Urocystis primulicola (bird’s-eye primrose smut)
Bird’s-eye primrose smut, regarded as an extinct British fungus until its rediscovery in 2010, lives concealed inside its pink-flowered host, only attracting attention when it replaces the plant’s seeds with masses of blackish smut spores.
About this species
Smuts are inconspicuous, specialist, microscopic fungi found inside living host plants. They usually remain hidden unless their dark powdery spore masses, characteristic of some species, are noticed in the flowers or other parts of ‘smutted’ plants. Some replace the host pollen with their spores. Others, including several causing important cereal crop diseases and bird’s-eye primrose smut, hijack the seed-producing parts (ovaries) resulting in smut spores instead of seeds. This is a particularly neglected British smut because it only occurs on the scarce, pink-flowered bird’s-eye primrose, Primula farinosa. The smut species found on the yellow-flowered cowslip, oxlip and primrose is now distinguished as U. primulae.
To search for U. primulicola, bird’s-eye primrose seed-pods should be squeezed when the seeds are ripe and ready for dispersal (August or September). This distinguishes the healthy pods (capsules) with seeds from those harbouring the smut as, when squeezed, the latter leave a telltale dark powdery mass of spores on the fingers. The spores should then be checked under a microscope.
Geography & Distribution
Primula farinosa flowering in May in northern Pennines (Image: © Dr A. Martyn Ainsworth)
Urocystis primulicola was originally described on bird’s-eye primrose collected in 1871 in Sweden. It is found across Europe although necessarily restricted to sites supporting its host plant P. farinosa and possibly also the related pink-flowered P. stricta. In Britain, there are only a few historical records and collections and all are associated with bird’s-eye primrose, which is a nationally scarce and Red-Listed plant. It is chiefly found growing in wet limy soils of the northern Pennines. It was collected in 1867 in Teesdale (Durham) and reported at around the same time from the Lake District and, around the turn of the century, in the Malham (Yorkshire) area. The last English record of the smut, until its rediscovery, was with a collection in August 1884 (possibly repeated in 1904) from a bird’s-eye primrose plant in Charles Wolley Dod’s garden at Edge Hall, Malpas, Cheshire. The species was regarded as extinct until rediscovered over a century later after a two-hour search at a site in the Sunbiggin Tarn & Moors and Little Asby Scar Site of Special Scientific Interest in the northern Pennines.
The brownish black spore masses are produced in the primrose ovaries and dispersed, like the seeds they replace, initially from the open end of the seed pod and later from the disintegrating walls of the capsule itself. The spores are aggregated in clusters known as spore balls, measuring around 25-45 x 25-64 µm, which usually comprise up to 15 rounded dark spores (8.0-13.5 x 11.0-18.5 µm) surrounded by a layer of paler sterile cells. Urocystis primulae, now recognised as a similar species sporulating on cowslip, oxlip and primrose (Primula spp. subgenus Primula), is distinguished by its host identity and by its production of larger balls (around 30-60 x 40-90 µm) of larger spores (11-16 x 12-21 µm).
Image: Primula farinosa seed pods showing (left) black spores of Urocystis primulicola coating the central spike-like placenta of the ovary and (right) the contrasting interior of a healthy pod with pale central placenta surrounded by a small collection of yellowish seeds at the base (Image: © Dr A. Martyn Ainsworth)
Threats & Conservation
Bird’s-eye primrose smut is of conservation concern in the UK. It was Red-Listed (unofficially) as Extinct in Great Britain in 2006 and added to the UK Biodiversity Action Plan (BAP) during the 2007 BAP review. It is currently recognised as a species of ‘principal importance for the conservation of biological diversity’ in England, and thereby listed in accordance with Section 41 of the Natural Environment and Rural Communities Act 2006. Following its rediscovery in England in 2010, it now occupies a single known site (so would qualify for Critically Endangered status) but further field survey work is required to provide a clearer picture of its current British distribution. Conservation of this fungus is dependent on that of its host plant (assessed as Vulnerable) and its habitat. Further work is required to investigate how many and which primrose populations currently host the extant smut and how the numbers of smutted flowers/plants might vary naturally from year to year.
Re-discovery of 'extinct' fungus
Bird’s-eye primrose smut was rediscovered on six scattered plants after two hours of ovary-squeezing in wet, lime-rich moorland. Kew mycologist Dr A. Martyn Ainsworth (who is part-funded by Natural England) was stopping over in a nearby village on a journey to Scotland and decided to visit a site where he had seen bird’s-eye primrose in flower several years ago.
Bird's-eye primrose smut at Kew
Bird’s-eye primrose smut has not been recorded in the Gardens at Kew. However there are dried collections of this species from throughout its range preserved in the Kew Mycology Herbarium (Fungarium), which are made available to bona fide researchers by appointment.
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