Banc Hirllwyn

Site of Special Scientific Interest · 52.1886, -3.3119

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Powys County

Geology & landscape

Geological Period: Ordovician

Landscape processes: Volcanic / Igneous

Description

Description Banc Hirllwyn is of special interest for its areas of acid grassland vegetation and the nationally scarce maiden pink Dianthus deltoides. The site is situated 1km to the north-west of the village of Hundred House at an altitude of 300 m. It occupies a prominent ridge of volcanic rocks which forms part of the Llandrindod Wells Ordovician inlier. Shallow soils over rock outcrops support stands of acid grassland along the south and south-east facing slopes of the bank. The grassland is prone to drought during the summer months, and has a high proportion of annual plants adapted to survive such conditions. The main grasses in the short, open sward are sheep’s fescue Festuca ovina, common bent Agrostis capillaris, early hair-grass Aira praecox and squirrel-tail fescue Vulpia bromoides. Common associates include sheep’s sorrel Rumex acetosella, common mouse-ear Cerastium fontanum, parsley piert Aphanes arvensis, wall speedwell Veronica arvensis, common bird’s-foot-trefoil Lotus corniculatus, lady’s bedstraw Galium verum, spring sedge Carex caryophyllea, the uncommon upright chickweed Moenchia erecta, wild thyme Thymus polytrichus, the mosses Dicranum scoparium, Brachythecium albicans and Hypnum cupressiforme and the lichens Peltigera rufescens and Cladonia spp.. Other locally frequent components of the vegetation include dove’s-foot cranesbill Geranium molle, yarrow Achillea millefolium, harebell Campanula rotundifolia, tormentil Potentilla erecta, carline thistle Carlina vulgaris and the nationally scarce maiden pink and lichen Peltigera canina. The locally scarce annual knawel Scleranthus annuus has also been recorded at the site. Small rock outcrops within the site support mosses, such as Hedwigia sp. and a variety of lichens, including Rhizocarpon viridiatrum, Porpidia cinereoatra and the locally uncommon Caloplaca arenaria, Caloplaca ceracea and Porpidia platycarpoides. The lower flanks of the bank support open oak Quercus spp. woodland, which provides additional interest. The acid grassland extends under the tree canopy in places and intergrades with species-poor neutral grassland on the deeper soils of the plateau top. This area has been subject to past agricultural improvement but is now reverting to a more natural state.

Species mentioned

English name
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Latin name
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IUCN / Red List Type Family
common bent Agrostis capillaris LC grass poaceae
early hair grass Aira praecox VU grass poaceae
parsley piert Aphanes arvensis LC grass rosaceae
sheep's fescue Festuca ovina LC grass poaceae
squirrel tail fescue Vulpia bromoides LC grass poaceae
yarrow Achillea millefolium LC herb asteraceae
harebell Campanula rotundifolia LC herb campanulaceae
carline thistle Carlina vulgaris LC herb asteraceae
common mouse ear Cerastium fontanum LC herb carophyllaceae
maiden pink Dianthus deltoides NT herb carophyllaceae
lady's bedstraw Galium verum LC herb rubiaceae
dove's foot cranesbill Geranium molle LC herb geraniaceae
birdsfoot trefoil Lotus corniculatus LC herb fabaceae
upright chickweed Moenchia erecta VU herb carophyllaceae
tormentil Potentilla erecta LC herb rosaceae
sheep's sorrel Rumex acetosella NT herb polygonaceae
annual knawel Scleranthus annuus DD herb carophyllaceae
wild thyme Thymus polytrichus Not listed in GB list herb lamiaceae
wall speedwell Veronica arvensis LC herb plantaginaceae
granite firedot lichen Caloplaca arenaria Not listed in GB list lichen no common name
gray-rimmed firedot lichen Caloplaca ceracea Not listed in GB list lichen no common name
dog-lichen Peltigera canina LC lichen no common name
field dog-lichen Peltigera rufescens LC lichen no common name
map lichens Rhizocarpon Not listed in GB list lichen rhizocarpaceae
whitish feather moss Brachythecium albicans LC moss hypnales
broom fork moss Dicranum scoparium LC moss dicranales
Cyprus leaved plait moss Hypnum cupressiforme LC moss hypnales
spring-sedge Carex caryophyllea NT sedge cyperaceae

