FOOTNOTES:
[1]Not El Araisch, SSW. of Tangier on the Atlantic coast, but some place in the interior, and N. of the city of Marocco.
[2]This is no doubt Elæoselinum humile (Ball), which we found near or at the above defined locality. Ball formed a very decided opinion that Jackson’s plant, whether the true Ammoniacum or not, was a species of Elæoselinum.
[3]It is mentioned under this name by Homer in his description of the Island of Calypso. See Daubeny On the Trees and Shrubs of the Ancients, p. 42.
[4]See Cook’s Sketches in Spain, vol. i. p. 5 (1831); and Loudon’s Gardener’s Magazine, Ser. ii. vol. iii. p. 522.
[5]See Bostock’s translation of Pliny, vol. iii. p. 194, &c.
APPENDIX E.
On the Canarian Flora as compared with the Maroccan.
By Joseph Dalton Hooker.
In respect of their botanical relationship to neighbouring Continents, Islands or Archipelagos may be roughly classed under two divisions: namely, those which are situated within a moderate distance of continents, and whose Floras are manifestly derived from them or have had a common origin with theirs; and those which are situated very far from any continents, and whose Floras differ so much either from that of the neighbouring continent or from that of those parts of the continent that are nearest to them, that their origin is a matter of speculation. Of the first division, the British Isles, and probably Vancouver’s Island, in North-West America, are conspicuous instances, their Floras being almost identical with those of the neighbouring continents. St. Helena, the Galapagos, Mauritius, and the Sandwich Islands are instances of the opposite extreme, for their Floras differ widely from those of any continents.
Between these extreme cases there are many intermediate ones; and there are others of an exceptional character, as Iceland, which, though far removed from any part of Europe, has but one flowering plant not found on that continent (Platanthera hyperborea); and Ceylon, which though it is almost united to the Peninsula of Hindostan, yet in many respects differs greatly from that peninsula in its Flora.
Amongst the exceptional cases to continental proximity being accompanied by close botanical relationship is the Flora of the Canarian Archipelago, which differs so greatly from that of the northern part of its neighbouring continent, namely, from that of Marocco,[1] that it demands notice in any work treating of the vegetation of the latter country.
This diversity between the Maroccan and Canarian Floras has been pointed out in Ball’s ‘Introductory Observations to the Spicilegium Floræ Maroccanæ,’[2] where it appears that whilst Marocco, out of 1,627 species of flowering plants, contains 165 endemic plants, it has only 15 which are confined to it and to the Canaries, or to it and Madeira. And Ball goes on to remark (p. 301), in respect of these few species common to both Floras: ‘I think it is safe to say that the facts rather tend to show the accidental diffusion of a few Macaronesian[3] species on the adjacent coast of Africa, than to indicate the direct connection between the continent and those islands within a geological period at all recent.’
Were this diversity due solely or chiefly to the Canaries wanting many Maroccan plants, the inquiry would not be a pressing one; but as to this deficiency is to be added the presence in the Canaries of many indigenous species, and even several genera[4] which are absent in Marocco, and in Marocco the great rarity of endemic genera, of which Argania only is arboreous, the inquiry becomes a very important one, inviting a much closer study than can here be given to it.
The Flora of the Canarian Archipelago, though consisting, like the Maroccan, for the most part of Mediterranean species, yet differs from that of Marocco, in containing many plants that may be classed under the following categories:—
I. It contains many non-Maroccan plants, obviously introduced by man, and not from Europe only, but from various parts of both the Old and New Worlds. This will not appear surprising when it is remembered that Teneriffe was for several centuries the Prime Meridian of Geographers and the resort of all the European ocean-navigators, who took their departure from it on their outward voyages, and made for it on their homeward ones. The Alternanthera achyrantha, a tropical American plant, was no doubt imported into the Canaries, and possibly from thence introduced into Spain (where it is now naturalised). Argemone mexicana is another, and there are still other as conspicuous examples of such foreign introductions. This maritime intercourse can, however, only partially account for the remarkable disproportion between the number of probably introduced plants in the Canaries and in Marocco; and we must take into account the isolation, barbarism, and exclusiveness of the latter country, and the absence of any commercial intercourse between it and the Canaries or the rest of the world.
