146 DAVID J. CANTRILL & IMOGEN POOLE
Fig. 5. Floristic provincialism across Gondwana derived from Herngreen el al. (1996). Note the regional
differences in abundance of key trisaccate species such as Microcachyridites antarcticus within the Trisaccate
Province. Histograms show, percentage abundance of M. antarcticus in Lower Cretaceous strata: (A) from
Dettmann & Thomson (1987); (B) southeastern Australia from Dettmann (1986b), central Australia from
Burger (1980).
Bryophytes/Hepatophytes
In the earliest Cretaceous, bryophytes and
hepatophytes form an important and character-
istic component of the floristic diversity. Not only
are they diverse, accounting for up to 20% of the
species (Fig. 4C), but they are also ecologically
abundant ranging from colonizers of fresh
sediment to components of established fern
thickets and forests (Cantrill 1997). Indeed,
many localities are characterized by assemblages
comprising just hepatophytes, where they can
cover individual bedding surfaces for hundreds
of metres. This is also true for other southern
high-latitude sites (e.g. southeastern Australia;
Douglas 1973) and appears to be a phenomenon
of high latitude floras in the early part of the
Mesozoic (Cantrill 1997). The highest hepato-
phyte diversity occurs in the Early Cretaceous
but they rapidly become a minor constituent of
the vegetation by the Late Cretaceous. This
pattern is also reflected in the microfloral
diversity (Fig. 4C).
Conifer ales
Conifers generally maintain between 10 and
20% of the within-flora diversity through the
Cretaceous interval (Fig. 4D). This is apparent
from the microfloral record but is less clear in
the macroflora. The macrofloral record shows a
distinct drop in within-flora diversity in the
mid-Cretaceous. The differences may be due to
wind-dispersed conifer pollen representing a
wider range of plant communities than those
seen in the macrofloras.
Pteridophytes and lycophytes
Macrofloral remains are most diverse in the
Early Cretaceous but decline towards mid-
Cretaceous times (Fig. 4E). Following this
decline ferns recover through the later part
of the Cretaceous (Fig. 4E). This pattern is
supported by the microfloral record, which
suggests that the recovery continues through the
Late Cretaceous (Fig. 4E). Although a number
of groups show a marked decline in diversity
through the Cretaceous (e.g. Dipteridaceae),
other families remain relatively stable (e.g.
Gleicheniaceae). In terms of abundance, ferns
show a similar pattern to the bennettites: they
are extremely common in Aptian and Albian
floras but are less frequently encountered in
Late Cretaceous floras. So, although diverse in
the later part of the Cretaceous, they are
probably less important ecologically.
Angiosperms
Macrofloral remains of angiosperms are not
recorded until the Late Albian (Cantrill &
Nichols 1996) where they make up to 12 % of the
flora. This includes a diversity of habit ranging
