First of all, I must recommend the following website, which I have used extensively for identifying many difficult plants - www.naturespot.org.uk.
(All photos taken at OPS.)
Total number of species (all genuses) reported at OPS = 1122 (362 Plants, 369 Insects, 137 Animals/Fish, 253 Birds (inc. escapes)).
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Annual Mercury, BRERC record 31/12/86.
Beaked Hawk's-beard, BRERC record 4/5/07.
Bittersweet (aka Woody Nightshade)
Black Bindweed, BRERC record 4/5/07.
Branched Bur-reed, BRERC record 2/7/02.
Bristly Oxtongue, BRERC record 16/6/16.
Buck's-horn Plantain, BRERC record 2/10/08.
Bulbous Foxtail - identified in WWT survey within 1km (nationally scarce)
Bush Vetch, BRERC record 2/7/2002.
Canadian Fleabane by jetty. Tiny white/yellow flowers
Chicory in the wildflower meadow next to car park
Charlock, BRERC record 4/5/2007.
Coltsfoot large leaves, where weather tower used to be
Common Broomrape. A parasite of clover.
Common Dog-violet (white version in wood by orchard)
Common Eyebright very pretty small plant, on path of Lagoon 3, at SW end.
Common Figwort, BRERC record 17/7/2011.
Common Hemp-nettle, BRERC record 31/12/1986.
Common Ragwort common yellow plant around the lagoons
Common Spotted Orchid - lip divided into three equal lobes and marked with dark pink dashes and broken lines. (Leaves - not shown - spotted.)
Corn Parsley, BRERC record 2/7/2002.
Dog Violet (inc. white-flowered)
Dove's-foot Crane's-bill, BRERC record 31/12/1986.
Dyer's Greenweed, BRERC record 31/12/1986.
Early Marsh Orchid
Giant Hogweed not on site currently
Goldilock's Buttercup in woods
Grape Hyacinth garden escape on seawall at Shepperdine
Greater Bird's-foot Trefoil, BRERC record 16/6/2016.
Greater Knapweed paints the meadow next to the car park purple in late summer !
Greater Sea-spurrey, BRERC record 31/12/1998.
Gypsywort bank of lake, next to road (where dogs go in lake). Like mint, but with no smell.
Hairy Tare, BRERC record 16/6/2016.
Hemlock, BRERC record 17/7/2011.
Hemp Agrimony Large patches on Lagoon 2
Hoary Willowherb - WWT survey, Lagoon 3, 2019
Honeysuckle, BRERC record 13/12/2006.
Ladys Bedstraw common on the path round Lagoon 3
Lesser Hawkbit, BRERC record 16/6/2016.
Lesser Stitchwort, BRERC record 2/7/2002.
Lesser Trefoil, BRERC record 16/6/2016.
Many-seeded Goosefoot, BRERC record 31/12/1986.
Meadow Thistle very common (note smooth stems)
Musk Mallow, usally pink flowers but also this white form.
Opium Poppy garden escape, Lagoon 2
Perennial Sow-thistle on the saltmarsh by the jetty, late summer
Pale Persicaria, BRERC record 31/12/1986.
Perforate St John's-wort along tarmacd path to Lagoon 2
Petty Spurge, BRERC record 17/7/2011.
Procumbent Pearlwort, BRERC record 17/7/2011.
Red Bartsia low-lying but distinctive, along the paths round Lagoon 2
Ribbed Melilot, BRERC record 2/10/2008.
Round-leaved Crane's-bill, BRERC record 17/7/2011.
Sand Crocus - on stony area of Lagoon 2, near pond.
Scented Mayweed (has hollow center to flowers), BRERC record 31/12/1986.
Scentless Mayweed Lagoon 3, by the stone pile
Sea Clover - identified in WWT survey within 1km (nationally scarce). At top of the seawall, by Lagoons 1/2.
Sea Radish - along shore, especially by the jetty
Shepperd's-purse, BRERC record 31/12/1986.
Silverweed, BRERC record 16/6/2016.
Smooth Cats Ear
Smooth Sow-thistle, BRERC record 4/5/2007.
