The Local Flora and Rare Native Plant Collection is a high profile habitat and phytogeographic display developed in response to the ‘Global Strategy for Plant for Conservation’, which delivers a number of ‘target’ objectives including, growing and interpreting rare and threatened native plant species in ‘ex-situ’ conservation collections. Botanic Gardens are at the fore front of this conservation and interpretation work.
The Collection is represented by, The Avon Gorge Display; The Deciduous Woodland Display; The Mendip Hills, Limestone Cliffs and Coastal Islands Display; The Aquatic Plants Display and The Local Calcareous Grassland Display.
The Avon Gorge is a 1.5 mile (2.5km) long gorge cut by the river Avon through a ridge of predominantly Carboniferous limestone. The mainly south to west aspect and south easterly dip of the strata provide a sheltered microclimate of sun-baked niches suitable for plants at the northern end of their natural range such as: round-headed leek Allium sphaerocephalon and Bristol rock-cress Arabis scabra. Forming part of ancient scrub and grassland communities found growing on carboniferous limestone, plants such as; western spiked speedwell Veronica spicata subsp. hybrida, dwarf sedge Carex humilis, fingered sedge Carex digitata, hutchinsia Hornungia petraea, autumn squill Scilla autumnalis, rock stonecrop, Sedum fosterianum and pale St. John’s-wort Hypericum montanum are some of the rare or nationally scarce plants found in this biodiverse environment. Many are threatened in the wild by encroaching scrub, introduced species and engineering works. Honewort Trinia glauca has suffered particularly badly from habitat loss due to scrub encroachment. Seed collected from one of the last remaining populations has been grown at the garden and is displayed with the objective of establishing a viable ex-situ population. Two rare endemic whitebeams, Sorbus bristoliensis and Sorbus wilmottiana are grown. A number of other endemic whitebeams have recently been discovered and described and are currently been propagated for eventual planting in this display.
Deciduous woodland over limestone is common in the Bristol region. This display forms part of the western side of the Avon Gorge and is known locally as Leigh Woods, recognised as an ancient woodland site with populations of small-leaved lime Tilia cordata and wild service-tree Sorbus torminalis. Forming part of the Avon Gorge display, but displaying predominantly woodland and shade loving species the rocky outcrop has been planted with smaller growing trees and herbaceous plants. Sorbus porrigentiformis grows horizontally out from the rock illustrating its adaptation to growing in rock ledges and on cliff faces, while Sorbus eminens and Sorbus anglica both endemic to the west of Britain are displayed. Lily-of-the-valley Convallaria majalis, angular solomon’s seal Polygonatum odoratum, spurge-laurel Daphne laureola and southern polypody Polypodium cambricum represent smaller growing species.
Limestone woodland species from other local sites are also represented such as limestone fern Gymonocarpum robertianum.
Hedgerow and woodland habitats are incorporated into the existing ancient woodland that is already present in the garden. This small fragment of ancient woodland of a once much larger deer parkland dates back to Elizabethan times. Further development of this display will see the planting of wild service-tree Sorbus torminalis and the endangered limestone woundwort Stachys alpina as part of woodland edge display.
The Mendip Hills display illustrates the scrubland and grassland flora found on Carboniferous limestone. Cheddar pink Dianthus gratianopolitanus has its only UK population amongst the rocky outcrops of Cheddar Gorge. While purple gromwell Lithospermum purpureocaeruleum is found frequently in Mendip woods. The starved sedge Carex depauperata is grown and thrives in a base rich soil amongst the limestone rocks. Locally it grows at only one location in woods and a hedge bank near to Axbridge, one of only two UK sites. White rockrose Helianthemum appenninum is found growing at the western extreme of the Mendip Hills, one of only two UK sites. In May its papery white flowers dominate the display and can be seen growing in dry thin soil, its favoured environment.
The limestone cliffs and coastal islands display is comprised of Carboniferous limestone with an adjoining area of coastal sand. Wild leek Alllium ampeloprasum var. ampeloprasum is classed as an archaeophyte and found locally growing on the limestone island of Steep Holm in the Bristol Channel, while Babington’s leek Allium ampeloprasum var. babingtonii is found growing on coastal cliffs and dunes of Cornwall. Both are displayed next to each other allowing visitors to make comparisons between these two related varieties. Sea stock Matthiola sinuata, a species found in dune slacks in North Devon and South Wales, and shore dock Rumex rupestris, a coastal species from south Devon and Cornwall are displayed. Both plants are threatened in the wild with populations declining due to habitat change and loss.
The Bristol area has an abundance of ditches, drainage rhynes and river systems. Aquatic communities are displayed in the large pool containing plantings of bogbean Menyanthes trifoliata and water plantain Alisma plantago-aquatica. Further development of the aquatic plantings is planned and will include water lily Nymphaea alba, yellow water-lily Nuphar lutea and frogbit Hydrocharis morsus-ranae.
Local calcareous grassland habitats of Durdham and Clifton Downs are represented. This display showcases the herb rich grassland overlying the thin soils of these biologically rich areas. Species grown include: crested dogs tail Cynosurus cristatus and compact brome Anisantha madritensis into which herb plants will be planted including cowlsip Primula veris, horseshore vetch Hippocrepis comosa, kidney vetch Anthyllis vulneraria, and common centaury Centaurium erythraea. The removal of nutrient rich top soil and the importation of nutrient poor soil and aggregate mix from local quarries has helped to create a low nutrient environment, important to prevent strong growing grasses from dominating the display. The hemi-parasite yellow rattle Rhinanthus minor has been sown and will reduce the vigour of grass species further so allowing the herb flora to proliferate.
The display features a mown path allowing visitors to enjoy the diversity of grasses and herb plants. The addition of terrestrial orchid species will begin when the grass sward is established. Common spotted Dactylorhiza fuchsii already grows nearby and will doubtless seed itself into the display. Bee orchid Ophrys apifera and autumn lady’s tresses Spiranthes spiralis will be introduced at a later date.
Recently described whitebeamsfrom the Avon Gorge; Sorbus leighensis, Sorbus whiteana, Sorbus x avonensis, Sorbus x robertsonii and Sorbus x houstoniae are currently being raised in the garden for planting along one side of the calcareous grassland display.
A seasonal pool puddled with clay will be created to grow the local endemic Badgeworth buttercup, Ranunculus ophioglossifolius. This obscure local plant only grows in a seasonal pool at Badgeworth in Gloucestershire. Cattle entering the pool to drink poach the soft earth with their hooves bringing dormant seeds to the surface. This specific environment will be reproduced each autumn.