale buff or ochre at the centre, fading to white around the edges, and were only just above the level of the compost (although they grew a bit taller after a few days). In both colour and build they looked rather like fieldcaps (Agrocybe sp.).

I picked one of the fruitbodies to look at its underside.

The gills were crowded and pale brown and the stem was white and pruinose (note 2). The fruitbody had a faint, earthy smell.

I looked at the spores. They were ellipsoid-ovoid in shape, thick-walled and lacked an obvious germ pore (note 3).

Agrocybe spores have a distinct central germ pore. In addition, the spore size just didn’t fit with any of the species of Agrocybe I was aware of.

I took a look at the cheilocystidia, the cells that project from the gill edge.

They had the distinctive lecythiform form (described as “skittle-shaped” or “bobble-capped”) found in the genus Conocybe.

The caulocystidia (cells projecting from the stem) were of a similar shape.

The fungus matched pictures and descriptions of Conocybe intrusa in my books (note 4) and on various websites, such as www.pharmanatur.com and in the gallery on the Global Biodiversity Information Facility (GBIF) website. The English name of the fungus is Hothouse Conecap, which is very appropriate, given where it is usually found.

The only other known occurrence of Conocybe intrusa in Norfolk was at Gresham’s School in Holt in North Norfolk, when Tony Leech found the fungus growing in a pot of Angel’s Trumpets (Brugmansia) in a greenhouse.

Tony collected his first specimens of Conocybe intrusa on 21st April 2002 and kept them to show to Alick Henrici at the spring conference of the British Mycological Society (BMS). Alick had seen a single fruitbody of the same species (an “outwardly featureless brown-spored agaric”) growing in a temperate ferns bed in the Princess of Wales Conservatory at Kew on 27th April 2002. Both examples had the very characteristic lecythiform cheilocystidia of Conocybe. Alick subsequently wrote about Conocybe intrusa in “Notes and Queries” in the BMS journal Field Mycology (note 5). More fruitbodies appeared with the Gresham’s School Brugmansia in June 2005 and Tony recorded them on the Norfolk Mycota.

Watling (note 4) describes Conocybe intrusa as “obviously introduced” and Alick Henrici says it is an alien from North America, which is where it was first found. The GBIF website lists 187 occurrences of the fungus from North America and Europe.

Concocybe intrusa has a much chunkier build than other British species of Conocybe (such as Golden Conecap, Conocybe aurea, that I wrote about last November). It’s not surprising that it was originally named Cortinarius intrusus by the American mycologist Charles Horton Peck (1833 – 1917). It was one of 2,700 new species Peck identified in the course of a 48 year career. (Like me, Tony Leech initially thought “Agrocybe?”.)

Alick Henrici cites “an excellent illustrated write-up recently in Mycologist” but unfortunately this is behind a paywall, out of reach to mere mortals (note 6). The write-up lists finds in Surrey in 2000 (plant pots in a cold greenhouse and indoors on Arthur Bowers ‘New Horizon’ peat-free compost), at Edinburgh Botanic Gardens (1958), at Kew (1967, 1978), in Somerset (1980 in manured garden soil) and in Shropshire (1997 in pots). Alick Henrici concludes “That adds up to four records in 40 years followed by four more in the last five. Either it or our awareness of it is on the increase. Nearly all these records were in spring.”

At the time of writing twenty records are listed on the Fungal Records Database of Britain and ireland (FRDBI) and the fungus has been found in many months of the year. Geoffrey Kibby says it is “widespread and frequent” but presumably most finders don’t identify and record it.

This is the current distribution map for the British Isles (which doesn’t include my record):

I was very pleased to find my Hothouse Conecaps and delighted to have identified them.

The fruitbodies lasted several weeks but have now gone but I hope, like the ones at Gresham’s School, the fungi will fruit again some day.

Notes

Note 1 – The plant was a Begonia maculata, an attractive houseplant with white-spotted leaves and pink flowers, which my former next door neighbour, Jean, gave me about twenty-five years ago. The plant is easy to grow and propagate. I take cuttings every few years, root them in a vase of water and pot them up once they’ve formed roots. I use them to replace the parent plant when it has grown too big.

Last summer I used two types of peat-free compost: several bags of Sylvagrow multi-purpose peat-free compost and a small bag of RocketGro seed and cutting compost with John Innes. Annoyingly, I didn’t make a note of which compost I used for the Begonia cuttings, but I’m pretty sure it was the “Sylvagrow”. It seems to be a good medium for fungi – I’ve previously seen pots of it growing the lovely Wrinkled Conecap, Pholiotina rugosa at Natural Surroundings in North Norfolk.

Note 2 – Pruinose: “covered with a bloom (like a fine layer of chalk dust), similar to that seen on black dates”. (Definition from the books “Mushrooms and Toadstools of Britain and Europe”, by Geoffrey Kibby.)

Note 3 – The spore size ranges from 5.0 – 8.0 x 3.5 – 5.5 micrometres.

Ellipsoid = like a collapsed sphere; ovoid = egg-shaped.

The germ pore is a small pore in the outer wall of a fungal spore through which the germ tube exits upon germination.

Note 4 – The books I consulted were:

1. Kibby, G. (2023). “Mushrooms and Toadstools of Britain and Europe, Volume 4”.
2.  Watling, R. (1982). “British Fungus Flora Vol. 3: Bolbitiaceae”. Edinburgh, HMSO. Page 81 and figures 85 – 90.
3. Pages 104 and 105 in Buczacki, S., Shields, S. and Ovenden, D. (2012). “Collins Fungi Guide”, Harper Collins, London.

The latter illustrates the fungus growing on compost beside a plant label and open packet of tomato seeds, which is a nice touch.

I didn’t think the smell was distinctive (faint, earthy). Watling describes it as “slightly radishy or earthy, almost of earth-balls (Scleroderma); Kibby calls it “slightly raphanoid” (radish-like).

Note 5 – Field Mycology, Volume 3 (3), July 2002, page 105. Available online on the Science Direct website.

Note 6 – Moss, M.O. & Jackson, R.M. (2001). “Conocybe intrusa in Godalming, Surrey.” Mycologist 15(4), pages 155-156.