In Webb and Berthelot’s ‘Phytographia Canariensis’ upwards of fifty plants are enumerated as to which we have little doubt that all have been introduced by man, and none of which have hitherto been found in Marocco. The list includes many weeds of the widest tropical and temperate distribution, as species of Sida, Waltheria, Siegesbeckia, Bidens, Lippia, Physalis, Nicandra, Euphorbia, Alternanthera, Commelyna, and various Cyperaceæ, and Grasses.
II. The Canaries contain many apparently indigenous plants, which, though not Maroccan, are widely distributed elsewhere; these form a large class, and the following are some of the most prominent of them:—
| Delphinium Staphysagria | Fragaria vesca |
| Hypecoum procumbens | Pyrus Aria |
| Biscutella auriculata | Prunus lusitanica |
| Viola canina | Epilobium palustre |
| Silene Behen | Anthemis fœtida |
| „ nutans | „ coronopifolia |
| Rhus Coriaria | Cynara horrida |
| Spartium junceum | Lactuca sylvestris |
| Ulex europæus | Cressa cretica |
| Medicago arborea | Calamintha Nepeta |
| Trigonella hamosa | Atriplex glauca |
| Trifolium striatum | Euphorbia serrata |
| „ squarrosum | „ obliquata |
| „ suffocatum | „ Lagascæ |
| „ filiforme | Orchis longibracteata |
| Lotus angustissimus | Ophrys tabanifera |
| Vicia hirsuta | Iris pallida |
| Lathyrus odoratus | Lilium candidum |
| Alchemilla arvensis |
together with various Cyperaceæ, Grasses and water-plants, some of which, and of the above, will no doubt hereafter be found in Marocco.
III. They contain some quite peculiar plants which are more closely allied to endemic species of Marocco than to those of any other country, and may have been derived from species that originally were transported from that country. These are but few, and are almost confined to species of the genus Monanthes, which is limited to these countries and the Cape de Verde Islands, of Cactoid Euphorbiæ, of succulent Sonchi, and of the Kleinia division of Senecio.
IV. They contain plants not found hitherto in Marocco, and which are more closely allied to Mediterranean species than to any others; and these form a very large class. The data for a complete list would require a very careful comparison of the Maroccan species with the species described in the ‘Phytographia’ and discovered since, many of which are unquestionably founded on too slight or too variable characters.[5]
It will be sufficient for present purposes to contrast the results obtained from a selection of genera[6] taken for comparison from Ball’s ‘Spicilegium’ with the same from Webb’s ‘Phytographia’:—
| Genera | Canary Islands | Marocco | ||
|---|---|---|---|---|
| Number of species in each | Species confined to Canaries | Number of species in each | Species confined to Marocco | |
| Hypericum | 8 | 7 | 7 | 0 |
| Matthiola | 4 | 3 | 3 | 0 |
| Cistus | 2 | 1 | 7 | 0 |
| Helianthemum | 6 | 3 | 14 | 0 |
| Polycarpia | 6 | 4 | 1 | 0 |
| Sempervivum | 23 | 23 | 1 | 1 |
| Cytisus | 11 | 9 | 11 | 4 |
| Lotus | 10 | 6 | 14 | 2 |
| Dorycnium | 3 | 3 | 1 | 0 |
| Rhamnus | 3 | 3 | 3 | 0 |
| Ilex | 2 | 2 | 0 | 0 |
| Chrysanthemum | 12 | 12 | 11 | 4 |
| Senecio | 9 | 5 | 11 | 1 |
| Doronicum | 5 | 5 | 0 | 0 |
| Tolpis | 5 | 4 | 2 | 0 |
| Sonchus | 17 | 12 | 6 | 0 |
| Convolvulus sect. Rhodorhiza | 5 | 5 | 0 | 0 |
| Echium | 12 | 10 | 9 | 1 |
| Micromeria[7] | 17 | 17 | 1 | 0 |
| Sideritis | 6 | 5 | 7 | 2 |
| Teucrium | 3 | 1 | 11 | 4 |
| Solanum | 6 | 2 | 2 | 0 |
| Scrophularia | 5 | 3 | 9 | 1 |
| Digitalis | 2 | 2 | 2 | 0 |
| Statice | 9 | 9 | 13 | 3 |
| Plantago | 10 | 3 | 11 | 1 |
| Beta | 3 | 2 | 1 | 0 |
| Euphorbia | 19 | 9 | 22 | 6 |
| Ephedra | 3 | 2 | 2 | 0 |
| Juniperus | 2 | 1 | 4 | 0 |
| Pinus | 1 | 1 | 1 | 0 |
| Ruscus | 2 | 2 | 1 | 0 |
| Asparagus | 5 | 4 | 6 | 1 |
| Scilla | 4 | 4 | 9 | 0 |
| Luzula | 3 | 3 | 1 | 0 |
| 243 | 187=¾ | 204 | 31=⅙ | |
The disproportion between the two Floras in the case of these selected genera is thus well shown. It is most remarkable; the number of endemic species being in the Canaries three-fourths of the whole and in Marocco only one-sixth; and were the peculiar genera of the Canaries added, the disproportion would of course be increased.
