238 
G.J. Keighery, N. Gibson, K.F. Kenneally, A.A. Mitchell 
Figure 1 Map of Koolan Island,showing major vegetation types and location of town, airstrip and mine. 
and access limitations. Voucher collections were 
made of all fertile plants found and notes made on 
their distribution and abundance. While detailed 
searches were undertaken for naturalised weed 
taxa, due to time limitations no attempt was made 
to record all exotic taxa found in the townsite. 
Vouchers were lodged in PERTH. Nomenclature 
largely follows Wheeler et al. (1992). Additional 
records were available from previous visits by KFK 
and AAM as well as other collections lodged in 
PERTH. 
A structural vegetation map was compiled from 
field notes and a 1: 30 000 colour mosaic based on 
August 1992 photography (Figure 1). 
RESULTS AND DISCUSSION 
Flora 
Two hundred and eighty-two taxa (species, 
subspecies and varieties) were recorded from 79 
families. Forty-three of these were exotic taxa from 
19 different families; three of these families 
(Moringaceae, Solanaceae and Tumeraceae) were 
only represented by introduced taxa. The most 
well represented families were the Poaceae (22 
native, 11 naturalised taxa), Papilionaceae (15 
native, 5 naturalised taxa), Euphorbiaceae (15 
native, 3 naturalised taxa), and Myrtaceae (11 
native taxa) (Appendix 1). Species composition 
clearly shows the tropical nature of the flora with 
high proportions of grasses and Euphorbiaceae. It 
is, however, a sub-humid tropical flora sharing 
only 12% of the evergreen tropical flora of 
Christmas Island (Gentilli 1972, Du Puy 1993). 
Approximately half of the species co-occurring 
between the two islands are pan-tropical weeds. 
Koolan Island falls on the western margin of the 
Fitzgerald Botanical District which covers some 
83,330 km 2 (Beard 1979). The flora of this area is 
still poorly known. Hnatiuk (1990) recorded 842 
taxa from this region while the recently completed 
Kimberley Flora (Wheeler et al. 1992) record 1030 
taxa. The present survey has added a further 24 
taxa. Thus, 27 % of the flora of the entire Fitzgerald 
Botanical District has been recorded on Koolan 
Island although the island represents less than 0.1% 
of the land area of this District. 
Weeds 
Several weed taxa were largely restricted to the 
six steep gullies north and south of the townsite 
down which the treated sewage was discharged 
(Figure 2). In particular Euphorbia cyathophora and 
Clitoria ternatea were common and locally 
dominant in the bottoms of these gullies. In Creeks 
1 and 2 on the north side of the settlement Senna 
alata, a garden escape, has become wide spread, 
reaching heights of 4 m. This is the first record of 
this species naturalised in Western Australia. It is 
also naturalised in the Darwin area. Another 
garden escape which has become widespread along 
the road verges and in the creeks is Turnera 
