Phylogenetic relationships within the Australasian venomous snakes of the genus Pseudechis

The six species of this monophyletic assemblage of large terrestrial proteroglyphous snakes are widely distributed through Australia and southern New Guinea. Data on cytogenetics, scalation, general morphology, and electrophoretic patterns of blood proteins were used to investigate relationships within this group. Chromosomally, P. australis (2N = 38) differs from other Australian taxa (2N = 36), but it is most similar to P. butleri in detailed morphology of the sex chromosomes. P. colletti and P. guttatus also are closely related whereas P. porphyriacus is divergent. The same groupings are apparent from electrophoretic studies of 18 protein systems (representing 27 presumed genetic loci) and in morphological analyses. Morphological data ally the New Guinea species, P. papuanus, with P. colletti.

Results from the various techniques are congruent, and they shown an ancestral stock differentiated into two groups: (1) P. porphyriacus, a viviparous diurnal species from cool and mesic habitats in eastern Australia, and (2) the other five species, which are oviparous, primarily crepuscular or nocturnal, and restricted to warm (often arid) environments throughout Australia and southern New Guinea. Within the oviparous radiation, two species of extreme xeric areas (P. australis, P. butleri) are closely related to each other. Pseudechis guttatus is intermediate between this group and another species-pair (P. colletti and P. papuanus). Despite their widely different habitats, the Pseudechis species are conservative in morphology, karyology, and general ecology. Subdivision of the genus is not recommended.