Hwang and Conran, Seedling characteristics (Casuarinaceae) 
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purple. Dilcher et al. (1990) and Scriven and Hill (1995) similarly found that both 
extant and fossil Casuarinaceae can be identified and assigned to genera on the basis 
of vegetative and reproductive anatomy. Red roots in the Casuarinaceae and some 
other families indicate high levels of leghaemoglobin (Martin & Dowd 1993), where it 
is linked to nitrogen fixation by the soil actinomycete Frankia (Maggia & Bousquet 
1994). Although this is common throughout the family, it is mixed enough in its 
occurrence within each of the genera and sections to suggest that the feature has 
limited phylogenetic utility within the family. 
In the Casuarinaceae, there are also several taxa where the seedling characteristics 
differ from those of the adults. For example, lateral branch tooth apices are divergent 
in juveniles of sect. Oxypitys, but appressed in the adults, and appressed in seedling 
A. dielsiana, A. Iieugeliana and A. pusilla (amongst others), but divergent in the adults. 
Similarly, whereas no Casuarina species have divergent teeth in the seedlings, adult 
C. obesa and C. glauca both possess them, hr A. acutivalvis the branchlets changed 
gradually into the adult form, whereas in A. campestris and A. tessellata one or a few 
axillary shoots develop directly with adult morphology. Torrey (1983) also observed 
that adult branchlets develop after about 10 cm of juvenile growth, but in A. acutivalvis 
there can be reversal, where adult shoots revert to the juvenile form. 
A phenetic analysis of the Casuarinaceae by Hwang (1989) using the characters 
described here, plus a series of growth rate-related characters found that there were 
several distinctive species assemblages, representing in decreasing order of 
dissimilarity: Allocasuarina sect. Oxypitys-, a mixed group from Allocasuarina sects 
Ceropitys and Echinopitys; Casuarina sens. str. plus Allocasuarina torulosa (Aiton) 
L.Johnson; and then three groups consisting of mixtures of taxa from the remaining 
Allocasuarina sections sampled (see taxa listed in Hwang & Conran 1991). 
Prider's (1998) viability and embryological studies of Gymnostoma australianum 
demonstrated that the majority of the samaras produced were embryologically non- 
viable rather than short-lived, and that some of the few fertile seeds produced were 
still viable after 2 years. Similarly, Torrey (1983) was uncertain whether germination 
failure in several of the species that he examined was due to seed age or general low 
viability. 
Relationships between series and sections in large genera can often be defined, at least 
in part, on seedling structure. Conran et al. (1997) found distinctive seedling-based 
groups in the Droseraceae which are taxonomically informative at the subgeneric and 
sectional levels, and which indicated that there are previously unpredicted 
relationships between them. Within Acacia (Mimosaceae), seedlings are distinctive at 
the subgeneric level (e.g. Burger 1972) and reflect features which, though present in 
the seedlings, are absent in mature plants. In Eucalyptus (Myrtaceae) the seedlings are 
also different between subgenera and between some of the sections (Chippendale 
1988), with Maiden (1929-31) dividing the genus into three sections on cotyledon 
shape. Similarly, the E.flocktoniae and E. transcontinentalis complexes of series Subulatae 
both possess uniquely decussate-leaved seedlings (Nicolle & Conran 1999). Weberling 
and Leenhouts (1966), Burger (1972) and Li and Hsieh (1997) also noted many 
examples of variable and potentially taxonomically useful seedling characters at the 
intrafamilial and infrageneric levels in a range of rainforest taxa. 
The patterns seen here for some of the seedling characteristics in the Casuarinaceae 
suggest that there are some distinctive seedling-based species groupings. Allocasuarina 
sect. Ceropitys have lycopod-like seedlings, and simple cotyledon branches. 
Allocasuarina sects Dolichopitys, Oxypitys, Platypitys, Echinopitys and Ceropitys, had 
abortion of the primary shoot and divergent tooth apices characters otherwise found 
only in A. monilifera (sect. Cylindropitys) and A. microsiachya (sect. Trachypitys). 
