Ceratophyllum demersum L. and Fruit PerformanceAuthor(s): Mary J. P. ScannellSource: The Irish Naturalists' Journal, Vol. 18, No. 12 (Oct., 1976), pp. 348-349Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/25537967 .

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348

CERATOPHYLLUM DEMERSUM L. AND FRUIT PERFORMANCE Mary J. P. Scannell

Ceratophyllum demersum (hornwort) appears to fruit rarely in Ireland The Herbarium material, 26 specimens gathered between 1880 and 1975, is without fruit apart from one sheet with an undeveloped fruit-body labelled: "H 38: Down,

deep drains, Downpatrick, 23.8.1880 S. A. Stewart". Staminate flowers occur not infrequently, but the Seed Collection of the

Herbarium, largely the work of Praeger and Colgan, does not include seed of hornwort. In the literature references are few, Praeger (1938) quotes Templeton "In fructification in the lake at Ballinahinch, 23 Aug., 1808: Templeton Journal".

Detached pieces of C. demersum found on the lock gates of the Grand Canal, Ballsbridge, in 1970 constitute the first record of the species in County Dublin (Scannell, 1971). The material had been carried downstream. In the follow

ing years hornwort was observed to grow west of the lock gates at Huband bridge; by 1975 the colony had increased and was seen to dominate the submersed flora.

Large candelabra-like plants, tethered in position by fine strands of green algae now make up the vegetation where formerly Potamogeton crispus, Elodea canadensis, Groenlandia densa, Myriophyllum sp. and scattered clumps of

Sagittaria sagitiifolia comprised the plant community. Arber (1920) notes, "it is characteristic of hornwort to occur sometimes in such great abundance that it drives out nearly all other competitors".

In the summer months of 1975 (described as the warmest for 42 years, in the Dublin area), male flowers in some abundance were observed on the plants in the canal. The flowers, grouped 6-8 in a whorl in leaf axils, were readily

visible by colour contrast, pale green against the darker green of the plant body. On 19 July, two fruit structures in early formation were observed. As

vertical columnar forms, apricot red in colour, they were conspicuous near the

apex of a vegetative shoot. The gynoecium in C. demersum is a solitary carpel with one ovule.

Sampling to collect developed fruits was made at intervals in the following weeks. At the end of August hundreds of strands had been examined resulting in some 25-30 nuts. The smooth fruits were now a rich brown-green and measured

4 mm X 2 mm with a translucent foand 0.5 mm on the peripheral margin of the

laterally compressed shape. The dbtuse (not spinous) tubercles which occurred on the ridge of compression, curved downwards from the lower third of the fruit.

The apex terminated in a hooked projection, the remains of the spent stigma. End of season fragmentation of the plant had now set in and yet the canal fruits were not in accord with published descriptions "warty, beaked with spines". Further reading provided the answer, the canal fruits were not mature and were

unlikely to develop further. Arber (1920) describes hornwort as a curious plant isolated in its habit

and structure, "a plant in which the aquatic habit has reached its ultimate ex

pression". The stamens at maturity become detached, float upwards, dehisce at the surface, the pollen having a high specific gravity sinks, stigmas are fertilised, an ex

ample of water pollination. C. demersum is found throughout the world and there are indications

that its birthplace may have been in some more genial climate (Arber, 1920). Maturation of hornwort fruits in rivers and streams about the northern periphery of London was observed by H. B. Guppy between 1890-1893. In the hot summer of 1893, Guppy found the plant in ample fruit. He remarked, "although this plant often flowers in the heated shallows of ponds ... in this climate . . . it rarely matures its fruit. In various localities I have never found the fruit beyond the early stage. When ponds were low in water and were excessively heated the plants

matured their fruits in some quantity. ... the depth of water was a few inches, the water on occasions reaching 95?F. The thermal conditions for the maturation of the fruit can occur only in shallow ponds. Even in Fiji the fruit only matures in the superheated waters of shallow pools".

These observations of Guppy explains the performance of hornwort in the Grand Canal.