Southern Marsh Orchid - rounded side lobes and a small toothlike central lobe; marked with darker dots and dashes. (Leaves - not shown - usually unspotted.)
Spear-leaved Orache - along shore, especially by the jetty
Babington's Orache - BRERC record, 31/12/98
Spotted Medick black spots in the centre of clover-like leaves. On Lagoon paths.
Square-stalked St John's-wort, BRERC record 2/7/2002.
Square-stalked Willowherb, BRERC record 16/6/2016.
Sticky Mouse-ear, BRERC record 16/6/2016.
Stone Parsley, BRERC record 17/7/2011.
Strawberry Clover, BRERC record 31/12/1998.
Sun Spurge around the jetty fence
Sweet Violet (white form) near orchard.
Swine-cress, BRERC record 31/12/1986.
Tall Melilot common on path of Lagoon 2
Travellers Joy (aka Old Mans Beard)
Thrift (or Sea Pink) a few clumps on the sea-wall by Lagoon 2
Thyme-leaved Speedwell, BRERC record 17/7/2011.
Upright Hedge Parsley
Wall Speedwell, BRERC record 16/6/2016.
Water Mint Lagoon 2
Wild Carrot the white flowerheads have a single purple flower in the middle (cultivated carrots belong to a different subspecies).
Wild Parsnip - Lagoon 2
Zigzag Clover, BRERC record 31/12/1986.
Bogbean - in shallow pond by visitor centre
Bulrush, BRERC record, in ponds, 13/11/2017
Common Duckweed, BRERC record, in ponds, 2/7/2002
Fools Watercress in the rhines (or on the banks after the farmers dredging !)
Lesser Water-parsnip, BRERC record 2/7/2002.
Hemlock Water-dropwort - the UK's most deadly plant ! BRERC record, 16/6/2016
Lesser Reedmace/Lesser Bulrush - in shallow pond by visitor centre
Spiked Water Milfoil
New Zealand Pigmyweed - invasive that takes over ponds, and unfortunately is creating a large mat in the pond by Lagoon 2
Jointed Rush, BRERC record 17/7/2011.
Toad Rush, BRERC record 4/5/2007.
Aspen shimmers in wind. Tall specimens along main rhine, by entrance. Round, toothed leaves.
Austrian Pine, BRERC record 17/7/2011.
Black Hawthorn Two trees in hedge between shore and Lagoon 3.
Black Poplar quite large, heart-shaped leaves. Tall, thin trees.
Common Whitebeam - identified in WWT survey, 2019.
Cotoneaster (C. franchetti), Franchet's Cotoneaster. Single plant at north end of Lagoon 2 (red-orange berries in Sept). Non-native, garden escape, spread by birds eating the berries. (Note that many Cotoneaster, e.g. C. horizontalis, but NOT this one, cause problems to native plants by spreading and are illegal to plant in wild (i.e. added to Sched 9 of Wildlife & Countryside Act in 2010).)
Crack Willow the hedge across Lagoon 1 shows Crack Willow (yellowy branches, green leaves, on left) and White Willow (green branches, darker green and longer leaves with white backs, on right)
Damson (also Bullace recorded in BRERC, 2/7/02)
Eared Willow - identified in WWT survey, 2019.
Elm a good specimen is along the bridleway at far end of lake, which runs along the SW side of Lagoon 3. On left of path (over ditch), the first tree in the tall hedge just before path zig-zags.
Field Maple distinguished from Sycamore by sides of fruit being in a straight line. Large example on far side of main rhine, just down from entrance.
Grey Willow - identified in WWT survey, 2019.
Hornbeam - 4 specimens in hedge that runs from road along SW side of Lagoon 3.
Horse Chestnut - just one small tree growing through brambles on Lagoon 2.
Oak (Pendunculate Oak)
Osier (Willow) - identified in WWT survey, 2019.
Scots Pine all the pine trees on-site are this species.
Sea Buckthorn the large silvery bush on the seawall of Lagoon 1
Sloe (aka Blackthorn) white flowers before leaves appear, early Spring
Small-leaved Elm, BRERC record 17/7/2011.
