Flora of Ashdown Forest - Botanical Society of the British Isles

140penetrate the host tissues, releasing enzymes allowing it to obtain water and nutrients, which also causes aproliferation of new growth in the host to which the parasite can spread. Once established the dodder roots die.The threads branching from anyone point are different lengths which is believed to maximise its chances ofstriking another host. The effects upon host growth vary from necrosis of shoots and impaired flowering in U/exminor, to discoloration of the growing shoots in Cal/una. The reddish colour of heather attacked by dodder is quitenoticeable late in the season on some rides on the Forest.C. epithymum has been recorded parasitising numerous plants; van Ooststroom (1951) noted 91 hosts inGotland, Sweden. The hosts on Ashdown Forest have been recorded for populations in seven sites:Host species Sites Host species SitesCa//una vulgaris 717 Potentilla erecta 2/7Deschampsia f/exuosa 317 Danthonia decumbens 117Erica cinerea 317 Ga/ium saxatile 117Molinia caeru/ea 317 Pedicularis sy/vatica 117Vlex minor 317 Pteridium aquilinum 117Festuca filiformis 217 Rubus fruticosus agg. 117These compare well with hosts previously recorded on the Forest (cf. above), but it almost always occurs onCa//una and spreads onto other plants from there, and is sometimes only weakly attached to grasses. Theinteresting one is Pedicularis sy/vatica which is itself a semi-parasite on the roots of other plants, so it isn't onlyfleas which have smaller fleas!On chalk grassland dodder is predominantly found on legumes such as Trifolium, Lotus and Medicago. Thedodders on chalk grassland are generally bigger and more branched with paler, larger flowers with shorter styles,and have been described as var. trifolii Bab. Seedlings taken from plants parasitising V/ex minor failed to grow onclovers suggesting that these races are physiologically different too and this may explain why Trifolium, Lotus andMedicago on the Forest are not parasitised (host specificity is known in other parasites such as mistletoe). Someof the morphological variation between the two races may be related to the differing nutrition available from thehosts; the luxuriant growth of var. trifolii could reflect the increased nitrogen levels in the hosts which havenitrogen-fixing bacteria in their roots, although this would be expected in Vlex on heathland too, or perhaps anadaptation to parasitising clonal patches of clover rather than isolated heath land shrubs.Although commonly thought of as an annual regenerating each year from seed, Shillito (1952) demonstratedthat C. ephhymum can over-winter on woody hosts by means of tubercles. These organs appear as tiny scales onthe host above the haustoria and develop after the stems die back in late autumn. The following spring theydevelop new stems which grow and infect more plants, giving an instant early start to the dodder. This is almostcertainly the main form of perennation on Ashdown Forest since patches can be found in exactly the samelocation from year to year, usually on Cal/una, provided the rides have not been mown too short. The role oftubercles in var. trifolii would be interesting to investigate on chalk grasslands since the availability of overwinteringperennial hosts is less than on heathlands, and also in the related C. europaea which typically parasitisesVrtica and Humulus on riverbanks.Locally common in southern Britain and most of Europe, and in temperate Asia and North Africa.MENYANTHACEAEMenyanthes trifoliata. Bogbean.Near Coleman's Hatch, B. B. Gough; near Crow's Nest, Camp Hill, E. M. Day;Poundgate, A. G. Gregor (Wolley-Dod 1937). Ashdown Forest, 1942, L. M. Child(TLS). A number of references to Chelwood and Duddleswell, with a note to golooking for it before the end of May (Dent 1928-1953). Chelwood Gate (42.30),3 1955, and near Nutley, 1957, R. A. Boniface (BRC). West of Fairwarp, in theColeman's Hatch area, at Upper Chuck Hatch and at Newbridge Bog, 1950s, FR.Tetrads 42N, 42P, 42T and 43F (Hall 1980).4 5 Large patches in pond at Chelwood Vachery (430.295), 1994, TR, MR & PR;small patch in wet boggy flush near Londonderry Farm (445.292), 1992 +, NM et al.,and another at 444.292, 1992, NM which appeared following re-introduction of the grazing in 1989, possiblyfrom buried seed or perhaps just more visible when the grass was eaten; lakes in Pippingford Park (44.30 and44.31), 1993 +, Flora meetings but gone from pond in 44.31 where it was last recorded in 1987, R. Fitzgerald etal.; bog west of Airman's grave (458.297), 1991, CM; small pond east of Old Lodge (467.297), 1992, NM & CM.Scattered in Sussex and south-east England and decreasing (Rich & Woodruff 1996), though still widespreadand common in the north and west. Widespread in Europe except near the Mediterranean, Asia, Morocco,Greenland and North America.