Journal of the Royal Society of Western Australia, 86(1), March 2003 
Forty volunteers took part in the earlier collecting 
sessions and a total of approximately 500 person hours 
was spent in collecting specimens. The surveys were 
intended to cover as much of the island as was feasible in 
the time available. There was no formal grid survey 
pattern established nor were quadrats or transects 
included in the survey. All previously listed species were 
targeted, and recorded source areas were searched. At 
the time of collecting, details of each plant and its 
provisional identification, habitat, and locality were 
noted. Latitude and longitude were estimated from a 
photocopied aerial photograph on which a grid had been 
superimposed. The soil type and the nature of the 
vegetation in which the collected plant was growing 
were also recorded. 
Each collection consisted of two specimens, one of 
which was submitted to the WA Herbarium for 
identification. These specimens were retained, apart from 
those of cultivated species that had not become 
naturalised. The Rottnest Regional Herbarium retained 
the duplicate specimens of all species collected. Where 
the size of the specimens made collection impracticable 
(e.g. palm trees) photographs were used. This collection, 
including photographs, is lodged with the Rottnest 
Island Authority. A colour photocopy was taken of one 
pressed specimen (or photograph) for each species in the 
collection and these are held by the Rottnest Island 
Authority for public reference. 
We compiled a comprehensive list with current 
nomenclature of all species recorded for Rottnest Island, 
and attempted to reconcile it with all previous floristic 
lists. Our list included cultivated species that had become 
naturalised. We use the term 'naturalised' in a broad 
sense to include species in the colonisation phase that are 
starting to multiply on Rottnest without human 
intervention, and those in the naturalisation phase that 
have reproduced for several generations (Groves 1986). 
Nomenclature was based on the WA Herbarium 
identifications of the specimens collected in the recent 
su PP° rted b Y det *ils in Paczkowska & Chapman 
2000) or occasionally 'FloraBase' (Western Australian 
Herbarium, http://www.calm.wa.gov.au/science/ 
Horabase html) and, in the case of some exotic taxa, by 
Bodkin (1993). Authors were not included but are 
available from the above references. Common names are 
taken from Paczkowska & Chapman (2000), and for 
orchids from Hoffman & Brown (1992). A second list was 
compiled for deleted names, annotated with reasons for 
heir deletion from the Rottnest list or change in 
taxonomic status. Another list was compiled for species 
a had been cultivated outside gardens but had not 
become naturalised. These species are of historical and 
aesthetic importance on the island, and some may 
naturalise in the future. 
i qJ iccoo S ^‘ eS between ‘he two censuses (late 
1950s, and 1998-2001) was investigated. It is difficult tc 
assess turnover, because of the problems of measuring 
actual immigration and extinction rates, as noted b 
rannnf L 69) ^ Abb0tt < 1983 )' beCau ^ collection: 
cannot be considered complete. Nilsson & Nilsson (1985 
census efficiency and turnover when recording 
vascular plants on islands, and concluded that efficiency 
correlates positively with the time spent in taking th, 
census, and negatively with island area. Ever 
standardised searches by professional botanists recorded 
only 79% of the best estimate and the authors concluded 
that at most only 1% of the vascular plant species present 
on an island becomes extinct annually (Nilsson & Nilssoi\ 
1985). Whittaker (1998) noted that most turnover studies 
are in fact merely rates of changes in lists (as is this 
survey), and that turnover figures can be distorted by 
'crypto-turnover' (exclusion of species that botl\ 
immigrated and became extinct between surveys), and 
'pseudo-turnover' (incomplete censuses). 
Nevertheless, an assessment is made here using th^ 
available information. Turnover is taken as a combined 
effect of species 'extinction' and 'immigration'. A species 
was listed as extinct if it had been recorded previously, 
but was not listed in the latest census. Similarly the terrr\ 
'immigrated' is applied to species recorded in the recent 
survey, but not previously. Turnover, immigration and 
extinction rates are calculated as suggested by Abbott 
(1977) and Abbott & Black (1980); rate of turnover =* 
200(I+E)/[ (S, +S 2 ). (t 2 - t,)]; extinction rate = 200 (E)/[(S 
+S 2 ) (t 2 - tj)]; and immigration rate = 200 (I)/[(S 1 +S 2 ) . (t 2 
- t t )]; where E is the number of species that wer^ 
presumed extinct, I is the number of species that 
immigrated, (S t + S 2 ) is the sum of the number of species 
recorded at the two censuses, and (t 2 - t x ) is the tims 
elapsed between the two censuses. For the purposes of 
this survey, we assumed that 42 years elapsed (t t = 1958 
and t 2 = 2000). 
Some nomenclatural problems could not be resolved 
with certainty and these are addressed under 'taxonomic 
issues' in Appendix 1. 
Results 
A total of 196 vascular plant species was recorded for 
Rottnest Island between 1998 and 2001 (Table 1). The 
majority, 113 (58% of the total), were native species and 
83 (42%) were introduced. The total comprised the 184 
species collected for the RRH, five species recorded by 
other researchers since 1980 (Avellinia michelii, Cerastium 
glomeratum, Droscra ramellosa, Oxalis pes-caprac and Ruppia 
tuberosa), one seagrass ( Heterozostera tasmanica) and six 
orchid species ( Eriochilus dilatatus, Leporella fimbriata , 
Microtis media , Prasophyllum giganteum, Pterostylis aspera 
and Pterostylis sanguined). Nine seagrass and eight orchid 
species are known for Rottnest (D I Walker, School of 
Plant Biology, University of Western Australia, personal 
communication; A Brown, Science and Information 
Branch, WA Dept of Conservation and Land 
Management, personal communication); only eight 
seagrasses and two orchids were collected for the RRH. 
Seagrasses and orchids can be difficult to collect, and 
were under-represented in both the RRH collection and 
Storr's (1962) census of Rottnest Island flora in the 1950s. 
The comparable total number of species on the island 
in the late 1950s was 201 of which 124 (62%) were native 
species and 77 (38%) were introduced. This total 
consisted of 180 species recorded by Storr (1962), and 7 
other species lodged with the WA Herbarium at the time 
of his survey ( Bromus madritensis, a second Comesperma 
species, Heliotropium curassavicum, Hydrocotyle 
blepharocarpa, Polypogon tenellus, Sarcocornia blackiana and 
Zygophyllum billardierei). Ricinus communis , Agave sisalana, 
Droscra ramellosa and Lobelia alata, which were known to 
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