Flora of Ashdown Forest - Botanical Society of the British Isles

35DRYOPTERIDACEAEPolystichum aculeatum.3 ++------'-1-4 5Hard shield-fern.Tetrads 42T and 43H (Hall 1980), the latter may be outside the Flora area.One plant in the sunken lane at Fairwarp 1474.267), pH 4.3, 1995, PD, the same tetradas Hall's 42T record.Its occurrence in Sussex predominantly on sandy soils noted by Hall (1980) and confirmedby our record and observations of it on sand rocks outside the Forest contrasts with its ecologyin Britain as a whole, where Jermy et al. (1978) note it requires a base-rich substrate, though itis certainly common on limestone and base-rich places in the north and west of Britain. It isquite widespread in Britain and western Europe, becoming rarer eastwards, also found in NorthAfr'lca and Asia.Polystichum setiferum. Soft shield-fern.Tetrads 33V, 42P, 43H and 43Z (Hall 1980).Our records are scattered around the edges of the Forest, where it either occurs as singleplants on the north side at the Plaw Wood stream (390.332) and on the track at Rystwood(437.343), or more locally frequent along river banks in the deeper shaded gullies around3 ++------'"'-/-- Fairwarp and the stream east of Black Hill. It also occurs in abundance on the west side of theA22 cutting at Nutley (442.283), a dangerous place to record it.Damp shaded stream sides on alluvial soils and sunken lanes are its usual habitat inSussex where it can be locally common, but surely not restricted to base-poor soils as4 5suggested by Jenny et al. (1978)?It is a southern sub-Atlantic species of south and west Europe and other temperate areas which reaches its northernlimit in Scotland. It occurs most frequently in south and west Britain where it is warm and wet in winter, and this mayexplain why it is commonest in our deeper wooded stream valleys and sunken lanes.Both Polystichum species were noted as increasing in England by the BSBI Monitoring Scheme (Rich & Woodruff1996) which may be due to relaxed cutting regimes in hedges (FR, pers. comm. 1990).Dryopteris filix-mas. Male-fern.Common on the Forest (Hall 1980).We have recorded it from most squares except the high open areas on the east side ofthe Forest.It is one of the most common and widespread ferns in Sussex and Britain, with broad3ecological requirements, though most abundant in woods and often in hedges. It is commonand widespread in Europe, Asia, Madagascar and the Americas.4 5Dryapteris affinis (D. barreri). Scaly male-fern.Common on the Forest (Hall 1980).We recorded it less frequently than D. filix-mas, but it is none the less quite widespread especially on the poorer soilsin wooded areas in the middle of the Forest, and sometimes on the hedgebanks. It is abundant in woodlands on the westside of lakes in Pippingford Park, but more often occurs as a few plants scattered here and there. In Britain it is muchcommoner 'In the west, and is also quite western 'In distribution in Europe.D. affinis has arisen by hybridisation between D. filix-mas and the montane D. oreades, but reproduces from sporesproduced asexually so distinctive forms may be locally frequent. This fern is a taxonomic nightmare, and although threesubspecies are generally recognised there may be at least eight taxa in the group. Rob Cooke has determined all ourrecords for the subspecies, of which we have two: subsp. borreri is the commonest one and tends to occur on the morefertile soils, whilst subsp. affinis is much rarer and occurs on the more acidic soils. Subsp. cambrensis is western inBritain and is unlikely to occur here. The maps of the subspecies are obviously incomplete.Drvopteris affinis subsp. affinis subsp. borred3 +I-----"'--.;;,.j- 3 -t-Ic---------..-"'nl-4 5 4 5 4 5