Island Life; Or, The Phenomena and Causes of Insular Faunas and Floras

1. Limnea involuta.—A pond snail with a small polished amber-coloured shell found only in a small alpine lake and its inflowing stream on Cromagloun mountain near the lakes of Killarney. It was discovered in 1838, and has frequently been obtained since in the same locality. It is sometimes classed as a variety of Limnea peregra, and is at all events closely allied to that species.

2. Hydrobia jenkinsii.—A small shell of the family Rissoidæ inhabiting the Thames estuary both in Essex and Kent. It was discovered only a few years ago, and was first described in 1889.

3. Assiminea grayana.—A small estuarine pulmonobranch found on the banks of the Thames between Greenwich and Gravesend, on mud at the roots of aquatic plants. It has been discovered more than sixty years.

But besides the above-named species there are a considerable number of well-marked varieties of shells which seem to be peculiar to our islands. A list of these has been kindly furnished me by Mr. Theo. D. A. Cockerell, who has paid much attention to the subject; and after omitting all those whose peculiarities are very slight or whose absence from the continent is doubtful, there remain a series of forms some of which are in all probability really endemic with us. This is the more probable from the fact that an introduced colony of Helix nemoralis at Lexington, Virginia, presents numerous varieties among which are several which do not occur in Europe.136 The following list is therefore given in the hope that it may be useful in calling attention to those varieties which are not yet positively known to occur elsewhere than in our islands, and thus lead, ultimately, to a more accurate knowledge of the facts. It is only by obtaining a full knowledge of varieties, their distribution and their comparative stability, that we can ever hope to detect the exact process by which nature works in the formation of species.

List of the Species and Varieties of Land and Freshwater Shells which, so far as at present known, are believed to be Peculiar to the British Isles or not found on the ContinentLimacidæ

1. Limax marginatus, var. maculatus. Ireland; frequent, very distinct.

2.     ,,           ,,          ,,   decipiens. Ireland and England.

3.     ,,      flavus, var. suffusus. England; Melanic form.

4.     ,,          ,,      ,,   griseus. England; Melanic form.

5. Agriolimax agrestis, var. niger. Yorkshire. Melanic. Azores.

6.        ,,            ,,        ,,   griseus. England. Melanic.

7. Amalia gagates, var. rava. W. of England.

8.      ,,    sowerbyi, var. rustica. England.

9.      ,,          ,,         ,,   nigrescens. Surrey and Middlesex.

10.    ,,          ,,         ,,   bicolor. Ealing.

11. Hyalina crystallina, var. complanata. Near Bristol.

12.      ,,     fulva, var. alderi.

13. Vitrina pellucida, var. depressiuscula. S. England, Wales.

Helicidæ

14. Arion ater, var. albo-lateralis. England, Wales, Isle of Man; very distinct.

15.    ,,    hortensis, var. fallax. England. Common at Boxhill.

16. Geomalacus maculosus. Kerry and Cork. Three varieties have been described, one of which occurs in Portugal.

17. Helix aspersa, var. lutescens. England. Not rare perhaps in France.

18.    ,,    nemoralis, var. hibernica. Ireland.

19.    ,,    rufescens, var. manchesteriensis. England.

20.    ,,    hispida, var. subglobosa. England.

21.    ,,        ,,        ,,   depilata. England.

22.    ,,        ,,        ,,   minor. England, Ireland.

23.    ,,    granulata, var. cornea. Lulworth, Dorset.

24.    ,,    virgata, var. subaperta. Bath.

25.    ,,        ,,        ,,   subglobosa. England, Wales, Bantry Bay.

26.    ,,        ,,        ,,   carinata. Wareham, Dorset.

27.    ,,    caperata, var. major. England, Wales, Scotland. Distinct.

28.    ,,          ,,        ,,   nana. England.

29.    ,,          ,,        ,,   subscalaris. Wales, Ireland.

30.    ,,          ,,        ,,   alternata. England, Kent.

