Bwrdd Arthur

Site of Special Scientific Interest · 53.3108, -4.1239

Geology & landscape

Geological Period: Carboniferous · Rock Type: Carboniferous Limestone, Limestone

Description

Description Bwrdd Arthur, a small flat-topped Carboniferous Limestone hill reaching an altitude of 160m, is designated for its botanical interest. It is one of the larger and more diverse limestone sites in West Gwynedd. A number of plant communities are represented including limestone grassland, calcareous heath characterised by the presence of heather Calluna vulgaris, bell heather Erica cinerea and western gorse Ulex gallii and scrub with stands of common gorse Ulex europaeus, elder Sambucus nigra, hawthorn Crataegus monogyna, blackthorn Prunus spinosa and bramble Rubus. The limestone grassland includes characteristic species such as common rockrose Helianthemum nummularium, pale St. John's-wort Hypericum montanum, long-stalked crane's-bill Geranium columbinum and and meadow oat grass Avenula pratensis. The limestone exposures support the nationally rare species, hoary rockrose Helianthemum oelandicum and ivy broomrape Orobanche hederae, whilst a number of uncommon bryophyte species occur on its south-facing slopes including Bryum canariense, B.elegans and Plasteurhynchium striatulum.

Species mentioned

English name
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Latin name
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IUCN / Red List Type Family
meadow oat grass Avenula pratensis Not listed in GB list grass poaceae
long stalked cranesbill Geranium columbinum VU herb geraniaceae
rock roses Helianthemum nummularium VU herb cistaceae
mountain St John's wort Hypericum montanum VU herb hypericaceae
ivy broomrape Orobanche hederae LC herb orobanchaceae
thread moss Bryum canariense LC moss bryales
Plasteurhynchium striatulum LC moss brachytheciaceae
hawthorn Crataegus monogyna LC shrub rosaceae
blackthorn Prunus spinosa LC shrub rosaceae
elder Sambucus nigra LC shrub caprifoliaceae
gorse Ulex europaeus LC shrub leguminosae
western gorse Ulex gallii LC shrub leguminosae
bell heather or ling Calluna vulgaris NT shrub dwarf ericaceae
bell heather Erica cinerea NT shrub dwarf ericaceae

Insects to look out for

These moths, butterflies and beetles are known to feed on plants recorded at this site, and carry a notable UK conservation status — but a host-plant being present doesn't mean the insect has actually been recorded here. Treat this as "worth watching for," not a confirmed sighting.

SpeciesStatusVia host-plant
Figure of eight
Diloba caeruleocephala
Endangered Crataegus spp., Prunus spinosa, Prunus spp.
The lappet
Gastropacha quercifolia
Endangered Crataegus monogyna, Prunus spinosa, Prunus spp.
Shoulder-striped clover
Heliothis maritima
Endangered Calluna vulgaris, Erica cinerea
Scarce vapourer
Orgyia recens
Endangered Crataegus spp., Prunus spinosa
Black hairstreak
Satyrium pruni
Endangered Prunus spinosa
Mouse moth
Amphipyra tragopoginis
Vulnerable Crataegus spp.
Northern brown
Aricia artaxerxes
Vulnerable Helianthemum nummularium
The sprawler
Asteroscopus sphinx
Vulnerable Crataegus spp., Prunus spinosa, Prunus spp.
Broom moth
Ceramica pisi
Vulnerable Calluna vulgaris
Mottled umber
Erannis defoliaria
Vulnerable Crataegus spp., Prunus spinosa
Satyr pug
Eupithecia satyrata
Vulnerable Calluna vulgaris, Helianthemum nummularium, Hypericum spp.
True lover's knot
Lycophotia porphyrea
Vulnerable Calluna vulgaris, Erica cinerea
The lackey
Malacosoma neustria
Vulnerable Crataegus monogyna, Prunus spinosa, Prunus spp.
Pale brindled
Phigalia pilosaria
Vulnerable Crataegus monogyna, Prunus spinosa
Silver studded blue
Plebejus argus
Vulnerable Calluna vulgaris, Erica cinerea, Helianthemum nummularium, Ulex spp.
Lead belle
Scotopteryx mucronata
Vulnerable Ulex europaeus
Brown hairstreak
Thecla betulae
Vulnerable Prunus spinosa
Early moth
Theria primaria
Vulnerable Crataegus monogyna, Prunus spinosa
Pale eggar
Trichiura crataegi
Vulnerable Calluna vulgaris, Crataegus monogyna, Erica cinerea, Prunus spinosa
Flounced chestnut
Agrochola helvola
Near Threatened Calluna vulgaris, Crataegus monogyna
Beaded chestnut
Agrochola lychnidis
Near Threatened Crataegus monogyna
Grey chi
Antitype chi
Near Threatened Crataegus monogyna
Garden tiger
Arctia caja
Near Threatened Prunus spinosa
Grey scalloped
Dyscia fagaria
Near Threatened Calluna vulgaris, Erica cinerea
Large thorn
Ennomos autumnaria
Near Threatened Crataegus spp., Prunus spinosa, Prunus spp.
Autumnal rustic
Eugnorisma glareosa
Near Threatened Calluna vulgaris, Erica cinerea
Grey pug
Eupithecia subfuscata
Near Threatened Crataegus monogyna, Prunus spinosa
White-spotted pug
Eupithecia tripunctaria
Near Threatened Sambucus nigra
Double dart
Graphiphora augur
Near Threatened Crataegus spp., Prunus spinosa
Weaver's wave
Idaea contiguaria
Near Threatened Calluna vulgaris
Silky wave
Idaea dilutaria
Near Threatened Helianthemum nummularium