The total number of Canarian species enumerated by Webb and Berthelot is about 1,000, of which 367,[8] or more than one-third, are regarded as peculiar to the Archipelago (a very few only of these being also Madeiran); whereas out of 1,627 Maroccan species only 165, or a little over one-tenth, are peculiar. Future discoveries will probably not materially increase the Maroccan proportion of peculiar species; whereas since the publication of Webb’s ‘Phytographia’ many peculiar species (especially of Statice and Crassulaceæ) have been discovered in the Canaries, and but few species common to other countries; and these additions will go far to neutralise any error introduced into the estimate, due to the great number of new species founded on insufficient data which the ‘Phytographia’ includes.
Under this head also should be included the peculiar Canarian genera that appear to be modifications of continental ones. They are Bencomia, closely allied to Poterium, of which there are two species, both confined to one Island (Teneriffe); one of these is also a native of Madeira, where only two individual trees, a male and a female, have ever been seen! Gesnouinia, allied to Parietaria; and Canarina, a monotypic genus allied to Campanula, but having a baccate fruit. Bosea, also a monotypic plant, is wholly unlike any known genus, and is, in some respects, intermediate between the two very distinct natural families—Chenopodiaceæ and Phytolacceæ.
V. Many Canarian plants are representatives of Floras more distant than those of Marocco or Western Europe, and are not found in those countries. These form an exceedingly interesting group, and may be classed according to countries thus:—
a. Oriental.—These are chiefly Arabo-Egyptian, but some of them extend even into Western India, and a few are representatives of tropical India. Some will no doubt yet be discovered in Marocco, especially south of the Atlas; and it is not unreasonable to suppose that such have crossed Africa in a subtropical latitude, and thus reached the Canaries under conditions now operating.
The most remarkable are the following. The genera in capitals have not hitherto been found in Marocco:—
| Polycarpon succulentum | Campylanthus salsoloides |
| Visnea Moccanera | Traganum nudatum |
| Gymnosporia cassinoides | Apollonias barbusana |
| Trigonella hamosa | Euphorbia Forskählii |
| Senecio flavus | Dracæna Draco |
| Ceropegia dichotoma |
Of the above hardly any have been found west of the Levant, or anywhere between Egypt and the Canaries, except, possibly, in Southern Algeria. Traganum must be reckoned as an African and Oriental desert type, and will probably be found in South Marocco; but Ceropegia is mainly Indian, as is Gymnosporia (Catha cassinoides, Webb). Campylanthus consists of the Canarian species, of a variety or closely allied one in the Cape de Verde Islands, and of a third which extends from Southern Arabia to Scinde. The nearest ally of the Apollonias (Phœbe barbusana, Webb) is a Ceylon tree; and Visnea is nearly allied to the Malayan genus Anneslea. Dracæna Draco is the most interesting of all in the list; for, though the genus abounds in tropical Africa, the Canarian form, which is also a native of the mountains of the Cape de Verde Islands, has only one near ally, the D. Ombet, which is confined to Abyssinia, Southern Arabia, and the intervening Island of Socotra.
b. The peculiar species representing American types inhabiting the Canaries or Madeira, but not found in Marocco, are in some respects even more remarkable than the Oriental.