31.    ,,    acuta, var. nigrescens. England.

Pupidæ

32. Pupa anglica, var. pallida. Not rare.

33.    ,,    lilljeborgi, var. bidentata. Ireland.

34.    ,,    pygmea, var. pallida. Dorset and Devon.

35. Clausilia rugosa, var. parvula. Ireland.

Stenogyridæ

36. Cochlicopa lubrica, var. hyalina. Wales, Scotland.

37. Cœcilianella acicula, var. anglica. England.

Succineidæ

38. Succinea putris, var. solidula. Wiltshire.

39.      ,,       virescens, var. aurea. Ireland.

40.      ,,       pfeifferi,     ,,   rufescens. England, Ireland.

41.      ,,            ,,          ,,   minor. England.

Limnæidæ

42. Planorbis fontanus, var. minor. England.

43.      ,,       carinatus,   ,,   disciformis. England.

44.      ,,       contortus,  ,,   excavatus. Ireland.

45.      ,,            ,,         ,,   minor.

46. Physa fontinalus, var. oblonga. England, Wales, Ireland.

47. Limnæa involuta. Ireland.

48. Limnæa glutinosa, var. mucronata.

49.      ,,      peregra, var. burnetti. Scotland. Very distinct.

50.      ,,           ,,       ,,   lacustris. Perhaps in C. Verde Islands.

51.      ,,           ,,       ,,   maritima. Great Britain.

52.      ,,           ,,       ,,   lineata. England.

53.      ,,           ,,       ,,   stagnaliformis. England.

54.      ,,      stagnalis, var. elagantula. Curious. In a pond at Chislehurst.

55.      ,,      palustris, var. conica. England, Ireland.

56.      ,,            ,,        ,,   tincta. England, Wales.

57.      ,,            ,,        ,,   albida. England.

58.      ,,      truncatula, var. elegans. England, Ireland. Distinct.

59.      ,,             ,,         ,,   fusca. Wales.

60. Ancylus lacustris, var. compressus. England.

Paludinidæ

61. Paludina vivipara, var. efasciata. England. Not uncommon.

62.       ,,          ,,        ,,   atropurpurea. Pontypool.

Rissoidæ

63. Hydrobia jenkinsii. Thames Estuary.

64.        ,,        ventrosa, var. minor.

65.        ,,             ,,         ,,   decollata.

66.        ,,             ,,         ,,   ovata.

67.        ,,             ,,         ,,   elongata.

68.        ,,             ,,         ,,   pellucida.

Cyrenidæ

69. Sphærium corneum, var. compressum.

70.        ,,            ,,         ,,   minor.

71.        ,,            ,,         ,,   stagnicola.

72.        ,,      ovale, var. pallidum. England.

73.        ,,      lacustre, var. rotundum. Wales.

74. Pisidium pusillum, var. grandis.

75.       ,,          ,,         ,,   circulare. Wales.

76.       ,,     nitidum, var. globosum.

Unionidæ

77. Unio tumidus, var. richensis. Regent's Park. Peculiar form.

78.    ,,   pictorum, var. latior. England.

79.    ,,       ,,          ,,   compressus. England.

80.    ,,   margaritifer, var. olivaceus.

81. Anodonta cygnæa, var. incrassata. England.

82.        ,,           ,,        ,,   pallida. England, Ireland.

Estuarine or Marine Pulmonotranchs

83. Assiminea grayana. Thames Estuary.

Peculiarities of the British Flora.—Thinking it probable that there must also be some peculiar British plants, but not finding any enumeration of such in the British Floras of Babington, Hooker, or Bentham, I applied to the greatest living authority on the distribution of British plants—the late Mr. H. C. Watson, who very kindly gave me the information I required, and I cannot do better than quote his words: "It may be stated pretty confidently that there is no 'species' (generally accepted among botanists as a good species) peculiar to the British Isles. True, during the past hundred years, nominally new species have been named and described on British specimens only, from time to time. But these have gradually come to be identified with species described elsewhere under other names—or they have been reduced in rank by succeeding botanists, and placed or replaced as varieties of more widely distributed species. In his British Rubi Professor Babington includes as good species, some half-dozen which he has, apparently, not identified with any foreign species or variety. None of these are accepted as 'true species,' nor even as 'sub-species' in the Students' Flora, where the brambles are described by Baker, a botanist well acquainted with the plants of Britain. And as all these nominal species of Rubi are of late creation, they have truly never been subjected to real or critical tests as 'species.'"

