Plant of the Week – 19th April 2021 – Calloria neglecta

Introduction

With the arrival of spring, plants are rapidly pushing out their new season’s leaves and shoots to make the next few months a period of exciting change; the challenges of the pandemic makes this slow-motion explosion of green renewal even more welcome.

But don’t be too hasty to overlook last season’s long-deceased plant remains because some will be taking advantage of those resources. Dead leaves and stems are a wonderful nutritional smorgasbord for those with the right tools (enzymes such as cellulase) to break down the complex ‘building-blocks’ of plants.

So as the temperatures rise and plants put on their new season outfits, a whole host of fungi are actively recycling last season’s discarded plant material. There are hundreds of identifiable fungi species to be found, some distinctive enough to be identified with just a hand lens, and others that are so characteristic they are recognisable from several paces.

Calloria neglecta is without a vernacular name but that does not detract from the ease of finding it nor its identification. Calloria neglecta has a preference for the upper portion of dead nettle stems, above the rapidly growing nettle shoots coming up from below, so if it is in your nettle patch, its presence should be apparent.

Each individual ‘fruit body’ is very small, no more than 1 mm wide; however, as each one grows with others in discontinuous patches, they are collectively easy to see.  In a dried state, these patches form a thin deeper-orange crust that can be partially immersed within the nettle stem.

Fig 1. Orange collectives of Calloria neglecta (dried) visible on the stem on the left.
Although not discussed in this article, the stem on the right has a very large number of black Mycosphaerella superflua, another frequent fungus on Urtica dioica.

When moistened, within minutes each Calloria expands into a small dish (for those familiar with fungi, a ‘discomycete’). This rapid response to moisture is an adaptation to the harsh unpredictable conditions of the exposed upper portion of the nettle stems; Calloria neglecta can withstand repeated drying and wetting. Hydrated Calloria patches lighten in colour (see photos below).

When hydrated, it is from the concave surface of the ‘dish’ that Calloria produces spores within fluid filled tubes; termed asci (singular, ascus). As the spores mature, the fluid within each ascus increases so when an opening develops in the ascus tip, this internal pressure forces the ascus contents, including the spores into the open air.

Fig 3. An ascus of Calloria neglecta.  It’s not quite mature so it does not yet contain spores; it is surrounded by
sterile filaments. The red tint within the image is a microscopy stain and not the colour of the fungus. Magnification x1000.

Next time you’re on your botanical walk and you come across a patch of nettle, with dead stems upright amongst the green shoots emerging up from the ground, take a few moments to examine the stems of last year’s nettle for your own miniaturised squashed tangerines.

Further Reading

The essential manual to these smaller mycological wonders is Microfungi on Land Plants; An Identification Handbook by Martin B. Ellis & J. Pamela Ellis. This book is an essential guide to anyone wishing to identify smaller fungi, and pages 440 – 444 (1997 enlarged 1997) describes the many species found on Urtica.

Cameron Diekonigin

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