They belong to the following genera:—
Bowlesia[9] (Drusa oppositifolia, DC.), Clethra, five species of Bystropogon, and Cedronella. Of these Bowlesia is otherwise confined to the tropical Andes of America, one species only extending as far north as Mexico; the Canarian species, which according to Webb is found on rocky shaded places in Teneriffe, from the sea-level to the wooded region, is most closely allied to a Peruvian one. Clethra is a genus which extends from South Brazil to the Northern United States, and is also found in Japan and the Malayan Archipelago. The Macaronesian species most resembles a North American; it is found also in Madeira. Bystropogon is, like Bowlesia, an Andean genus, extending from Peru to Columbia. All the Canarian species belong to a different section from the Andean, and there is one species of the same section in Madeira. Cedronella is a North American and Mexican genus, and the Canarian species differs from all its congeners in its trisect leaves; it is also Madeiran.
Of the Canarian Laurineæ, Persea indica, also a native of Madeira and the Azores, belongs to an American section of that large genus.
c. Tropical and South African types in the Canaries. Of these the most noticeable are two forest trees, belonging to the large tropical genus Myrsine. One of these, M. excelsa (Heberdenia excelsa, Banks) is also found in Madeira; the other, M. canariensis, is confined to the island whose name it bears. The tropical order Sapotaceæ, to which Argania belongs, has no representative in the Canaries, but has one in the Sideroxylon Mermulana of Madeira.
The only almost exclusively South African genus[10] in the Canaries is a species of Lyperia, of which there are numerous Cape of Good Hope species, and one doubtful one in the Somali country (North-East Africa). The widely diffused Cape shrub, Myrsine africana, is found in the Azores and in Abyssinia, but not in the Canaries, Cape de Verdes, Madeira, or Marocco. The two singular shrubs Phyllis and Plocama, consisting each of a single species, of which the Phyllis is found also in Madeira, are representatives of the Anthospermeæ, a very large and conspicuously South African and Australian tribe of Rubiaceæ, and of which the only Maroccan representative is Putoria, a Mediterranean genus of a single species, and which is not Canarian.
The Oreodaphne fœtens of the Canaries and Maderia is now[11] referred to the American, Madagascar, and South African genus Ocotea, and is most nearly allied to a species found in the latter country.
The Maroccan flowering plants are thus grouped by Ball in his ‘Spicilegium Maroccanum’[12]:—
| Total number of Maroccan species | 1.627 |
| Species widely diffused, temperate or tropical | 467 |
| Of which there are common to Marocco and the Islands | 300 |
| Maroccan, but not Insular | 167 |
| Mediterranean species in Marocco | 995 |
| Of which there are widely spread species common to the Islands and Marocco | 254 |
| Confined to Marocco and the Islands | 15 |
| Mediterranean species in Marocco, but not in the Islands | 726 |
| Maroccan species exclusively | 165 |
The proportion of Monocotyledons to Dicotyledons is in Marocco 1 to 4·6, in the Canaries 1 to 6—a very great difference.
The leading natural orders in Marocco and the Canaries respectively are:—
| Marocco Species | Canaries Species | |
|---|---|---|
| Compositæ | 208 | 143 |
| Leguminosæ | 189 | 104 |
| Gramineæ | 134 | 77 |
| Umbelliferæ | 86 | 27 |
| Labiatæ | 81 | 59 |
| Cruciferæ | 73 | 29 |
| Caryophylleæ | 69 | 38 |
In each country these seven natural orders include nearly half the Dicotyledonous plants. But in the Canaries the Crassulaceæ with 31 species should replace the Cruciferæ, and the Umbelliferæ be excluded.
The natural orders which are indigenous to the three Archipelagos of the Canaries, Madeira, and the Azores, but which are absent in Marocco, and the reverse are:—
| In the Archipelago, but not in Marocco. | In Marocco, but not in the Archipelago. |
|---|---|
| Simarubeæ (Cneorum) | Berberideæ |
| Pittosporeæ | Capparideæ |
| Ternstrœmiaceæ | Polygaleæ |
| Ilicineæ | Ampelideæ |
| Myrsineæ | Coriarieæ |
| Phytolacceæ (Bosea) | Saxifrageæ |
| Myriceæ | Apocyneæ |
| Commelyneæ (introduced?) | Lentibularieæ |
| Nyctagineæ | |
| Ulmaceæ | |
| Cupuliferæ | |
| Ceratophylleæ | |
| Alismaceæ | |
| Juncagineæ | |
| Melanthaceæ |
In the above lists the Commelyneæ are most probably introduced by man into the Canaries, and the absence of Lentibularineæ, Ceratophylleæ, Alismaceæ, and Juncagineæ in the Archipelago may be due to the want of suitable localities. The total absence of Cupuliferæ in all the Macaronesian Archipelago is inexplicable; and of Quercus especially, a genus so prominently developed in number of species and individuals on both continents, and which further abounds in both the Pliocene and Miocene beds of Europe.