Host-plant data: Cook et al. (2025), Traits data for the butterflies and macro-moths of Great Britain and Ireland, 2024, UK Centre for Ecology & Hydrology / Butterfly Conservation; and Padovani et al. (2020), Database of Insects and their Food Plants (DBIF), UK Centre for Ecology & Hydrology (both Open Government Licence). Contains data supplied by UK Centre for Ecology & Hydrology.

Plant communities

W21 — Hedgerow scrub, Mixed scrub

Crataegus monogyna-Hedera helix scrub

Matches 3 species from the description above: Crataegus monogyna, Prunus spinosa, Sambucus nigra

Hedera helix, Salix cinerea, Acer pseudoplatanus, Ilex aquifolium, Betula pendula, Corylus avellana, Fagus sylvatica, Quercus robur, Fraxinus excelsior, Malus sylvestris, Sorbus aria, Taxus baccata, Ulmus glabra, Ulmus procera, Sambucus nigra, Viburnum lantana, Euonymus europaeus, Cornus sanguinea, Juniperus communis, Ligustrum vulgare, Clematis vitalba, Rhamnus cathartica, Crataegus laevigata, Crataegus monogyna, Prunus spinosa, Juncus effusus, Plagiomnium undulatum, Brachythecium rutabulum, Kindbergia praelonga, Rhynchostegium confertum, Tamus communis, Heracleum sphondylium, Torilis japonica, Arum maculatum, Arctium minus, Cirsium arvense, Lonicera periclymenum, Moehringia trinervia, Silene dioica, Stellaria graminea, Stellaria holostea, Stellaria media agg., Calystegia sepium, Mercurialis perennis, Geranium robertianum, Iris foetidissima, Glechoma hederacea, Lamium purpureum, Origanum vulgare, Stachys sylvatica, Teucrium scorodonia, Allium ursinum, Hyacinthoides non-scripta, Circaea lutetiana, Rumex sanguineus, Anemone nemorosa, Ranunculus repens, Fragaria vesca, Geum urbanum, Potentilla sterilis, Poterium sanguisorba, Rosa arvensis, Rosa canina, Rubia peregrina, Rubus fruticosus agg., Galium aparine, Urtica dioica, Viola riviniana, Anisantha sterilis, Arrhenatherum elatius, Brachypodium pinnatum, Brachypodium sylvaticum, Bromopsis erecta, Dactylis glomerata, Elytrigia repens, Holcus lanatus, Holcus mollis, Poa trivialis, Asplenium scolopendrium, Pteridium aquilinum, Dryopteris filix-mas