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
Black-veined moth
Siona lineata
Critically Endangered Lotus corniculatus
New forest
Zygaena viciae
Critically Endangered Lotus corniculatus
Straw belle
Aspitates gilvaria
Endangered Achillea millefolium, Lotus corniculatus
Wood white
Leptidea sinapis
Endangered Lotus corniculatus
Heath fritillary
Melitaea athalia
Endangered Achillea millefolium
Fiery clearwing
Pyropteron chrysidiformis
Endangered Rumex acetosella
Slender scotch
Zygaena loti
Endangered Lotus corniculatus
Mouse moth
Amphipyra tragopoginis
Vulnerable Lotus corniculatus
Broom moth
Ceramica pisi
Vulnerable Rumex spp.
Dingy skipper
Erynnis tages
Vulnerable Lotus corniculatus
Satyr pug
Eupithecia satyrata
Vulnerable Galium spp.
Garden dart
Euxoa nigricans
Vulnerable Rumex spp.
White-line dart
Euxoa tritici
Vulnerable Cerastium spp., Galium verum
Grayling
Hipparchia semele
Vulnerable Aira praecox, Festuca ovina
Bedstraw hawk-moth
Hyles gallii
Vulnerable Galium spp.
Silver studded blue
Plebejus argus
Vulnerable Lotus corniculatus
Grizzled skipper
Pyrgus malvae
Vulnerable Potentilla erecta
Beaded chestnut
Agrochola lychnidis
Near Threatened Rumex spp.
Grey chi
Antitype chi
Near Threatened Rumex spp.
Garden tiger
Arctia caja
Near Threatened Rumex spp.
No common name
Chrysolina marginata
Near Threatened Achillea millefolium
The sallow
Cirrhia icteritia
Near Threatened Rumex spp.
Small heath
Coenonympha pamphilus
Near Threatened Agrostis spp., Festuca spp.
Autumnal rustic
Eugnorisma glareosa
Near Threatened Festuca ovina, Galium spp., Rumex spp.
Tawny speckled
Eupithecia icterata
Near Threatened Achillea millefolium
Grey pug
Eupithecia subfuscata
Near Threatened Achillea millefolium
Bordered pug
Eupithecia succenturiata
Near Threatened Achillea millefolium
Silver-spotted skipper
Hesperia comma
Near Threatened Festuca ovina
Wall
Lasiommata megera
Near Threatened Agrostis spp.
Rosy minor
Litoligia literosa
Near Threatened Festuca ovina
Dark-barred twin-spot carpet
Xanthorhoe ferrugata
Near Threatened Galium spp., Rumex spp.

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

U4 — Lowland dry acid grassland, Upland acid grassland, Upland calcareous grassland

Festuca ovina-Agrostis capillaris-Galium saxatile grassland

Matches 11 species from the description above: Achillea millefolium, Agrostis capillaris, Campanula rotundifolia, Carex caryophyllea, Cerastium fontanum, Dicranum scoparium, Festuca ovina, Galium verum, Hypnum cupressiforme, Lotus corniculatus, Potentilla erecta