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349

In the British section of the Herbarium fruit is shown on three sheets. Fully developed red warty nuts occur on one, that collected by Alfred Freyer, No. 1256. in Huntingdonshire. Warren (de Tabley), in the Flora of Cheshire (1889), states that he had found fruit only once. In several county Floras (mostly British) complete fruit is often described with no further comment on frequency or matur ation. Gillham (1974) writing on seed dispersal by birds quotes Olney and provides a list of species eaten by foraging birds; C. demersum is amongst those listed.

Herbarium, National Botanic Gardens, Dublin. 9.

REFERENCES Arber, A. (1920) Water Plants'. A study of Aquatic Angiosperms. Cambridge; 84-90. Gill ham, M. E. (1974) Seed Dispersal in Birds. In The Flora of Changing Britain, ed. F.

Perring. BSB1.

Guppy, H. B. (1894) Water Plants and their wavs, Ceratophyllum demersum. Science-Gossip. 1. New Series: 195-199.

Praeger, R. LI. (1938) Flowering Plants in A Flora of the North-East of Ireland, 2nd Ed.

by Stewart and Corry. Scannell, M. J. P. (1971) Ceratophyllum dentersum L. in Co. Dublin. Ir. Nat. J. 17: 61.

MARINE FAUNA NOTES FROM THE NATIONAL MUSEUM OF IRELAND?III

C. E. O'Riordan

The following notes contain information concerning unpublished records of cetacean strandings on Irish coasts which were recently brought to the attention of the National Museum.

In February, 1973, Mr Patrick Fitzmaurice of the Inland Fisheries Trust forwarded photographs of a whalebone whale which was washed ashore near Annagh

Head on the Mullet Peninsula about 4 or 5 September, 1971. The photographs were passed to Dr P. E. Purves of the British Museum who suggested that the

specimen was an immature fin whale (common rorqual). Mr Robert Nash of the Ulster Museum informed us that a common

porpoise was stranded at Whitecliffs near Portrush, Co. Antrim, on 18 August, 1975. Its identity was determined by the staff of the Ulster Museum.

Dr P. J. H. van Bree of the Zoologisch Museum, Universiteit van Amster dam supplied me with details of the following four cetacean strandings on the coast

of Co. Galway. A Cuvier's whale (Ziphius cavirostris), probably female, was

stranded north of Mace Head, Co. Galway (L 7332) about 1969. A female common

por noise (Phccoena phocoena) was taken in a salmon net in Galway Bay off Barna

in June, 1971. Its total length was 160 cm <5ft3in). Another specimen, probably a male, was found in a state of decomposition at Galway Harbour on 23

September, 1974. The circumstances of its occurrence in the harbour are not

known. A pilot whale (Globicephala malaend) was. found at Stmthpoint, Inishnee

Island, near Roundstone, Co. Galway, on 29 December, 1974- The skulls of these

cetaceans were recovered by Dutch visitors to Ireland, and brought to Holland.

The pilot whale skull was deposited in the Rijksmuseum van Natuurlijke Historic Leiden (RMNH), and the skulls of the Cuvier's whale and porpoises were deposited in the Zoologisch Museum, Amsterdam (ZMA).

A 21 ft cetacean, toothed in both jaws, was stranded at Culoort, Malin

Head, Co. Donegal (C 4156) on 12 November, 1973. In late September, 1975, a

cetacean about 8 to 12 feet in length was seen stranded on the shore near the old

Geneva Barracks between Passage East and Woodstown in Waterford Harbour

(S 7008). A headless cetacean carcase measuring 8 ft 6 in was found near Dooagh Strand, Achill, on 4 July, 1975. Due to lack of detailed information it was not

possible to identify these last three cetaceans.

On 16 September, 1972, Captain W. F. J. Morzer Bruyns of Bussum, Netherlands, visited the north side of Inishtreh Island, Bertraghboy Bay, Co. Galway (L 7437). and discovered a few weathered cetacean bones scattered around. Though a number had previously been removed by souvenir hunters, he recovered a piece

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