W22 — Hedgerow scrub, Mixed scrub

Prunus spinosa-Rubus fruticosus scrub

Matches 2 species from the description above: Prunus spinosa, Ulex europaeus

Hedera helix, Acer campestre, Corylus avellana, Ulex europaeus, Prunus spinosa, Plagiomnium undulatum, Brachythecium rutabulum, Eurhynchium striatum, Kindbergia praelonga, Thuidium tamariscinum, Atrichum undulatum, Lophocolea bidentata, Achillea millefolium, Cardamine flexuosa, Lonicera periclymenum, Moehringia trinervia, Silene dioica, Silene uniflora, Stellaria media agg., Mercurialis perennis, Geranium robertianum, Stachys sylvatica, Teucrium scorodonia, Hyacinthoides non-scripta, Oxalis acetosella, Digitalis purpurea, Plantago lanceolata, Veronica chamaedrys, Armeria maritima, Rumex acetosa, Filipendula ulmaria, Geum urbanum, Rosa canina, Rubus fruticosus agg., Rubus idaeus, Galium aparine, Urtica dioica, Viola riviniana, Agrostis capillaris, Brachypodium sylvaticum, Dactylis glomerata, Festuca rubra, Holcus lanatus, Holcus mollis, Poa trivialis, Asplenium scolopendrium, Pteridium aquilinum, Dryopteris borreri, Dryopteris filix-mas

W20 — Montane scrub

Salix lapponum-Luzula sylvatica scrub

Matches 1 species from the description above: Calluna vulgaris

Salix arbuscula, Salix cinerea, Salix lapponum, Salix myrsinites, Salix phylicifolia, Salix reticulata, Empetrum nigrum, Calluna vulgaris, Salix lanata, Vaccinium myrtillus, Vaccinium uliginosum, Carex atrata, Carex bigelowii, Carex binervis, Carex flacca, Luzula multiflora, Luzula sylvatica, Huperzia selago, Selaginella selaginoides, Aulacomnium palustre, Mnium hornum, Philonotis fontana, Plagiomnium undulatum, Rhizomnium punctatum, Dicranum bonjeanii, Dicranum majus, Dicranum scoparium, Fissidens adianthoides, Racomitrium lanuginosum, Calliergonell cuspidatum, Ctenidium molluscum, Hylocomium splendens, Hypnum callichroum, Hypnum cupressiforme, Palustriella commutatum, Plagiothecium denticulatum, Plagiothecium undulatum, Pleurozium schreberi, Ptilium crista-castrensis, Rhytidiadelphus loreus, Rhytidiadelphus squarrosus, Rhytidiadelphus triquetrus, Sanionia uncinata, Scorpidium revolvens, Thuidium tamariscinum, Atrichum undulatum, Polytrichastrum alpinum, Sphagnum capillifolium, Sphagnum fallax, Sphagnum girgensohnii, Sphagnum palustre, Sphagnum russowii, Sphagnum squarrosum, Sphagnum subnitens, Sphagnum teres, Barbilophozia barbata, Chiloscyphus polyanthos, Diplophyllum albicans, Lophocolea bidentata, Plagiochila porelloides, Ptilidium ciliare, Scapania undulata, Cladonia squamosa, Peltigera canina, Angelica sylvestris, Caltha palustris, Hieraclium spp., Saussurea alpina, Solidago virgaurea, Campanula rotundifolia, Succisa pratensis, Valeriana officinalis, Rhodiola rosea, Vaccinium vitis-idaea, Thymus praecox, Epilobium anagallidifolium, Dactylorhiza viridis, Euphrasia officinalis, Rhinanthus minor, Oxalis acetosella, Oxyria digyna, Polygonum viviparum, Rumex acetosa, Anemone nemorosa, Ranunculus acris, Thalictrum alpinum, Alchemilla alpina, Alchemilla glabra, Filipendula ulmaria, Geum rivale, Galium boreale, Galium saxatile, Saxifraga aizoides, Saxifraga hypnoides, Saxifraga oppositifolia, Saxifraga stellaris, Viola riviniana, Agrostis canina, Agrostis capillaris, Anthoxanthum odoratum, Deschampsia cespitosa, Deschampsia flexuosa, Festuca ovina, Festuca rubra, Nardus stricta, Dryopteris dilatata, Phegopteris connectilis