The Botany of Iceland - 01.12.1930, Page 84

74
II. M0I.HOLM HANSEN
Subularia formation has been described above, the Itan. reptans for-
mation under the flói (p. 70). There seems, however, to be no little
difference between the environment of these two formations. The
Subularia formation is found where tlie motion of the water (tem-
porarily or continuallj'?) is so strong that it causes a shifting of the
bottom material, in the Ran. reptans forination it is less strong and
no shifting takes place. As the third link in the chain we have the
flói; here the water is stagnant and the bottom covered with mosses.
All three formations have but a small density of species and
practically the same species group speclrum, a liigh E percentage
and concentration in the central part of the spectrum. The biolo-
gical spectrum is of special interest. In the Subularia formation Th
are dominant, in the R. reptans formation H, and in the flói G.
Tlie Koenigia flag and the flag mo represent the flag ve-
getation proper. The circling results are tabulated in table 17 A, 3—7.
Nos. 3—5 sliow the composition of the vegetation on flag at
Björk in the south country. The dominant species are in the first
place Koenigia islandica and Sedum villosum. Further Agrostis alba
and Jnncus spp. abound, J. bufonius, J. trighimis, J. biglnmis, Tri-
glochin palustre, Polggonum viviparum, Equisetum arvense, Sagina
nodosa, Minuartia verna, Cerastium alpinum, C. cœspitosum, Des-
champsia atpina, Festuca ovina, and Luzula spicata. The table
gives more precise information as to the part played by the in-
dividual species and the variation from locality to locality. Spora-
dically a number of plants occur which mostly originate from the
surrounding formations, jaðar and mo.
Nos. 6—7 represent the ilag mo at Lækjamót in the north
country. The dominant species are practically the same here (though
Juncus bufonius was absent in the north country), and the individual
species occur with almost the same F.-percentage. An essential dif-
ference between the flag mo and the Koenigia flag is due to the
presence of a quantity of mo plants in the flag mo, thus especially
Thalictrum alpinum, Rumex acetosa, Poa alpina and P. glauca, Par-
nassia palustris, Armeria vulgaris, Carex capiltaris, Sitene acaulis and
several others. Another marked difference between the flag mo
and the Koenigia flag is the great number of little knolls found in
the former.
The individual species are differently distributed over the sur-
face, some species being associated with the clayey soil others with
the knolls. On the clayey soil the vegetation is open, and here we