The apparently indigenous Macaronesian genera which are wanting in Marocco are the following. Those in capitals are confined to the Canaries, or to the Canaries and Madeira:—
| Malvaceæ |
| Abutilon |
| Cruciferæ |
| Parolinia |
| Barbarea |
| Simarubeæ |
| Cneorum |
| Celastrineæ |
| Gymnosporia |
| Sapindaceæ |
| Melianthus? |
| Leguminosæ |
| Spartium |
| Ulex |
| Rosaceæ |
| Bencomia |
| Alchemilla |
| Fragaria |
| Aquifoliaceæ |
| Ilex |
| Pittosporeæ |
| Pittosporum |
| Ternstrœmiaceæ |
| Visnea |
| Umbelliferæ |
| Todaroa |
| Rubiaceæ |
| Phyllis |
| Plocama |
| Compositæ |
| Chrysocoma |
| Allagopappus |
| Vieræa |
| Doronicum |
| Serratula |
| Prenanthes |
| Campanulaceæ |
| Musschia |
| Canarina |
| Wahlenbergia |
| Ericeæ |
| Clethra |
| Asclepiadeæ |
| Ceropegia |
| Convolvulaceæ |
| Cressa |
| Boragineæ |
| Tournefortia |
| Labiatæ |
| Bystropogon |
| Cedronella |
| Verbenaceæ |
| Lippia |
| Solaneæ |
| Nicandra |
| Scrophularineæ |
| Campylanthus |
| Lyperia |
| Acanthaceæ |
| Justicia |
| Oleineæ |
| Notelæa |
| Myrsineæ |
| Myrsine |
| Sapotaceæ |
| Sideroxylon |
| Primulaceæ |
| Pelletiera |
| Chenopodieæ |
| Traganum |
| Laurineæ |
| Persea |
| Apollonias |
| Ocotea |
| Phytolacceæ |
| Bosea |
| Urticeæ |
| Gesnouinia |
| Myriceæ |
| Myrica |
| Aroideæ |
| Dracunculus |
| Liliaceæ |
| Dracæna |
| Cyperaceæ |
| Fimbristylis |
| Cladium |
| Gramineæ |
| Chloris |
| Tricholæna |
There are in Marocco, out of a total of 517 genera, 202, included under 67 orders, that have no indigenous species in the Canaries or Madeira. Many of these, about a quarter, being North Maroccan, i.e. only found in parts of Marocco farthest from the Canaries, would not be expected to occur in those islands, were it not that the vegetation of islands near to large continents often most resembles that of a higher latitude on the continent than that in which the islands are situated.