Calluna vulgaris, Vaccinium myrtillus, Carex binervis, Carex caryophyllea, Carex echinata, Carex nigra, Carex panicea, Carex pilulifera, Juncus effusus, Juncus squarrosus, Luzula campestris, Luzula multiflora, Luzula sylvatica, Mnium hornum, Dicranum scoparium, Racomitrium lanuginosum, Hylocomium splendens, Hypnum cupressiforme, Pleurozium schreberi, Pseudoscleropodium purum, Rhytidiadelphus loreus, Rhytidiadelphus squarrosus, Rhytidiadelphus triquetrus, Thuidium tamariscinum, Polytrichastrum alpinum, Polytrichum commune, Lophocolea bidentata, Conopodium majus, Achillea millefolium, Bellis perennis, Cirsium arvense, Cirsium vulgare, Taraxacum officianalis, Campanula rotundifolia, Succisa pratensis, Cerastium fontanum, Lathyrus montanus, Lotus corniculatus, Trifolium pratense, Trifolium repens, Thymus praecox, Euphrasia officinalis, Oxalis acetosella, Plantago lanceolata, Veronica chamaedrys, Veronica officinalis, Polygala serpyllifolia, Rumex acetosa, Primula vulgaris, Anemone nemorosa, Ranunculus acris, Ranunculus repens, Potentilla erecta, Poterium sanguisorba, Galium saxatile, Galium verum, Viola lutea, Viola palustris, Viola riviniana, Agrostis canina, Agrostis capillaris, Alopecurus pratensis, Anthoxanthum odoratum, Avenula pratensis, Briza media, Cynosurus cristatus, Dactylis glomerata, Danthonia decumbens, Deschampsia cespitosa, Deschampsia flexuosa, Festuca ovina, Festuca rubra, Holcus lanatus, Holcus mollis, Lolium perenne, Molinia caerulea, Nardus stricta, Poa annua, Poa pratensis, Blechnum spicant, Pteridium aquilinum, Chara curta

U5 — Upland acid grassland, Upland calcareous grassland

Nardus stricta-Galium saxatile grassland

Matches 7 species from the description above: Agrostis capillaris, Campanula rotundifolia, Cerastium fontanum, Dicranum scoparium, Festuca ovina, Hypnum cupressiforme, Potentilla erecta

Empetrum nigrum subsp.nigrum, Calluna vulgaris, Erica cinerea, Erica tetralix, Vaccinium myrtillus, Carex bigelowii, Carex binervis, Carex demissa, Carex nigra, Carex panicea, Carex pilulifera, Carex pulicaris, Eriophorum angustifolium, Eriophorum vaginatum, Trichophorum cespitosum, Juncus effusus, Juncus squarrosus, Luzula campestris, Luzula multiflora, Luzula sylvatica, Huperzia selago, Selaginella selaginoides, Aulacomnium palustre, Pohlia nutans, Campylopus flexuosus, Dicranella heteromalla, Dicranum scoparium, Racomitrium lanuginosum, Calliergonell cuspidatum, Hylocomium splendens, Hypnum cupressiforme, Plagiothecium undulatum, Pleurozium schreberi, Pseudoscleropodium purum, Rhytidiadelphus loreus, Rhytidiadelphus squarrosus, Thuidium tamariscinum, Polytrichastrum alpinum, Polytrichum commune, Polytrichum formosum, Polytrichum juniperinum, Sphagnum papillosum, Barbilophozia floerkei, Calypogeia muelleriana, Diplophyllum albicans, Lophocolea bidentata, Lophozia ventricosa, Pleurozia purpurea, Ptilidium ciliare, Scapania gracilis, Cetraria islandica, Cladonia uncialis, Cirsium palustre, Scorzoneroides autumnalis, Campanula rotundifolia, Cerastium fontanum, Equisetum palustre, Vaccinium vitis-idaea, Trifolium repens, Narthecium ossifragum, Plantago lanceolata, Polygala serpyllifolia, Anemone nemorosa, Ranunculus acris, Alchemilla alpina, Potentilla erecta, Galium saxatile, Viola riviniana, Agrostis capillaris, Agrostis vinealis, Anthoxanthum odoratum, Danthonia decumbens, Deschampsia cespitosa, Deschampsia flexuosa, Festuca ovina, Festuca rubra, Molinia caerulea, Nardus stricta, Blechnum spicant

U2 — Brownfield, Lowland dry acid grassland, Upland acid grassland

Deschampsia flexuosa grassland

Matches 6 species from the description above: Agrostis capillaris, Dicranum scoparium, Festuca ovina, Hypnum cupressiforme, Potentilla erecta, Rumex acetosella

