NOTES 
The American Element in the Hawaiian Flora^ 
The geographic derivation of any flora is a 
matter of interest not only to taxonomists 
and phytogeographers but also to students 
of geology and geography and to those with 
a general intellectual curiosity as well. Reli- 
able speculation on such a subject often pro- 
vides useful keys to other related topics such 
as the geological history of an area, its paleo- 
ecology, the migrations of its peoples, and 
the phylogeny of special groups of plants. 
The floras of oceanic islands seem to be 
particularly stimulating to such speculations, 
and that of the Hawaiian Islands has had its 
full share of theories. Hillebrand, Brown, 
Campbell, Skottsberg, and Copeland are 
among those who have expressed opinions. 
The latest such expression that I know of was 
presented by me, two years ago (in E. C. 
Zimmerman’s Insects of Hawaii 1: 107-119, 
1948). The outstanding characteristic of this 
collection of opinions is its diversity. Hille- 
brand and Brown, especially, recognized a 
large element of American affinity. Later 
writers have rather minimized this. 
My own approach differed from that of 
most earlier writers in being an attempt to 
ascertain the number and derivation of the 
probable original successful colonists re- 
sponsible for the present indigenous Hawai- 
ian flora. The percentage of each element in 
the present flora was then determined on the 
basis of these original colonizations rather 
than of the total present flora. This, it was 
felt, would eliminate the disproportion intro- 
duced by such rapidly evolving groups as 
Cyrtandra, the Rubiaceae, the lobeliads, 
^Paper read at Seventh International Botanical Con- 
gress, Stockholm, Sweden, July, 1950. Manuscript 
received September 28, 1950. 
Metrosideros, etc. It is thought that there were 
about 407 such successful colonists. 
The percentages of the floristic elements 
in the vascular flora, recognized on this basis, 
are as follows: 
REGION 
PERCENTAGE 
Indo-Pacific 
42.7 
Austral 
12.2 
American . . 
16.2 
Boreal 
3.1 
Pantropic 
15.4 
Obscure 
10.5 
The figures for the seed plants and vascular 
cryptogams were originally published separ- 
ately, but are here combined. For the Ameri- 
can element the seed plant percentage is 18.3 
and that of the pteridophytes, 11.9. There 
were possibly a total of 69 original successful 
immigrants from America, of which 51 were 
seed plants and 18 pteridophytes. 
Now, let us look at some of the interesting 
features of this American element. 
Of the total of 69 possible American in- 
troductions, 40, or about 58 per cent, have 
changed very little since their arrival. Twenty- 
one are identical or only varietally distinct 
from their American relatives. Nineteen are 
closely related species. Of the other 42 per 
cent, 19 species are clearly, though not 
closely, related to American plants; the re- 
maining 10 may be regarded as questionable. 
I am on insecure ground when discussing 
certain of the larger fern genera where the 
Hawaiian species may be closer to American 
ones than I realize. 
Of the total American component, only 
four genera, Isodendrion, Nothocestrum, Psycho- 
tria, and Hesperomannia, have given rise to 
any significant number of evolutionary off- 
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