The following is a list of the Maroccan genera which are absent in Macaronesia;—those confined to North Marocco marked *; those which have been found in Macaronesia, but certainly introduced, marked ‖; those in italics have been discovered since our return from Marocco.[13]
| Clematis |
| Thalictrum |
| *Anemone |
| Aconitum |
| Berberis |
| Rœmeria |
| Corydalis |
| Cardamine |
| Morettia |
| Anastatica |
| Draba |
| *Erophila |
| Malcolmia |
| Diplotaxis |
| Moricandia |
| ‖Lepidium |
| Thlaspi |
| Iberis |
| Hutchinsia |
| Isatis |
| Ceratocnemum |
| *Cakile |
| *Hemicrambe |
| Cleome |
| Capparis |
| Caylusea |
| Fumana |
| Polygala |
| Velezia |
| Dianthus |
| Holosteum |
| Buffonia |
| Lœfflingia |
| Montia |
| Althæa |
| Malope |
| *Radiola |
| Peganum |
| Celastrus |
| Zizyphus |
| Acer |
| *Coriaria |
| Lotononis |
| Crotalaria |
| Argyrolobium |
| *Calycotome |
| Anthyllis |
| *Securigera |
| Coronilla |
| Colutea |
| *Glycyrhiza |
| Hedysarum |
| Ornithopus |
| Ebenus |
| *Pisum |
| Ceratonia |
| ‖Acacia |
| Saxifraga |
| Parnassia |
| Ribes |
| *Drosophyllum |
| *Peplis |
| *Ecbalium |
| *Hydrocotyle |
| Eryngium |
| Deverra |
| Hippomarathrum |
| Kundmannia |
| *Magydaris |
| Sclerosciadium |
| Meum |
| Heracleum |
| *Peucedanum |
| ‖*Coriandrum? |
| Thapsia |
| Elæoselinum |
| Gaillonia |
| Putoria |
| Callipeltis |
| Asperula |
| Crucianella |
| *Valeriana |
| ‖Centranthus |
| *Fedia |
| Nidorella |
| Nolletia |
| Micropus |
| Leysera |
| Grantia |
| Anvillea |
| *‖Xanthium |
| Achillea |
| Cladanthus |
| Echinops |
| Xeranthemum |
| Onopordon |
| Stæhelina |
| Crupina |
| *Leuzea |
| Carduncellus |
| Catananche |
| Hyoseris |
| Phœcasium |
| Hieracium |
| Scorzonera |
| Jasione |
| Trachelium |
| *Calluna |
| Armeria |
| Limoniastrum |
| Plumbago |
| Coris |
| Argania |
| Fraxinus |
| Phyllyrea |
| *Vinca |
| Nerium |
| Dæmia |
| Glossonema |
| Boucerosia |
| *Microcala |
| Cicendia |
| Trichodesma |
| Echinospermum |
| Rochelia |
| Nonnea |
| Cerinthe |
| Calystegia |
| *Mandragora |
| Anarrhinum |
| *Pinguicula |
| ‖*Acanthus |
| Vitex |
| Lycopus |
| *Satureja |
| Hyssopus |
| Cleonia |
| Zizyphora |
| *Betonica |
| Ballota |
| Boerhavia |
| Corrigiola |
| Scleranthus |
| Sclerocephalus |
| Polycnemum |
| Telephium |
| *Obione |
| Salicornia |
| Caroxylon |
| Passerina |
| Osyris |
| Andrachne |
| *Ulmus? |
| Celtis |
| Quercus |
| Populus |
| Ceratophyllum |
| Callitris |
| Cedrus |
| Aceras |
| *Serapias |
| *Cephalanthera |
| *Crocus |
| Leucojum |
| *Lapiedra |
| *Tapeinanthus |
| *Corbularia |
| Narcissus |
| Aurelia |
| *Alisma |
| Damasonium |
| *Triglochin |
| Chamærops |
| Gagea |
| *Hyacinthus |
| Anthericum |
| *Simethis |
| *Aphyllanthes |
| Colchicum |
| Erythrostictus |
| *Convallaria |
| *Schœnus |
| *Leersia |
| Lygeum |
| *Crypsis |
| *Alopecurus |
| Macrochloa |
| *Sporobolus |
| Ammophila |
| ‖Arundo |
| *Ampelodesmos |
| Phragmites |
| Pappophorum |
| Echinaria |
| *Spartina |
| *Airopsis |
| Gaudinia |
| Glyceria |
| Secale |
| Elymus |
| *Lepturus |
| Anthistiria |
These 202 genera, which are absent in the Canaries, comprise upwards of 300 Maroccan species, including Eryngium, with eleven species, Coronilla with eight, Diplotaxis with seven, Narcissus, Anthyllis, Polygala, Passerina, and Quercus five each, besides twenty other genera with three or four each. Not a few of them contain very common and wide-spread species, as do all the above-named, as well as Clematis, Malcolmia, Cardamine, Dianthus, Hedysarum, Heracleum, Asperula, Achillea, Onopordon, Hyoseris, Scorzonera, Phyllyrea, Fraxinus, Calystegia, Anarrhinum, Ballota, Populus, Chamærops. That no species of these or of many of the other genera should exist in the Canaries is inexplicable, considering the position and extent of the Archipelago, and the means of migration which must exist between it and the mainland.