Betula pendula, Quercus hybrid, Empetrum nigrum subsp.nigrum, Calluna vulgaris, Vaccinium myrtillus, Ulex europaeus, Carex nigra, Eriophorum vaginatum, Juncus effusus, Juncus squarrosus, Luzula multiflora, Orthodontium lineare, Pohlia nutans, Campylopus pyriformis, Dicranum scoparium, Hypnum cupressiforme, Plagiothecium undulatum, Pleurozium schreberi, Rhytidiadelphus squarrosus, Polytrichum commune, Polytrichum piliferum, Barbilophozia floerkei, Cladonia gracilis, Chamerion angustifolium, Rumex acetosa, Rumex acetosella, Potentilla erecta, Rubus fruticosus agg., Galium saxatile, Agrostis capillaris, Agrostis vinealis, Anthoxanthum odoratum, Deschampsia flexuosa, Festuca ovina, Festuca rubra, Holcus mollis, Molinia caerulea, Nardus stricta, Poa annua, Pteridium aquilinum

U3 — Lowland dry acid grassland, Upland acid grassland

Agrostis curtisii grassland

Matches 5 species from the description above: Agrostis capillaris, Dicranum scoparium, Festuca ovina, Hypnum cupressiforme, Potentilla erecta

Calluna vulgaris, Erica cinerea, Erica tetralix, Vaccinium myrtillus, Ulex europaeus, Ulex gallii, Carex binervis, Carex panicea, Carex pilulifera, Luzula campestris, Dicranum scoparium, Hylocomium splendens, Hypnum cupressiforme, Pleurozium schreberi, Pseudoscleropodium purum, Rhytidiadelphus squarrosus, Cladonia floerkeana, Cladonia impexa, Hypochaeris radicata, Teucrium scorodonia, Polygala serpyllifolia, Potentilla erecta, Galium saxatile, Agrostis capillaris, Agrostis curtisii, Agrostis vinealis, Anthoxanthum odoratum, Danthonia decumbens, Deschampsia flexuosa, Festuca ovina, Festuca rubra, Molinia caerulea, Nardus stricta, Pteridium aquilinum

M25 — Blanket bog, Coastal floodplain grazing marsh, Lowland fen, Purple moor grass and rush pasture, Upland acid grassland

Molinia caerulea-Potentilla erecta mire

Matches 3 species from the description above: Agrostis capillaris, Festuca ovina, Potentilla erecta

Salix cinerea, Calluna vulgaris, Erica tetralix, Myrica gale, Vaccinium oxycoccos, Ulex europaeus, Ulex gallii, Carex echinata, Carex flacca, Carex nigra, Carex panicea, Eriophorum angustifolium, Schoenus nigricans, Juncus acutiflorus, Juncus articulatus, Juncus effusus, Juncus subnodulosus, Luzula campestris, Luzula multiflora, Aulacomnium palustre, Pohlia nutans, Calliergon giganteum, Calliergonell cuspidatum, Hypnum jutlandicum, Kindbergia praelonga, Pleurozium schreberi, Pseudoscleropodium purum, Rhytidiadelphus squarrosus, Polytrichum commune, Sphagnum auriculatum, Sphagnum capillifolium, Sphagnum fallax, Sphagnum palustre, Sphagnum papillosum, Sphagnum subnitens, Calypogeia fissa, Cephalozia bicuspidata, Lophocolea bidentata, Lophozia ventricosa, Angelica sylvestris, Carum verticillatum, Hydrocotyle vulgaris, Achillea ptarmica, Centaurea nigra, Cirsium palustre, Eupatorium cannabinum, Pulicaria dysenterica, Serratula tinctoria, Cardamine pratensis, Lobelia urens, Succisa pratensis, Valeriana officinalis, Equisetum palustre, Lotus pedunculatus, Hypericum pulchrum, Hypericum tetrapterum, Mentha aquatica, Scutellaria minor, Menyanthes trifoliata, Narthecium ossifragum, Epilobium palustre, Dactylorhiza maculata, Rumex acetosa, Ranunculus acris, Ranunculus flammula, Filipendula ulmaria, Potentilla erecta, Rubus fruticosus agg., Galium palustre, Viola palustris, Agrostis canina, Agrostis capillaris, Agrostis curtisii, Agrostis stolonifera, Anthoxanthum odoratum, Danthonia decumbens, Deschampsia cespitosa, Festuca ovina, Festuca rubra, Holcus lanatus, Molinia caerulea, Nardus stricta, Phragmites australis, Dryopteris carthusiana, Osmunda regalis