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Telopea Vol. 6(4): 1996 
by only one Cladocerapis species if Moldenke's predictions extend beyond the Californian 
flora. Instead, collections indicated that there was no obvious domination of a Persoouia 
species by one of each of the three Cladocerapis species. Pollen load analyses indicated 
that some members of all three Cladocerapis species continued interspecific foraging on 
Persoonia at Hilltop. Perhaps resource partitioning by bees can occur only if floral 
diversity and density increases while bee diversity and density remains constant. 
We may confirm then that the high frequency of FI hybrids recorded between 
Persoonia species in eastern Australia is based on the general weakness of all pre- 
zygotic barriers associated with interspecific isolation. Persoonia species in eastern 
Australia are often sympatric and floral phenology shows a broad overlap. The mere 
presence of first generation hybrids indicates that some parent species are 
intercompatible. Different suites of floral characters in Persoonia such as floral tube 
length, anther colour and differing scents do not visibly discourage interspecific 
foraging by the four to five taxa of major pollinators. 
At the Hilltop site the same three Leioproctus (Cladocerapis) species were collected on 
each of the three, co-blooming Persoonia species. At Nerriga, the most common pollinator, 
L. incanescens, was collected on co-blooming P. inicrophplla and P. mollis. When native 
poUinators fail to discriminate between the flowers of shrubs in the same genus recurrent 
hybridisation cannot be blamed exclusively on the naturalised A. /nellifera. 
When Persoonia species are sympatric and have overlapping flowering periods, up 
to 28% of their primary pollinators make interspecific foraging bouts. This helps to 
explain the high frequency of FI hybrids in Persoonia in eastern Australia. In some 
other angiosperm genera (e.g. Iris, Phlox, Opuntia, Qiiercus) the comparative lack of 
interspecific isolation has encouraged introgression or microspeciation (see review 
in Futuyma 1986). The comparative lack of autoploidy and backcrossing between 
parents and first generation hybrids in Persoonia suggests that postzygotic barriers 
(c^. FI sterility or poor survival rate) may be more important in the maintenance of 
interspecific isolation in this genus. 
Under these circumstances the genus Persoonia in eastern Australia may represent 
a species flock (sensu Mayr 1963). This section of the genus would have radiated 
rapidly during the Tertiary (Weston 1981, Truswell 1990). With the retreat of 
rainforests and moist Nothofagus forests, Persoonia might have undergone rapid 
speciation within the expanding and fragmenting shrublands and eucalypt forests 
(Truswell 1990). Just as the diversification of the orchid genus, Thelymitra, is 
identified by the key innovation of fusion of the column wings above and behind 
the fertile anther (Burns-Balogh & Bernhardt 1988; Bernhardt 1993), diversification 
within Persoonia may have depended, in part, on the evolution of basally hinged 
tepals forming a nectar chamber under the stalked ovary. 
The Persoonioideae lack such derived reproductive features as the massive 
inflorescence, protostigma, biporate pollen grain, reinforced-wiry styles, zygomorphic 
nectary found elsewhere in the family. It is tempting to speculate that insect- 
pollination is ancestral to the Proteaceae with vertebrate pollination secondarily 
derived. This recurrent trend in floral evolution has been proposed repeatedly for 
other families including the Polemoniaceae (Grant and Grant 1965), Fabaceae sens, 
lat. (Arroyo 1981) and the Orchidaceae (Dressier 1981). 
Of course, this hypothesis must be treated with considerable caution. Persoonia 
pollination does not follow the patterns of generalist entomophily described, for 
example, in the relictual magnolioids and their allies. In these families pollination is 
achieved by the much broader exploitation of a wide range of insects in different 
Orders (Hymenoptera, Coleoptera, Lepidoptera, Thysanoptera, Diptera). These insects 
have small bodies and often lack forelegs modified to manipulate anthers (Barth 
