Sium latifolium, Greater Water-parsnip
Great Water-parsnip Sium latifolium is Nationally Scarce, being found in 66 hectads (10 x 10 km squares) since 1970. It is Endangered, having declined by 60%, and is also listed in Section 41 of the NERC Act. It occurs scattered in south and east England with a stronghold in Somerset. It grows along ditch margins preferring slightly alkaline and high nutrient conditions. It is susceptible to competition, shading and also to grazing.
Historically 19 localities have been recorded in Oxfordshire (Druce 1927 and the Flora of Oxfordshire 1998), but despite searching former sites, only two are now known to be extant. Both populations were quite small, 26 at Wytham Ditches and Flushes SSSI and 22 at Burnt Mill Meadow, Marston, Local Wildlife Site.
By 2012 these numbers had declined. At Wytham the population dropped to 19 following an increase cattle grazing and competition from Common Reed. At Marston only nine plants could be found. Seed from both sites was sent to the Millennium Seed Bank, Kew.
Plants associated with Greater Water-parsnip at Burnt Mill Meadow
|Agrostis stolonifera||Creeping Bent||LA|
|Alopecurus pratensis||Meadow Foxtail||O|
|Carex otrubae||False Fox-sedge||R|
|Carex riparia||Greater Pond-sedge||LA|
|Carex sp. (sterile)||A sedge||LA|
|Deschampsia cespitosa||Tufted Hair-grass||O|
|Eleocharis palustris||Common Spike-rush||LA|
|Hordeum secalinum||Meadow Barley||O|
|Hottonia vulgaris||Water Violet||LA|
|Mentha aquatica||Water Mint||O|
|Persicaria amphibia||Amphibious Bistort||O|
|Oenanthe fistulosa||Tubular Water-dropwort||O|
|Phalaris canariensis||Reed Canary-grass||LF|
|Sium latifolium||Greater Water-parsnip||R|
|Stachys palustris||Marsh Woundwort||R|
|Vicia cracca||Tufted Vetch||R|
At Wytham the population was reinforced by plants grown by the Oxford University Botanic Garden from seed from the same site. This was combined with cutting and raking the reeds and the use of electric fences put up by the tenant (Farm Animal Initiatives) to protect the plants from cattle. However the fencing is movable so that grazing can be re-allowed to reduce the competition from dense growth of Common Reed. It was found that seed kept for more than one year failed to germinate though new plants could be obtained by taking root cuttings.
At Marston the population was been cleared of surrounding vegetation, but was then grazed off by muntjac. The adjacent field is grazed by sheep, which cannot control the coarse sedge growth in the water’s edge.
Work on this species has been funded by the Environment Agency and now by Natural England. Management work has been carried out by Farm Animal Initiatives on land owned by the University of Oxford. The Oxford Botanic Garden has raised and planted out plants for the reinforcement.