Island Life Part 24

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 pal.u.s.tris, _var._ RADICANS; Polygala vulgaris, _var._ GRANDIFLORA; Cerastium arctic.u.m, _var._ EDMONSTONII; Trifolium repens, _var._ TOWNSENDII; Rosa involuta, _var._ WILSONI; Rubus fruticosus, _sub-sp._ LONGITHYRSIGER; Campanula rotundifolia, _var._ SPECIOSA; Erythraea centaurium, _sub-sp._ LATIFOLIA; Carex involuta, (? Hyb.); Carex vesicaria, _var._ GRAHAMI; Deyeuxia neglecta, _var._ HOOKERI.

_Five_ of comparatively well limited species. Arabis petraea, _var._ GRANDIFOLIA; Helianthemum guttatum, _var._ BREWERI; Geranium sanguineum, _var._ LANCASTRIENSE; Oenanthe Ph.e.l.landrium, _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 {364} 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 compet.i.tion 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 sh.o.r.es of Mediterranean).

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

{365} 12. _Pinguicula grandiflora._ S. W. Ireland (Spain, Pyrenees, Alps of France and Switzerland).

13. _Neotinea intacta._ W. Ireland (S. France, Portugal, Spain, and sh.o.r.es of Mediterranean).

14. _Spiranthes romanzoviana._ S. W. Ireland (North America).

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

16. _Potamogeton lonchites._ Ireland, Mr. Arthur Bennett informs me that this is certainly not British or European, but may possibly be identical with _P. fluitans_ _var._ _America.n.u.s_ of the U. States.

17. _Potamogeton kirkii_ (_natans_ sub.-sp.). W. Ireland. (Arctic Europe?)

18. _Eriocaulon septangulare._ W. Ireland, Skye, Hebrides (North America).

19. _Carex buxbaumii._ N. E. Ireland, on an island in Lough Neagh (Arctic and Alpine Europe, North America).

20. _Deyeuxia neglecta_ (_var._ _Hookeri_). On the sh.o.r.es and islands of Lough Neagh. (And in Germany, Arctic Europe, and North America.)

We find here nine south-west European species which probably had a wider range in mild preglacial times, and have been preserved in the south and west of Ireland owing to its milder climate. It must be remembered that during the height of the glacial epoch Ireland was continental, so that these plants may have followed the retreating ice to their present stations and survived the subsequent depression. This seems more probable than that so many species should have reached Ireland for the first time during the last union with the continent subsequent to the glacial epoch. The Arctic, Alpine, and American plants may all be examples of species which once had a wider range, and which, owing to the more favourable conditions, have continued to exist in Ireland while becoming extinct in the adjacent parts of Britain and Western Europe.

As contrasted with the extreme scarcity of peculiar species among the flowering plants, it is the more interesting and unexpected to find a considerable number of peculiar mosses and Hepaticae, some of which present us with phenomena of distribution of a very remarkable character. For the following lists and the information as to the distribution of the genera and species I am indebted to Mr. William Mitten, one of the first authorities on these beautiful little plants. That of the mosses has been corrected for this edition by Dr. R. Braithwaite, and several species of hepaticae have been added by Mr. Mitten. {366}

LIST OF THE SPECIES OF MOSSES AND HEPATICae WHICH ARE PECULIAR TO THE BRITISH ISLES (OR NOT FOUND IN EUROPE).

(_Those belonging to non-European genera in Italics._)

MOSSES.

1. Systegium Mittenii South England.

2. Campylopus Shawii North Britain.

3. ,, setifolius Ireland, Wales, and Hebrides.

4. Seligeria calcicola South England.

5. Pottia viridifolia South England.

6. Leptodontium recurvifolium Ireland and Scotland.

7. Tortula Hybernica Ireland.

8. _Streptopogon gemmascens_ Suss.e.x.

9. Bryum barbatum Scotland.

10. _Bartramidula Wilsoni_ Ireland, Wales, and Scotland.

11. _Daltonia splachnoides_ Ireland, Antilles, and Mexico.

12. _Hookeria laetevirens_ Ireland, Cornwall, and Madeira.

13. Hypnum micans Ireland.

14. Myurium Hebridarium Hebrides and Atlantic Islands.

15. Hedwigia ciliata _var._ striata Wales and Scotland.

HEPATICae.