Drosera anglica Huds. (= D. longifolia L.)
Great Sundew

Account Summary

Growth form and preferred habitats

Mature plants of D. anglica are distinguished from D. intermedia (Oblong-leaved Sundew), by their proportionally narrower leaves which have a blade up to 5 cm long, the stiffer nature of the plant overall, the presence of glandular hairs on the petioles and by the flowering stem being up to twice as long as the leaves and arising centrally (though sometimes bent at the base and arising more at one side). The leaves are much more erect or ascending than those of D. intermedia and they do not form a flattened, or even a definite rosette compared with those of D. rotundifolia (Round-leaved Sundew), from which they also very obviously differ in shape and size.

Apart from inhabiting the very wettest conditions on Atlantic ombrogenous acid peat bog surfaces, which offer nutrient-starved growing conditions dependent upon dust brought down by rainfall (including raised, valley and blanket bog types), D. anglica appears to avoid any degree of shade, which also helps to distinguish it from the ecologically more tolerant D. rotundifolia. It does not tolerate any degree of burial in peat, nor even partial overgrowth in Sphagnum hummocks.

Great Sundew also frequents somewhat more nutrient-rich sites than the other two Sundew species. This occurs only in somewhat drier, climatically more continental parts of Britain − including conditions of lime- or base-rich fens. Although there is no scientific analysis available to prove it (see Crowder et al. 1990, p. 256), this appears probably more to do with water supply than nutrient levels, since what D. anglica really demands is a constantly moist substrate. It is often found growing in standing water in bog pools and it tolerates being submerged. Flushing of bogs and fens with groundwater springs supplies this irrigating moisture requirement, which would be particularly significant in the drier regions of B & I.

Webb & Scannell (1983) comment on the very remarkable and unique occurrence in an Irish context of D. anglica growing in highly calcareous fens on the N & E shores of Gortachalla Lough, NNW of Galway. This is replicated in some English base-rich fens and Webb recounts seeing the species growing on pure calcareous marl in Gotland, SE Sweden (Webb & Scannell 1983, p. 81).

In other parts of B & I, D. anglica may rarely be found growing on lakeshore sands or on river gravel (Crowder et al. 1990).

Variation

No varieties are recognised in B & I, although in the Alps and in Arctic Europe small forms with just one or two flowers are sometimes referred to as var. pusilla Kihlm, or forma minor Abromeit (Crowder et al. 1990; Sell & Murrell 2018).

Fermanagh occurrence

There are records of D. anglica in the Fermanagh Flora Database from a total of 42 tetrads, 8% of those in the VC. It remains sufficiently frequent in Fermanagh to be described as occasional and it is quite widespread, mainly in the more upland W of the county. It is still present (or at least it was once recorded) in 29 post-1975 tetrads. However, the tetrad map suggests a definite decline of this species during the last 40 years.

D. anglica has more limited ecological tolerances than D. rotundifolia (Round-leaved Sundew) and in Fermanagh it grows in the wettest parts of bog pools and hummock surfaces. It tends to be either submerged in the middle of intermittent pools, or occurs around the margins of more permanent bog pools, or beside soakaways, the flushed seepage areas of valley bogs. It is also found in damp hollows on blanket bogs and more rarely and more sparsely in open areas on wet heaths.

Insect capture, plant nutrition and performance

The larger leaves of D. anglica can catch more insects simultaneously than D. rotundifolia can manage, but while the leaf surface and its trapping hairs react more quickly, digestion is less complete. Such differences in nutrition may eventually help explain the contrasting pH tolerances of the three Sundew species, a topic which otherwise remains a mystery comparable with the differing ecological behaviour of Schoenus nigricans (Black Bog-rush) in Irish bogs and British fens.

Deleterious effects of disturbance, drainage and drought

On account of its more strictly defined hydrological requirements and especially an absolute intolerance of dry conditions, D. anglica is even more sensitive and vulnerable to drainage than the other Sundew species. The greatly disturbed habitat that is left after mechanical peat cutting using a sub-surface boring auger, is extremely detrimental to the survival of this species: the pre-existing water table is hugely disrupted and the shallow roots of D. anglica are completely unable to maintain the plants in these conditions. Of the three Drosera species we are dealing with here, D. anglica is by far the most susceptible to drought, being confined to hollows that never completely dry out on bogs and wetter heaths.

Reproduction

The floral biology of D. anglica is similar to that described for D. rotundifolia (see that account) and a detailed summary is provided by Crowder et al. (1990).

Seed longevity

Fortunately Drosera seeds appear to have a dormant survival period in the soil seed bank of several years, eg, up to 5 years in both D. intermedia and D. rotundifolia. There does not yet seem to be any estimate of this for D. anglica in the literature and no records for any Sundew from sites in B & I (Thompson et al. 1997).

Colonising ability

In common with D. rotundifolia, seedlings of D. anglica display colonising ability on bare, wet peat surfaces. Typically D. anglica roots in either wet peat or in Sphagnum moss and while the plant can tolerate flooding for periods of up to two months, it never forms dense mats of plants under these conditions in the manner of D. intermedia (Oblong-leaved Sundew). Rather it tends to occur singly or in small groups.

British and Irish occurrence

The New Atlas map shows that D. anglica is increasingly confined to N and W parts of Scotland and Ireland, with scarce outliers in Cumbria and coastal parts of W Wales, southern England and East Anglia. The species has suffered a major decline in both B & I, but it has been much more drastic and widespread in England than in SE & E Ireland. This difference can undoubted be attributed to the particular sensitivity of D. anglica to operations involving drainage, peat-cutting and burning of bogs and wet heaths. Nowadays D. anglica, which is more confined to lowland situations than D. rotundifolia, is much more predominantly northern and western in its distribution on both islands than was previously the case (Preston et al. 2002).

European and world occurrence

D. anglica has a more restricted European range than D. rotundifolia, being absent from Iceland and much less widespread in France. It is rare in N Spain, ± absent from the Mediterranean basin and rapidly thins east of Switzerland (Jalas et al. 1999, Map 2963). Again, compared with D. rotundifolia, it is less extensive and more discontinuous in Asia although it does reach Japan and Kauai Island in the Hawaiian group (Crowder et al. 1990). D. anglica is also circumpolar and in N America is widespread in the more northern regions from coast to coast. However, it does not penetrate as far south on the continent as D. rotundifolia does (Hultén & Fries 1986, Map 1000).

Threats

Drainage and cutting of peat bogs.

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