The Botany of Iceland - 01.12.1942, Blaðsíða 16

242
M. P. CHRISTIANSEN
out, will there be a possibility of obtaining an accurate picture of the
distribution of the genus Taraxacum in the North Atlantic flora.
What the result of this investigation will be, it is not possible to
say exactly; my experience, however, seems to show that in isolated
areas there will occur many endemic species.
6. Endemic Species and Determination of Species.
Of the 116 Taraxacum-species recorded in Iceland, 90 have so far
been found in this country only. It is a large number, and several of
the species concerned may also occur in other places in the North
Atlantic area, if this, as suggested above, is more thoroughly explored.
However, it is possible that Iceland has, in fact, rather a large number
of endemic Taraxacum-spedes. Mr. Thorv. Sörensen has
proved experimentally, for some Danish Taraxacum-species, that they
are able, though to a slight extent only, to form new, vital, and constant
species. So as far as the matter has been investigated, it seems likely
that Icelandic Taraxacum-spedes, being apogamous like the Danish
ones, will also be able to form new, constant species, which, on ac-
count of the isolated position of the country, have only with difficulty
been able to spread to other countries; and this furnishes a plausible
explanation of the fact that about 4/5 of the Taraxacum-spedes in Ice-
land have not been found outside that country. Now, as assumed above,
renewed investigations of the North Atlantic area will no doubt show
that part of the species mentioned are more widely distributed than
is now known; but the number of endemic species will surely always
prove to be large. This would agree with the facts found for other
plant-genera with apogamous species. Here one example will suffice.
C. H. Ostenfeld and Johs. Gröntved: ‘The Flora of Ice-
land and the Faeroes’, mentions 57 Hieracium-spedes or -forms from
Iceland and 22 from the Faeroes; but none of these species or forms
are common to the two floras. The case of the Taraxacum-species is
not quite so remarkable, and the explanation surely is that many
Taraxacum-species are strongly influenced by cultivation, and thus
have larger possibilities for spreading than species of the genus Hiera-
cium. Of the Taraxacum-spedes in Iceland it is indeed precisely those
that have been favoured by cultivation which are widely distributed.
Further the result of T h o r v. S ö r e n s e n’s investigations is some-
what alarming. Does it not mean that the exploration of the genus
Taraxacum can never be brought to an end because new species will