The species common to Macaronesia and Marocco exclusively, are in so far as is at present known:—
| Helianthemum canariense, Jacq. | Sonchus acidus, Schousb. (In Lancerotte, only a single plant, possibly introduced) |
| Polycarpia nivea, Ait. (also occurs in C. de Verde) | Lithospermum microspermum, Boiss. |
| Zygophyllum Fontanesii, Webb | Linaria sagittata, Poir. |
| ?Cytisus albidus, DC. | Chenolea canariensis, Moq. |
| Ononis angustissima, Lam. (?A form of 0. Natrix) | Salix canariensis, Chr. Sm. (rather uncertain) |
| Astragalus Solandri, Lowe (Madeira only) | Romulea grandiscapa, Webb. (Perhaps only a var., but Baker keeps it) |
| Astydamia canariensis, DC. | Asparagus scoparius, Lowe. (Not quite certain) |
| Bowlesia oppositifolia | |
| Odontospermum odorum, Schousb. |
Although it would be out of place here to discuss all the questions raised by this slight sketch of the peculiarities of the Canarian Flora, there are some of them which so intimately bear upon the Maroccan as to awaken attention.
The wonderful development in the Canaries of endemic species belonging for the most part to Mediterranean types, points to the very early introduction of the parent forms of these, and the long isolation both of the Archipelago and its separate islets. It is in accordance with generally accepted views, to assume that the endemic species of each genus have been derived from parent forms originally introduced into one or more of the islets; and that as the descendants of these species spread over the Archipelago they were exposed to different conditions in each islet, resulting in their varying, and in the segregation and conservation of different local varieties each in its own insular birth-place; a supposition which is in accordance with the fact that those endemic species are really very local, many being confined to a single islet. In Marocco the parent forms of its Flora would be exposed to no such diverse conditions, and the areas in which varieties occurred, not being isolated, would be exposed both to invasion on all sides by other plants, and to destruction by agencies that affected the whole surrounding country, as drought, floods, insects, and birds.
The tropical types in the Canaries, with the exception of the Egypto-Arabian and the trees mentioned under V. c., are chiefly weeds of wide distribution, which have not reached Marocco, because of its want of ports and its limited commerce.
Finally the Dracæna, together with the tropical trees of Myrsineæ, Sapotaceæ (in Madeira), and Laurineæ, and the Egypto-Arabian types, suggest the hypothesis that at a very remote period these and many other plants of warmer and damper regions flourished in the area included in North-West Africa and its adjacent islands, and that they have been expelled from the continent by altered conditions of climate, but have been preserved in the more equable climate and more protected area of the Atlantic Islands.
Ball, who has given me valuable aid on many points discussed in this article, directs my attention to the important differences that exist between the vegetation of the eastern group of the Canary Islands—Fuertaventura, Lanzarote, and the adjacent islets—the ‘Purpurariæ’ of authors, and the western group, including Teneriffe, Grand Canary, &c.
In the first place, nearly all the characteristic Canarian types are absent in the eastern group. Out of fifty-four genera above enumerated as present in the Canaries but wanting in Marocco, two are in the Canaries confined to the eastern islands: one of these, Traganum, is an African desert type, probably to be found in South Marocco; the other, Melianthus, a Southern African plant, and scarcely indigenous. Of the remainder Plocama alone is certainly present, and three other generic types probably exist in that group; while forty-eight genera, including eight out of nine peculiar to the Canaries, are apparently absent. In the next place several characteristic desert plants, such as Oligomeris subulata, Ononis vaginalis, Convolvulus Hystrix, and Traganum nudatum, are present in the ‘Purpurariæ,’ but absent from the western islands.
Although the Flora of the Purpurariæ is incompletely known, and our acquaintance with that of the neighbouring African coast between the rivers Sous and Draha is extremely imperfect, these facts tend to prove that there is a closer botanical relationship between the eastern islands and the adjoining continent than there is between them and the western portion of the Canarian Archipelago. Such relationship might be brought about in three different ways.
1. The greater dryness and heat of the eastern islands may have favoured the immigration of African forms, and at the same time led to the destruction, or weeding out, of the characteristic Canarian types. In this case the cause would be of a purely local and climatic character.
2. We may believe in the trans-oceanic migration of some African species to the nearer islands, along with the transport of some Canarian species (those enumerated in p. 416, and others which may be hereafter found) to the neighbouring continent.
