Elodea nuttallii (Planch.) St John in IrelandAuthor(s): David SimpsonSource: The Irish Naturalists' Journal, Vol. 21, No. 11 (Jul., 1985), pp. 497-498Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/25538955 .

Accessed: 15/06/2014 02:10

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact support@jstor.org.

.

Irish Naturalists' Journal Ltd. is collaborating with JSTOR to digitize, preserve and extend access to The IrishNaturalists' Journal.

http://www.jstor.org

This content downloaded from 62.122.79.52 on Sun, 15 Jun 2014 02:10:09 AMAll use subject to JSTOR Terms and Conditions

Ir. Nat. J. Vol. 21 No. 11 1985 497

ELODEA NUTTALLII (PLANCH.) ST JOHN IN IRELAND

David Simpson

School of Botany, Trinity College, Dublin 2

Elodea nuttallii (Planch.) St John is a close relative of the well-known aquatic species Elodea canadensis Michx. (Canadian pondweed), and in common with the latter is a native of North America. Over the past 18 years E. nuttalliihas become widespread in Gt. Britain,

having first been discovered in a canal near Oxford in 1966 (OXF). Until recently the only material known in Ireland was from a pond in the National Botanic Gardens, Glasnevin, Co Dublin, vc H21, the material at Renvyle, W Galway, vc H16 which was once assigned to this species (Tutin 1962, Scannell and Synnott 1972) having later been redetermined as

Hydrilla verticillata (L.f.) Royle by Scannell and Webb (1976). However, in October 1984 whilst botanising with Dr John Parnell, I found E. nuttallii on the western side of Lough Neagh near Drumenny, Co Tyrone, vc H36 (H9677). lt was growing in a small, man-made harbour, and was well-established on soft mud in c. 0.2-1.5m of water. The water was

heavily polluted with engine oil. No other species were present. Further material was found stranded along the shoreline at Ardboe Point (H9676), c. 2km to the south, suggesting that the plant occurs in the Lough at some distance from the shore. E. canadensis was also found

at this second site, together with Lemna gibba L., Potamogeton perfoliatus L. and

Potamogeton pectinatus L. Specimens of ?. nuttallii from the first site have been deposited in TCD. Visits were also made to the shore at Ballyronan and along the eastern side of the

Lough near Glenavy, but neither of the Elodea species were seen. E. nuttallii is a highly variable plant, and in some cases can be confused with E.

canadensis. It is best distinguished by its linear or linear-lanceolate leaves which have

narrowly acute or acuminate apices, together with at least some leaves strongly recurved

and twisted. E. canadensis has leaf shape ranging from linear-oblong to oval, but rarely linear-lanceolate and never linear. The leaf apices are usually broadly acute or obtuse, never

strongly recurved and rarely twisted. The axilliary scale character given by Tutin (op. cit.) is only of use in separating Elodea from Hydrilla; both Elodea species have entire axillary scales, whilst in Hydrilla they are fringed.

In Britain E. nuttallii has become dominant in many sites. This has often been at the

expense of E. canadensis and in some cases the former has completely replaced the latter

where it was once the dominant species. The reasons for this are not entirely clear, but

experimental work (Simpson 1983) suggests that E. nuttallii has a faster rate of growth under certain conditions, which may give it a competitive advantage over E. canadensis. In

any case there is every possibility that E. nuttallii will spread rapidly in Ireland. It becomes

particularly weli-established in canals, slow-moving rivers and loughs where the water is

nutrient-rich.

Two points of interest arise from the discovery of the Lough Neagh plants: how did the

plants arrive in Lough Neagh. and do these or the Glasnevin plants represent the first record of the species in Ireland? One of the major difficulties with Elodea is attempting to identify methods of its dispersal. A particular problem is that it often becomes established in widely separated and unconnected water-bodies. Seed dispersal must be ruled out as the plant only reproduces vegetatively in the British Isles. Many other agencies have been suggested, but the two most plausible are introduction by Man or waterfowl. In the first case ?. nuttallii is sometimes used as an ornamental plant in aquaria and garden ponds, so it is possible that

unwanted material has been discarded into the lake. In Gt. Britain this has probably aided the spread of both Elodea species and may account for the occurrence of related exotic

species, such as Egeria densa Planch, and Lagarosiphon major (Ridley) Moss as casuals.