In my first edition I was only able to name four species, sub-species, or varieties of flowering plants which were believed to be unknown on the continent. But much attention has of late years been paid to the critical examination of British plants in comparison with continental specimens, and I am now enabled to give a much more extensive list of the species or forms which at present seem to be peculiar. For the following list I am primarily indebted to Mr. Arthur Bennett of Croydon. Sir Joseph Hooker has been so kind as to examine it carefully and to give me his conclusions on the relative value of the differences of the several forms, and Mr. Baker, of Kew, has also assisted with his extensive knowledge of British plants.

List of Species, Sub-species, and Varieties of Flowering Plants found in Great Britain or Ireland, but not at present known in Continental Europe. By Arthur Bennett, F.L.S. The most distinct and best determined forms are marked with an asterisk.

1. *Caltha radicans (Forst.). "A much disputed species, or form of C. palustris. It is a relatively rare plant." (J. D. H.) "Certainly distinct from the Scandinavian form." (Ar. Bennett.)

2. *Arabis petræa (Lam.) var. grandifolia (Druce). Scotch mountains. "The larger flowers alone distinguish this." (J. D. H.)

3. Arabis ciliata (R. Br.). In Nyman's Conspectus Floræ Europææ this species is given as found in England and Ireland only. "A very much disputed form of a plant of very wide distribution in Europe and North America." (J. D. H.)

4. Brassica monensis (Huds.). "This and the continental B. cheiranthus (also found in Cornwall) are barely distinguishable from one another." (J. D. H.)

5. Diplotaxis muralis (D. C.) var. Babingtonii (Syme). South of England. "A biennial or perennial form; considered to be a denizen by Watson." (J. D. H.)

6. *Helianthemum guttatum (Mill), var. Breweri (Planch). Anglesea. "Very doubtful local plant. H. guttatum (true) has lately been found in the same locality." (J. D. H.)

7. *Polygala vulgaris (L.), var. grandiflora (Bab). Sligo, Ireland. "A very distinct variety." (J. D. H.)

8. Viola lutea (Huds.), var. amœna (Symons). "V. lutea itself is considered to be a form of V. tricolor, and V. amœna the better coloured of the two forms of V. lutea." (J. D. H.)

9. *Cerastium arcticum (Lange), var. Edmonstonii (Beeby). Shetland Is. "But C. arcticum is referable to the very variable C. alpinum." (J. D. H.) "Near to the European C. latifolium." (Ar. Bennett.)

10. *Geranium sanguineum (L.), var. Lancastriense (With.). Lancashire. "A prostrate local form growing out of its native soil in sand by the sea." (J. D. H.) Mr. Bennett writes: "I have grown G. sanguineum and its prostrate variety in sand, and neither became Lancastriense."

11. Genista tinctoria (L.), var. humifusa (Dickson). Cornwall. "A decumbent hairy form confined to the Lizard." (J. D. H.)

12. Cytisus scoparius (Link.), var. prostratus (Bailey). Cornwall. "A prostrate form." (J. D. H.)

13. Anthyllis vulneraria (L.), var. ovata (Bab.). Shetland Is. "A slight variety." (J. D. H.)

14. *Trifolium repens (L.), var. Townsendii (Bab.). Scilly Isles. "A well-marked form by its rose-purple flowers. Confined to the Scilly Isles." (J. D. H.)

