Palaeofloristic studies of the Antarctic Peninsula region are important in
furthering our understanding of (i) the radiation and rise to ecological
dominance of the angiosperms in the Southern Hemisphere during the Late
Cretaceous and (ii) the present day disjunct austral vegetation.
Investigations of Upper Cretaceous and Early Tertiary sediments of this region
yield a rich assemblage of well-preserved fossil dicotyledonous angiosperm
wood which provides evidence for the existence, since the Late Cretaceous, of
temperate forests similar in composition to those found in present-day
southern South America, New Zealand and Australia. This paper describes two
previously unrecognised morphotypes, which can be assigned to the Monimiaceae
sensu lato, and represents the first record of this
family in the wood flora of Antarctica. Specimens belonging to the first
fossil morphotype have been assigned to Hedycaryoxylon
SÜss (subfamily Monimioideae) because they exhibit anatomical features
characteristic of Hedycaryoxylon and extant
Hedycarya J.R.Forst. & G.Forst. and
Tambourissa Sonn. Characters include diffuse porosity,
vessels which are mainly solitary with scalariform perforation plates,
opposite to scalariform intervascular pitting, paratracheal parenchyma,
septate fibres and tall (>3 mm), wide multiseriate rays with a length:
breadth ratio of approximately 1: 4. Specimens belonging to the second
morphotype have been assigned to Atherospermoxylon
KrÄusel, erected for fossil woods of the Monimiaceae in the tribe
Atherospermeae (now Atherospermataceae) in that they exhibit anatomical
features similar to Atherospermoxylon and extant
Daphnandra Benth., Doryphora Endl.
and Laurelia novae-zelandiae A.Cunn. These characters
include diffuse to semi-ring porosity, scalariform perforation plates with up
to 25 bars, septate fibres, relatively short (<1 mm) rays with a length:
breadth ratio of between 1: 4 and 1: 11.
The secondary xylem of three uncommon genera of Boraginaceae was studied anatomical-Iy and compared to other taxa of this and other families. The two neotropical genera Antrophora and Lepidocordia are similar in their wood anatomy and show only limited resemblance with the subfamily Ehretioideae. On the other hand, the old world genus Pteleocarpa shows hardly any affinity to Boraginaceae. Two of the genera reveal xylem features which are unique within Boraginaceae, and which are matched by an equally unique flower morphology.
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