Alternatively waterfowl might have carried small pieces of E. nuttallii, trapped in their

feathers, over from Gt. Britain, which then became free and established itself in the lough. Elodea does have minute teeth along the leaf margins which might enable the plant to cling

This content downloaded from 62.122.79.52 on Sun, 15 Jun 2014 02:10:09 AMAll use subject to JSTOR Terms and Conditions

498 Ir.Nat.J. Vol. 21 No. 11 1985

to birds' feathers. Indeed, Pearsall (1921) offered this suggestion to explain the occurrence of Hydrilla verticillata at Esthwaite Water in Gt. Britain, a locality well-separated from the nearest known stations in eastern Europe. Unfortunately, despite the speculation, it is

unlikely that the precise method of introduction will ever be known.

Regarding the second point, it was indicated by Simpson (1984) that the Glasnevin

plants validly represented the first Irish record. However, it appears that the plants were found in a pond containing exotics (M. J. P. Scannell pers. comm. 1984) and not, as was

originally believed, in a naturally vegetated pond outside the gardens. In view of this, the Glasnevin material cannot be considered as the first record for the species, and this distinction should now apply to the Lough Neagh plants.

Acknowledgements

Thanks are due to Professor David Webb and Dr John Parnell for helpful discussion.

REFERENCES

Pearsall, W. H. (1921) A short note on Hydrilla verticillata. J. Bot. Lond. 59: 235.

Scannell, M. J. P. & Synnott, D. M. (1972) Census Catalogue of the Flora of Ireland. Stationery Office, Dublin.

Scannell, M. J. P. & Webb, D. A. (1976) The identity of the Renvyle Hydrilla. Ir. Nat. J. 18: 327-331.

Simpson. D. A. (1983) Experimental Taxonomic Studies o/Elodea Michx in the British Isles. Ph.D. Thesis,

University of Lancaster.

-(1984) A short History of the Introduction and Spread oiElodea Michx in the British Isles. Wat sonia 15:

1-9.

Tutin, T. G. (\962)Elodea, in Clapham, A. R., Tutin, T. G. & Warburg, E. F. Flora of the British Isles. C.U.P.,

Cambridge.

SYMPHYTUM ASPERUM LEPECHIN ? A NEW IRISH SPECIES

J. Parnell

School of Botany, Trinity College, Dublin 2

Plants of the genus Symphytum are moderately common throughout Ireland ? two

species and a hybrid have been recorded (Scannell and Synnott 1972). The commoner

species is Symphytum officinale L. which occurs in 19 out of 40 Irish vice-counties. The

hybrid between it and Symphytum asperum Lepechin, Symphytum x uplandicum Nyman is the commonest Irish Symphytum and is recorded from 28 vice-counties though S. asperum itself has not been recorded from Ireland at all (Scannell and Synnott op. cit.). The other

species, Symphytum tuberosum L. is far less common, only being recorded from six vice-counties.

Recently, whilst on field-work in the west of Ireland with E. R. and J. T. M. Parnell, I came across a plant oi Symphytum asperum growing in a hedgebank beside the road leading to the Lake Isle of Innisfree, near Lough Gill, Co Sligo, G7732. The identity of the

specimen, now in TCD, has been kindly confirmed for me by Dr F. H. Perring. I have studied specimens in both TCD and DBN and can find no other specimens

which can undoubtedly be referred to S. asperum though one is undoubtedly very closely allied. This specimen is from the Lough Bunny region, Co Clare (in TCD). It differs from true S. asperum in its rather short anther filaments, more or less apetiolate upper leaves and

slightly decurrent middle and lower leaves, it may represent either an odd variant of S.

asperum or a backcross of S. x uplandicum with S. asperum.

S. asperum and S. X uplandicum are both thought to have been introduced by man for fodder. The fact that the hybrid is so widespread is explained, at least for British material,

by extensive vegetative spread (Perring 1968, Perring in Stace 1975). Probably a similar

explanation applies here. However, one major difference is that whilst this is the first record

This content downloaded from 62.122.79.52 on Sun, 15 Jun 2014 02:10:09 AMAll use subject to JSTOR Terms and Conditions