15. *Rosa involuta (Sm.), var. Wilsoni. (Borrer.) Wales. "There are a multitude of forms or varieties of R. involuta, and R. wilsoni is one of the best-marked, found on the Menai Straits and Derry." (J. D. H.)

16. Rosa involuta var. gracilis (Woods). "This is considered by many as one of the commonest forms of R. involuta." (J. D. H.)

17. Rosa involuta var. Nicholsoni (Crepin). "Another slight variety of R. involuta." (J. D. H.)

18. Rosa involuta var. Woodsiana (Groves). "A Wimbledon Common variety of R. villosa." (J. D. H.)

19. Rosa involuta var. Grovesii (Baker). "Mr. Baker thinks this of no account." (J. D. H.)

20. Rubus echinatus (Lind.). "A variety of the widely spread R. Radula, itself a form of R. fruticosus." (J. D. H.)

21. *Rubus longithyrsiger (Lees). "Mr. Baker informs me that this is a very distinct plant never yet found on the continent." (J. D. H.)

22. Pyrus aria (Sm.) var. rupicola (Syme). "A very local form, confined to Gt. Britain, and owing its characters to its starved position." (Baker.)

23. Callitriche obtusangula (Le Gall), var. Lachii (Warren). Cheshire. "This is intermediate between two sub-species of C. verna." (J. D. H.)

24. *Œnanthe fluviatilis (Coleman). South of England. "The fluitant form of Æ. Phellandrium." (J. D. H.)

25. Anthemis arvensis (L.), var. anglica (Spreng). N. Coast of England. "A maritime form with more fleshy leaves formerly found near Durham. It has other very trifling characters." (J. D. H.)

26. Arctium intermedium (Bab.). "There are two sub-species of A. lappa, majus and minus, each with varieties, and this is one of the intermediates." (J. D. H.)

27. Hieracium holosericium (Backh.). Scotch Alps.

28. H. gracilentum (Backh.).                     ,,

29. H. lingulatum (Backh.).                       ,,       A var. of this in Scandinavia.

30. H. senescens (Backh.).                       ,,

31. H. chrysanthenum (Backh.).               ,,

32. H. iricum (Fr.). Teesdale and Scotland.

33. H. gibsoni (Backh.). Yorkshire and Westmoreland.

34. Hieracium nitidum (Backh.). Lower glens of the Scotch Alps. Mr. Bennett writes:—"The following Hieracia have been named by Mr. F. J. Hanbury as endemic forms. One can only safely say they are certainly not known in Scandinavia, as they have all been submitted to Dr. Lindeberg. But usually Scotch species are not represented in Central Europe to any great extent, though several do occur. Still these new forms ought to be critically compared with all Dr. Peters' new species."

35. H. Langewellense (Hanb.). Caithness.

36. H. pollinarium (Hanb.). Sutherland.

37. H. scoticum (Hanb.). Sutherland and Caithness.

38. H. Backhousei (Hanb.). Aberdeen, Banff, Inverness.

39. H. caledonicum (Hanb.). Caithness and Sutherland.

40. H. Farrense (Hanb.). Sutherland and Shetland Is.

41. H. proximum (Hanb.). Caithness. With regard to all these Hieracia Sir Joseph Hooker and Mr. Baker say:—"No case can be made of these. They are local forms with the shadowest of shady characters." Mr. Bennett writes: "H. iricum and H. Gibsoni are the best marked forms."

42. *Campanula rotundifolia (L.), var. speciosa (A. G. More). W. Ireland. "Very well distinguished by its large flowers and small calyx lobes, approaching the Swiss C. Scheuzeri." (J. D. H.)

43. Statice reticulata (Sm.). "Baker agrees with me that this is also a Mediterranean species." (J. D. H.)

44. Erythræa capitata (Willd.), var. sphærocephala (Towns.). Isle of Wight. "A form of E. centaurium utterly anomalous in its genus in the insertion of the stamens. A monster rather than a species." (J. D. H.)

