Douglas, Inflorescence development in Carnarvonia 
771 
Phylogenetic affinities 
The inflorescence architectures of different proteaceous taxa are valuable in defining 
taxonomic groups and specific architectures appear to be generically conserved in 
most cases. Proteaceous taxa with compound racemiform inflorescences plus variable 
flower numbers on ascending branches include Symphionema and Conospermum of 
Proteoideae. The developmental events leading to the inflorescence of Carnarvonia 
are valuable in understanding the evolution of reproductive structures in Proteaceae. 
It can be hypothesized that the inflorescence structure in Carnarvonia is a novel state 
derived from the single-flowered condition found in the inflorescences of Proteoideae, 
Persoonioideae and Sphalmioideae compared to the two-flowered condition in 
Grevilleoideae. In all single-flowered systems, the flower develops as a product of 
the axillary meristem and no prophylls are present (Douglas 1994, unpub.; Douglas 
& Tucker 1996a,b, in press). In fact, the first two tepals to be initiated are in transverse 
positions analagous to the a- and [i-phyll sites. In Grevilleoideae, an axillary meristem 
enlarges in the axil of a common bract on the main axis. The meristem becomes 
transversely oblate and two floral bracts are initiated, one on each side. Within the 
axil of each of the floral bracts, a floral meristem will enlarge (the pattern of tepal 
initiation being identical to flowers of the other subfamilies) and the apical residuum 
of the short-shoot axis differentiates and senesces. There is no differential elongation 
of subtending internodes between the two flowers and likewise there are no terminal 
flowers in Grevilleoideae examined (Douglas 1994; Douglas & Tucker, 1996a). It has 
been hypothesized that the flower-pairs in Grevilleoideae are either the product of 
reduction of secondary inflorescence branches to two flowers or the product of a 
constrained amplification of first-order axillary meristems to two flowers (Douglas 
& Tucker 1996a). 
Carnarvonia is the sister taxon to Grevilleoideae in Johnson & Briggs's (1975) 
phylogeny. Carnarvonia was excluded from Grevilleoideae based on several features 
including the fact that the inflorescence of Carnarvonia does not have the flower-pair 
condition (Johnson & Briggs 1975). As the sister-taxon to Grevilleoideae, there is an 
implied morphological transformation hypothesis of reduction to the flower-pair 
condition from a Carnarz>onia-\ike inflorescence architecture and/or the diversification 
of inflorescence architecture from a similar developmental program in each lineage, 
one branch leading to Cariiarvonia the other to Grevilleoideae. To attain the flower- 
pair condition from a Carnarvonia inflorescence there could be a change in 
developmental timing and growth between the initiation of the first two metamers 
of a subunit and a loss of the ability of the terminal portion of a subunit meristem 
to develop into a flower. The fact that in Carnarvonia there is differential enlargement 
of axes, and the presence of a terminal flower on each subunit, the first tepal of 
which is initiated in a site consistent with the phyllotactic pattern of the subunit 
before moving to a 1/4 pattern suggests that the inflorescence form is possibly 
derived from a single-flowered system as has been hypothesized for Grevilleoideae 
(Johnson & Briggs 1975; Douglas & Tucker 1996a). 
Venkata Rao (1971) and Engler (1889) classified Carnarvonia as a member of 
Grevilleoideae. Under this hypothesis, the Carnarvonia inflorescence would be derived 
from amplification of the flower paired condition. Developmentally, this 
transformation could result from an amplification of the primary axillary meristems, 
perhaps a proliferation of the axillary meristem via a delay in the commitment of 
flowering and the production of terminal flowers on each subunit, the latter of 
which is unique in the family. Morphologically, the hypothesis that Carnarvonia is 
derived from within Grevilleoideae seems unlikely given the synorganised floral 
