66 THE BIOGEOGRAPHY OF ISLAND LIFE
Table 3.2Native higher plant species richness and endemism of
selected islands or archipelagos. (From Groombridge 1992; Davis
et al. 1995, Sziemer 2000, Izquierdo et al. 2004, Traveset and
Santamaría 2004, Arechavaleta et al. 2005.) These figures should be
treated cautiously as different values for some islands can be found,
in cases even within a single publication (see Groombridge 1992,
Tables 8.3, and 14.1)
Island or Number of Number of % Endemic
archipelago species endemic species
Borneo 20 000–25 000 6000–7500 30
New Guinea 15 000–20 000 10 500–16 000 70–80
Madagascar 8000–10 000 5000–8000 68.4
Cuba 6514 3229 49.6
Japan 5372 2000 37.2
Jamaica 3308 906 27.4
New Caledonia 3094 2480 80.2
New Zealand 2371 1942 81.9
Seychelles 1640 250 15.2
Fiji 1628 812 49.9
Balearic 1359 89 6.5
Canaries 1300 570 44.3
Hawaii 1180 906 89.8
Mascarenes 878 329 37.5
Madeira 793 118 14.9
Galápagos 529 211 39.9
Cook Islands 284 3 1.1
Cape Verde 224 66 29.4
Azores 197 67 34.0
St Helena 74 59 79.7
New Guinea is taken as the world’s largest,
islands constitute about 3% of the land surface
area of the world. The small selection of 20 islands
and archipelagos in Table 3.2 provides a minimum
estimate of about 35 500 species endemic to those
same islands, amounting to some 13.5% of the
world’s higher plant species, indeed, just 10 of
these islands/archipelagos account for 12.8%. It
has been calculated that the Pacific islands contain
about 22 000 vascular plant species, nearly half of
which may have been introduced by humans. Of
the 11 000–12 000 native species, about 7000 are
considered to be endemic, most being found
within a single island or island archipelago (Davis
et al. 1995).
All such figures come with large error margins.
Indeed, estimates of the number of flowering
plant species in the world have varied between
240 000 and 750 000 (Groombridge 1992, p. 65).
However, island species are as much a part of
these uncertainties as are continental species (see
data for New Guinea and Borneo, Table 3.2), so the
relative importance of island species is unlikely to
be seriously diminished by further refinements of
the estimates. It is a reasonable estimate that about
one in six of the Earth’s plant species grows on
islands, and one in three of all known threatened
plants are island forms (Groombridge 1992,
p. 244). Clearly, in terms of plant biodiversity, the
islands of the world make a disproportionate
contribution for their land area and are also suf-
fering further disproportionate pressure in terms
of the maintenance of that biodiversity.
The percentage of endemics varies greatly among
islands. The highest proportions are often associ-
ated with ancient continental islands, such as
Madagascar and New Zealand. Large numbers of
endemics are also associated with the larger, higher
oceanic islands in tropical and warm-temperate
latitudes. Hawaii, to provide a classic example, has
about 1180 native vascular plants, and of the 1000
angiosperms (flowering plants) about 90% are
considered endemic (Wagner and Funk 1995). A
more conservative estimate for their numbers is 850
endemic species, although the figure could conceiv-
ably be as high as 1000 (Groombridge 1992; Davis
et al. 1995). Some lineages have radiated spectacu-
larly. The silversword alliance comprises 28
endemic species, apparently of monophyletic ori-
gin (i.e. a single common ancestor), but placed in
three genera: Argyroxiphium, Dubautia, and Wilkesia
(Wagner and Funk 1995). The genus Cyrtandra
(Gesneriaceae) is represented by over 100 species,
and although they may not be monophyletic, their
radiation is no less impressive (Otte 1989; Wagner
and Funk 1995). The Macaronesian flora provides
the best developed Atlantic equivalent to Hawaii,
with some exquisite examples of largely mono-
phyletic radiations. For instance, there are more
than 60 monophyletic endemic species of
Crassulaceae, distributed across the genera
Aeonium,Greenovia,Aichryson, and Monanthes; there
are more than 20 species representing mono-
phyletic taxa within 4 genera of Asteraceae, namely