45. *Erythræa latifolia (Sm.). On the sandy dunes near Liverpool. "A local form." (J. D. H.)

46. Myosotis collina (Hoffim.), var. Mittenii (Baker). Sussex.

47. Veronica officinalis (L.), var. hirsuta (Hopk.). Ayr, Scotland.

48. Veronica arvensis (L.), var. eximia (Towns.). Hampshire.

49. Mentha alopecuroides (Hull). Nearest to M. dulcissima (Dum.).

50. Mentha pratensis (Sole). Only once found.

51. Chenopodium rubrum (L.), var. pseudobotryoides (H. C. Watson).

52. Salix ferruginea (Forbes). England, Scotland. "Probably a hybrid between S. viminalis and S. cinerea." (J. D. H.)

53. Salix Grahami (Borr.). Sutherland, Perth. "A hybrid?" (J. D. H.)

54. Salix Sadleri (Syme). Aberdeen. "A hybrid?" (J. D. H.)

55. *Spiranthes Romanzoviana (Cham.). Ireland (N. America).

56. *Sisyrinchium angustifolium (Mill.). Ireland. (Arctic and Temp. N. America.)

57. Allium Babingtonii (Borrer). West England, West Ireland. "A form of A. ampeloprasum, itself a naturalised species." (J. D. H.)

58. *Potamogeton lanceolatus (Sm.). Anglesea, Cambridgeshire, Ireland. Mr. Bennett writes:—"Endemic! I have taken a good amount of trouble to ascertain this. Nearly 400 specimens I have distributed all over the world with requests for information as to anything like it. The response is everywhere the same, 'nothing.' The nearest to it occurs in the Duchy of Lauenberg but is referable to P. heterophyllus."

59. Potamogeton Griffithii (Ar. Bennett). Carnarvon. "Nearest to this is a probable hybrid from N. America, but not identical." (Ar. Bennett.)

60. Potamogeton pusillus (L.), sub-sp. Sturrockii (Ar. Benn.). Perth.

61. Potamogeton pusillus (L.), var. rigidus (Ar. Benn.). Orkneys, Shetlands.

62. Ruppia rostellata (Koch.), var. nana (Bosw.). Orkneys.

63. *Eriocaulon septangulare (With.). Hebrides, Ireland. N. America.

64. Scirpus uniglumis (Link), var. Watsoni (Bab.). Scotland, England. "This is a variety of a sub-species of the common S. palustris." (J. D. H.)

65. Luzula pilosa (Willd.), var. Borreri (Bromf).

66. *Carex involuta (Bab.). Cheshire. "A distinct enough plant but probably a hybrid between C. vesicaria and C. ampullacea, found in one place only." (J. D. H.)

67. Carex glauca (Murr.), var. stictocarpa (Sm.). Scotland.

68. Carex precox (Jacq.), var. capitata (Ar. Benn.). Ireland. "A remarkable plant (monstrosity?) simulating C. capitata (L.)." (Ar. Bennett.)

69. *Carex Grahami (Boott). "A mountain form of C. vesicaria." (J. D. H.)

70. *Spartina Townsendi (Groves). Hampshire. "A distinct but very local form of S. stricta, found in one place only." (J. D. H.)

71. Agrostis nigra (With.).

72. Deschampsia flexuosa (Trin.), var. Voirlichensis (J. C. Melvill). Perth.

73. *Deyeuxia neglecta (Kunth), var. Hookeri (Syme). Ireland. "A distinct variety confined to Lough Neagh." (J. D. H.)

74. Glyceria maritima (Willd.), var. riparia (Towns.). Hampshire.

75. Poa Balfouri (Bab.). Scotland. "An alpine sub-variety of a variety of the protean P. nemoralis." (J. D. H.)

In his comments on this extensive list of supposed peculiar British plants, Sir Joseph Hooker arrives at the following conclusions:—

1. There are four unquestionably distinct species which do not occur in continental Europe: viz.—

One absolutely endemic species, Potamogeton lanceolatus.

