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Seedling characteristics in the Casuarinaceae 
Robin Hwang and John G. Conran 
Abstract 
Hwang, Robin ! and Conran, John G. 2 ’ 3 (IResearch Division, National Museum of Natural Science, 
Taichung, Taiwan; 2 Department of Environmental Biology, The University of Adelaide, SA, Australia 5005; 
3 author for correspondence) 2000. Seedling characteristics in the Casuarinaceae. Telopea 8(4): 429-439. 
Seedling characters and their distributions within the genera of the Casuarinaceae and their 
sections are described for 45 taxa in the family representing three of the four genera and all 14 of 
the currently recognised sections in Allocasuarina. The cotyledons in Gymnostoma are petiolate, a 
feature absent from the other taxa examined. There were no obvious genus-level seedling features 
distinguishing either Casuarina or Allocasuarina, although red-purple cotyledons at senescence are 
common in Casuarina but rare in Allocasuarina. Several features are informative at the sectional level: 
suppression of secondary cotyledon branches is only found in Allocasuarina sects, Oxypitys, 
Platypitys, Echinopitys and Ceropitys, as were abortion of the primary shoot and divergent tooth 
apices, the latter two characters otherwise found only in A. monilifera and A. microstachya. Seedlings 
of sect. Ceropitys showed a distinctive growth habit making them look like Lycopodium shoots with 
outgrowths resembling microphylls. 
Introduction 
The Casuarinaceae are an unusual family of dicotyledons from SE Asia, Australia and 
Oceania. Within the Casuarinaceae there are four genera and about 80 species of which 
three genera and 66 species occur in Australia, most of which are endemic (Johnson 
& Wilson 1993). Bentham (1873) classified the species largely on cone bracteoles 
(valves), whereas Diels and Pritzel (1905) emphasised features of the vegetative 
branchlets. Modern relationships in the family are based largely on Poisson's (1874) 
division of Casuarina sens. lat. into the Gymnostomae (= Gymnostoma) and Cryptostomae 
(the remainder) using stomatal features. Barlow (1959) divided the Cryptostomae into 
'Group A' and 'Group B' based on cytology, and Johnson (1982) expanded Barlow's 
ideas, establishing Allocasuarina for Group B with Group A representing Casuarina 
s. str. The Gymnostomae were raised to generic rank as Gymnostoma (Johnson 1980) with 
c. 18 species from SE Asian wet tropical forests, and Ceuthostoma for two Malesian 
Gymtwstoma-like species which lack a broad bract under the bracteole pair and which 
possess antrorse anthers and very long-bracteolate cones on long branchlets 
(Johnson 1988). 
There are three genera in Australia (Wilson & Johnson 1989): Gymnostoma has a single 
extant native species, although fossil evidence suggests that the genus was much more 
diverse during the Eocene (Christophel 1980, Scriven & Christophel 1990) and 
Palaeocene (Scriven & Hill 1995). Casuarina has six widespread native species, 
generally on fertile soils, whereas the endemic Allocasuarina with 14 sections and 60 
species is frequently associated with nutrient-deficient soils (Wilson & Johnson 1989). 
Although many Allocasuarina sections are mono- or oligotypic, most species belong to 
sect. Cylindropitys (29 spp.) or sect. Ceropitys (nine spp.). Cylindropitys, in particular, 
consists of many closely related taxa thought to represent a recent evolutionary 
radiation (Wilson & Johnson 1989). 
