The Geography of Phytochemical Races

250 6 Oceanic Islands
levels of species endemism (for such a limited land area) anywhere in the world.
According to Wagner et al. (1990, 1999), writing in the Manual of the Flowering
Plants of Hawaii, there are 32 endemic genera (31 dicot, 1 monocot), accounting
for 15% of island genera, 850 endemic species (89%), and 1094 endemic taxa overall
(91%). From a slightly different perspective, there is 94% endemism in dicot
taxa and 73% in monocot taxa. The fl ora consists of 146 families (none endemic),
649 genera, and 1817 species. Fosberg (1948) estimated that the affi nities of the
Hawaiian fl ora were 40.1% Indo-Pacifi c, 16.5% Austral, 18.3% American, 12.5%
Pantropical, 2.6% Boreal, and 10.3% obscure.
Three major contributions dealing with the Hawaiian fl ora have appeared in
recent years to which the interested reader is referred for detailed descriptions of the
fl ora and discussions of evolutionary relationships. The two volume fl ora by Wagner
et al. (1990, 1999) was referred to above. Volume 1 includes a long introduction that
deals with many aspects of the islands, including geology, climate, and vegetation.
Hawaiian Biogeography: Evolution on a Hot Spot Archipelago, edited by Wagner
and Funk (1995), provides detailed summaries of relationships and evolutionary
history of several of the major groups of vascular plants on the islands. This volume
also features an up-to-date treatment of the islands’ geology. The third is a book
dealing specifi cally with the silversword alliance (Argyroxiphium, Dubautia, and
Wilkesia) edited by Carlquist et al. (2003).
The Hawaiian archipelago can be thought of as consisting of two groups of
islands, the high islands that comprise the “tourist group,” and a series of lesser
islands extending roughly northwestward from Kauai. The islands have resulted
from the movement of the Pacifi c Plate over a “hot spot” located at approximately
19°N, 155° 30′W (Clague and Dalrymple, 1987). The main group of islands
(maximum estimated ages in parentheses in millions of years) consists of Hawaii
Island (0.43); Maui (1.32); Kahoolawe (1.03); Lanai (1.28); Molokai (1.9); Oahu
(3.7); Niihau (4.89); and Kauai (5.1) (Carson and Clague, 1995). The complex consisting
of Maui, Kahoolawe, Lanai, and Molokai is frequently referred to as “Maui
Nui,” or big Maui, since these four formed a single landmass during Pleistocene
glaciation. Hawaii Island (known locally as the Big Island) is actively volcanic;
volcanoes on the other islands range from dormant to extinct awaii. Beyond Kauai,
the oldest of the extant tall islands, lies a chain of degraded volcanic islands (e.g.,
Nihoa, Necker, Gardner Pinnacles, Laysan, and Lisianski) and reefs stretching
over 3000 km to Midway Island (28°12′N, 177°24′W). Beyond Midway lies
the Emperor Chain, a series of seamounts that extends some 2400 km in a more
northerly direction from the Daikakuji Seamount to Meiji Seamount (Carson and
Clague, 1995).
A closer look at the age of the Hawaiian Islands is useful. In attempting to estimate
the time of arrival of propagules on the islands, it is important to realize that there
have been receptive high islands for a much longer time than is indicated by the age
of Kauai (ca. 5.1 million). As Clague and Dalrymple (1987) point out, the Leeward
Islands range from about 7 to 28 million years old. Attempts to address the age of
arrival of a propagule and rate of subsequent genetic divergence of new species