3. An ancient extension of the continent to the Purpurariæ, leaving the other islands separated by deep sea.
It is an objection to the latter hypothesis that a profoundly deep ocean bed lies between the lines of 100 fathom soundings that girdle the islands and the African coast respectively; and that while the 100 fathom line extends about thirty miles from the coast of the continent, it is never more than five miles, rarely more than one or two, from those of the islands.
In favour of the hypothesis of trans-oceanic transport it may be remarked that the distance between the African coast and Fuertaventura is not more than seventy miles, and that a moderate change of level of about 600 feet would reduce that distance by one-half, while it would but slightly affect the interval that separates the Purpurariæ from the other islands.
Among the possible causes leading to an interchange of species between the Purpurariæ and the African coast the agency of man must not be omitted. The fishermen of those islands were formerly in the habit of visiting some points on the opposite coast, although intercourse of this kind has almost ceased in recent times.
It must be observed that our knowledge of the vegetation of the Canary Islands is yet incomplete. Although several additions to the Flora have been published by C. Bolle and others, no supplement to Webb’s ‘Phytographia’ has been published. Several additional species exist in herbaria, besides those that may be hereafter found.
So little is known of the geology of Marocco, that there are no data for ascertaining whether during antecedent geological periods it contained a more tropical Flora than now; but evidence in support of such a hypothesis is forthcoming in Madeira, where fossiliferous beds which have been referred to ‘some part of the Pliocene period’[14] have been discovered, containing leaves referable in part to existing species of Madeiran plants, and in part to extinct ones of tropical aspect;[15] and it is well ascertained that during preceding geological periods Western Europe was clothed with a vegetation that suggests a very much warmer climate than now prevails, and of which vegetation the Laurus nobilis in the south-west of the continent has been supposed to be a surviving representative.
In Grand Canary, also, Upper Miocene beds exist, containing numerous species of fossil shells, of which one is an Oregon species, and another tropical African; and in more recent deposits of the same Archipelago many shells have been found which no longer inhabit the adjacent seas, including tropical West African, Mozambique, and Mediterranean species.
We can form no conception of means of transport from the American continent that would transfer the parent species of Bowlesia and of the Bystropogons from the Andes to the Atlantic islands; and we can but hazard the assumption that, at some very distant date, these genera existed in more eastern parts of America, from whence seeds were transported across the ocean. On the other hand, the transport of parent forms or existing species from the continents of Europe and Africa to the Atlantic islands may have been much facilitated by greater extensions of land in bygone ages. Madeira, the Canaries, and the Cape de Verde Islands, are all supposed to stand on a submarine platform which skirts the coasts of Western Europe and North-Western Africa, and whose submerged margin immediately to the westward of the position of the islands descends rapidly to a profound depth. The westward margin of this platform was possibly the coast-line in Miocene times. An elevation of its surface of a few hundred feet would approximate the islands to the mainland very materially, and greatly facilitate transport. That they were, however, ever united to the continent is opposed to the views of most competent geologists. Lyell, speaking of this, says: ‘The general abruptness of the cliffs of all the Atlantic islands, coupled with the rapid deepening of the sea outside the 100 fathom line, are characters which favour the opinion that each island was formed separately by igneous eruptions, and in a sea of great depth.’ Moreover, the Azores, whose botany in so many respects resembles that of the other Atlantic islands, as distinguished from that of the continent, are enormously more distant from the mainland; and these islands stand on a platform of their own, separated from the continental one by an ocean of profound depth; so that any theory of transport which applies to the Canarian and Madeiran Archipelagos, should apply also to the Azorean.
It remains a point of some nicety to decide whether the Macaronesian islands should be regarded as a Botanical province apart from the Mediterranean, or a sub-division of the latter. The assemblage of American and Oriental genera which their Flora contains, together with the arboreous representatives of tropical Laurineæ, all so entirely foreign to the European Flora, would give it a title to be called a Botanical province; and to this as a further title is the prevalence of a considerable proportion of North European plants, in the Northern Archipelago especially. On the other hand, fully two-thirds of the species are typical of the Mediterranean Flora, and by far the majority of the remainder are derivative species of the same origin; so that, on the whole, I am disposed to regard it as a very distinct sub-division of the Mediterranean province, which owes its peculiarities partly to the conservation of types once common to West Europe and North Africa, but which have been eliminated in those regions, and partly to the effect of isolation and climate on the progeny of species still existing in those regions.