Three American species, Sisyrinchium angustifolium, Spiranthes romanzoviana, Eriocaulon septangulare.

2. There are sixteen endemic varieties of British species, viz.—

Eleven of more or less variable species, Caltha palustris, var. radicans; Polygala vulgaris, var. grandiflora; Cerastium arcticum, var. edmonstonii; Trifolium repens, var. Townsendii; Rosa involuta, var. wilsoni; Rubus fruticosus, sub-sp. longithyrsiger; Campanula rotundifolia, var. speciosa; Erythræa centaurium, sub-sp. latifolia; Carex involuta, (? Hyb.); Carex vesicaria, var. Grahami; Deyeuxia neglecta, var. Hookeri.

Five of comparatively well limited species. Arabis petræa, var. grandifolia; Helianthemum guttatum, var. Breweri; Geranium sanguineum, var. Lancastriense; Œnanthe Phellandrium, var. fluviatilis; Spartium stricta, var. Townsendi.

The above twenty species are marked in the list with an asterisk. Of the remaining fifty-five, Sir Joseph Hooker says, "that for various reasons it would not be safe to rely on them as evidence. In most cases the varietal form is so very trifling a departure from the type that this may be safely set down to a local cause, and is probably not constant. In others the plant is doubtfully endemic; in still others a hybrid."

Even should it ultimately prove that of the whole number of the fifty-five doubtful forms none are established as peculiar British varieties, the number admitted after so rigorous an examination is about what we should expect in comparison with the limited amount of speciality we have seen to exist in other groups. The three American species which inhabit the extreme west and north-west of the British Isles, but are not found on the continent of Europe are especially interesting, because they demonstrate the existence of some peculiar conditions such as would help to explain the presence of the other peculiar species. Whether we suppose these American forms to have migrated from America to Europe before the glacial epoch, or to be the remnants of a vegetation once spread over the north temperate zone, we can only explain their presence with us and not further east by something favourable either in our insular climate or in the limited competition due to our comparative poverty in species.

About half of the peculiar forms are found in the extreme west or north of Britain or in Ireland, where peculiar insular conditions are at a maximum; and the influence of these conditions is further shown by the number of species of West or South European plants which occur in the same districts.

We may here notice the interesting fact that Ireland possesses no less than twenty species or sub-species of flowering plants not found in Britain, and some of these may be altogether peculiar. As a whole they show the effect of the pre-eminently mild and insular climate of Ireland in extending the range of some south European species. The following list of these plants, for which I am indebted to Mr. A. G. More, with a few remarks on their distribution, will be found interesting:—

List of Irish Flowering Plants which are not found in Britain

1. Polygala vulgaris (var. grandiflora). Sligo.

2. Campanula rotundifolia (var. speciosa). W. Ireland.

3. Arenaria ciliata. W. Ireland (also Auvergne, Pyrenees, Crete).

4. Saxifraga umbrosa. W. Ireland (also Pyrenees, N. Spain, Portugal).

5.        ,,      geum. S. W. Ireland (also Pyrenees).

6.        ,,      hirsuta. S. W. Ireland (also Pyrenees).

7. Inula salicina. W. Ireland (Scandinavia, Middle and South Europe).

8. Erica mediterranea. W. Ireland (W. France, Spain, Portugal).

9.     ,,   mackaiana (tetralix sub.-sp.) W. Ireland (Spain).

10. Arbutus unedo. S. W. Ireland (W. of France, Spain, Portugal and shores of Mediterranean).

11. Dabeocia polifolia. W. Ireland (W. of France, Spain and Portugal).

12. Pinguicula grandiflora. S. W. Ireland (Spain, Pyrenees, Alps of France and Switzerland).

13. Neotinea intacta. W. Ireland (S. France, Portugal, Spain, and shores of Mediterranean).

14. Spiranthes romanzoviana. S. W. Ireland (North America).

15. Sisyrinchium angustifolium. W. Ireland (North America, Arctic and Temp.).