Flora of Ashdown Forest - Botanical Society of the British Isles

61Dolygonum arenastrum. Equal-leaved knotgrass.Tetrad 43H (Hall 19801.Usually a plant of trampled areas, especially car parks and gateways.under-recorded, and certainly so in Sussex (Hall 1980).It is widespread in Britain but under-recorded, Asia and temperate Asia.Probably a little4 5*Fallopia japonica (Reynoutria japonica). Japanese knotweed.Common on the Forest (Hall 19801.We have widely recorded it from roads ides, waste ground and stream sides, and it seemsto be spreading. It produces little seed (none in two populations examined on the Forest) andspreads very effectively by roots and rhizomes, thus often introduced with soil on roads ides,or washed down rivers. Some patches now cover several hundred square metres.It is a vigorous species native in the lava fields in Japan and the Far East. Conolly(1977) has described its spread in Britain. It was first introduced as an ornamental gardenplant in 1825. It may be a little restricted by climate; it is affected by frost and possibly4 5 drought, but unfortunately usually recovers rapidly.This and Heracleum mantegazzianum are the two vascular plants that it is illegal to introduce into the wild yet it is stillincreasing (Rich & Woodruff 1996). It can grow through tarmac, paving and stonework, and is a considerable nuisance onriver banks. Its shoots can grow 4 cm a day in the spring, and it rapidly swamps other vegetation. Once established it isdifficult to eradicate, and in areas with sensitive wildlife requires three good doses of glyphosate or 2,4~D. with follow-upspot treatment. It can also be controlled by regular cutting, or intensive grazing by sheep or goats.On the Forest war has been declared on Japanese knotweed and a control programme implemented. It is controlled inabout 16 sites by a combination of cutting and spraying. Small areas of young plants can be pulled out by hand, which islabour intensive but works well. as at the entrance to the Ashdown Forest Centre car park. On larger patches if newgrowth is caught early in the year, spraying with glyphosate and a wetting agent can be effective. Larger, taller patchesare first cut, and then sprayed when the regrowth is about 0.5 metres high, which is not only easier to do but the youngerfoliage absorbs the spray better. Absolute control can be achieved but requires effort over several years.*Fal/opia x bohemica (F. japonica x sachalinensis). Bohemian knotweed.Verge bank below a garden on the 82188 (509.3221, 1993, PW.This hybrid is becoming more widely recognised and recorded in Britain. It has oftenbeen mistaken as F. japonica; useful leaf outlines showing the consistently cordate leaf basesare given in Rich & Rich (19881.3 -++--------'-+-4 5*Fal/opia sachalinensis {Reynoutria sachalinensis}. Giant knotweed.Recorded in tetrad 33W (Hall 19801 but possibly outside our area.One large clump near the entrance to Posthorn Lane, Forest Row (435.347), 1993, TR;car park at St John's (504.315), 1991, PW, and hopefully eradicated by spray in 1994/5.Rarely established in Sussex where it has been thrown out of gardens or crept under the3 fences of its own accord, and most often naturalized now in wet places on stream banks.Probably first introduced from the Far East, as a fodder plant; it is now scattered throughoutlowland Britain (Conolly 1977).4 5