Spindle pink fruit in late autumn. Specimen along tarmacd path to Lagoon 2, near old visitor centre
Sweet Chestnut the only specimen is on the lawn in front of the Gatehouse/old Visitor Centre
Turkey Oak nice specimen on right of approach road. Acorns have hairy base.
Wayfaring Tree shrub with red and black berries, Lagoon 2
White Poplar large specimen at SW end of Lagoon 3. White back to grey leaves.
White Willow see photo under Crack Willow, above.
Wild Cherry heavy fruiting tree by the entrance (flowers in April)
Wych Elm note the unsymmetrical leaves at the stalk end this identifies Elms. Nearly all the hedge on the left side of the tarmacd path from car park to Lagoon 2 contains Wych Elm, especially at the end by the pond.
Yew there are only two specimens on-site, both on Lagoon 2. Largest at South end, next to path.
Biting Stonecrop at top of seawall by Lagoon 1
Bladder Wrack commonest black seaweed along the shore
Common Cord Grass binds soft silt mud together at exposed side of salt-marsh
Marram Grass Taller, grey-green grass, on the land-side of saltmarsh.
The photo below is of the saltmarsh at Shepperdine, showing the two above grasses (with more commoner grasses on the seawall).
Common Saltmarsh-grass BRERC record, 31/12/1998
Sea Aster common succulent plant on saltmarsh with purple and yellow daisy-like flowers
Sea Club-rush, BRERC record 24/6/2009.
Sas Mayweed, BRERC record 16/6/2016.
Sea Milkwort on the seawall
Sea Wormwood, silver plant on the seawall by jetty (And BRERC record 24/6/2009).
Common Scurvygrass succulent plant on saltmarsh with white flowers starting in May.
Rock Samphire, BRERC record 31/12/1986.
Saltmarsh Rush, BRERC record 31/12/1998.
I can highly recommend the following website for identifying grasses - www.naturespot.org.uk.
Barren Brome by jetty.
Cock's-foot common along Severn Way sea-wall.
Common Bent, BRERC record 2/7/2002.
Common Couch - WWT survey Lagoon 3, 2019.
Common Reed the reeds in the large beds on Lagoons 2 & 3
Common Soft-brome common along Severn Way sea-wall.
Compact Rush, BRERC record 24/6/2009.
Creeping Bent, BRERC record 16/6/2016.
Creeping Soft-grass common along Severn Way sea-wall.
False Fox Sedge
False Oat-grass, BRERC record 16/6/2016.
Glaucous Sedge, BRERC record 16/6/2016.
Greater Pond-sedge in pond to south of Lagoon 3.
Grey Sedge (Carex Divulsa), BRERC record 2/7/2002.
Hairy Sedge, BRERC record 2/7/2002.
Hard Rush, BRERC record 16/6/2016.
Hard-grass, BRERC record 24/6/2009.
Long-bracted Sedge - WWT survey Lagoon 3, 2019.
Meadow Barley, BRERC record 24/6/2009.
Meadow Foxtail, BRERC record 24/5/2007.
Pampas-grass 2 clumps in middle of Lagoon 3.
Pendulous Sedge one large clump at south end of Lagoon 2.
Perennial Rye-grass common along Severn Way sea-wall.
Red Fescue, BRERC record 16/6/2016.
Reflexed Saltmarsh-grass common along Severn Way sea-wall.
Rough Meadow-grass, BRERC record 17/7/2011.
Sea Couch - WWT survey Lagoon 3, 2019.
Sharp Rush - WWT survey Lagoon 3, 2019.
Soft-rush, BRERC record 2/7/2002.
Sweet Vernal-grass, BRERC record 16/6/2016.
Sweet-grass, BRERC record 16/6/2016.
Yorkshire-fog common along Severn Way sea-wall.
Annual Meadow-grass, BRERC record 16/6/2016.
Crimson Wax Cap
Dog Vomit Slime Mold
Dung Fungus orange
Scarlet Elf Cap
St. George's Mushroom
Spectacular Rustgill Mushroom not edible
Taphrina alni (Alder Tongue)
Velvet Shank on stumps in mid-winter
Ash dieback fungus
Dutch Elm Disease Fungus
Earth Tongue Lagoon 3, Nov 2021
Field Blewit Lagoon 3, Dec 2021
No. of species = 362