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Plant Diversity - Flowering Plants
At the end of the Jurassic Period, plants passed another evolutionary milestone with the emergence of the flowering plants in the fossil record. These were the precursors to the modern plants with their more advanced pollination mechanisms. Starting from West Gondwana in what is now western Africa and eastern South America, the flowering plants (called Angiosperms) spread across the supercontinent just as it was beginning to break apart at the beginning of the Cretaceous period. At one stage, it was thought that the Angiosperms might have originated in northern Queensland because of the large number of primitive Angiosperms we have today, but the fossil record has shown otherwise.
At the time of the World Heritage listing of the Wet Tropics in 1988 it was thought that the most primitive and ancient orders of living flowering plants were the Magnoliales and Laurales. At that time there were thought to have been 19 Angiosperm families considered as 'primitive', 13 of which occurred in the Wet Tropics giving it the highest concentration of such families on earth.
Recent major advances in the understanding of evolutionary relatedness amongst plants based on molecular sequencing (phylogenetics) have resulted in a major reassessment of the concept of ‘primitive’ plants. What is actually of interest is the identification of those lineages that appear to have branched off the main evolutionary trunk of the angiosperm family tree at a very early stage. These are now commonly referred to as near-basal lineages (i.e., the group closest to the first angiosperm).
A phylogenetic reassessment of the World’s flora has raised the number of near-basal (or ‘primitive’) families from 19 to 28. The Wet Tropics can claim 16 of these near-basal families, all of which are found in rainforest habitats. These 16 families contain 46 genera and 175 species. (see Table below). The rainforests of the Wet Tropics support a great number of families which can be described as originating from lineages that branched near the base of the angiosperm family tree. These families, genera and species encapsulate, in a genetic sense, a great deal of evolutionary history.
The significance of the flora of the Wet Tropics being a stronghold of near-basal lineages, and the high level of endemism within them, is that it is indicative of a very long history of rainforest habitats persisting in the region and their long isolation from developing floras in other parts of the tropics. South America and Africa separated from Gondwana much earlier (167 million years ago) than the separation of Australia from New Zealand and New Caledonia (70 mya).
Table. The families of primitive plants found in the rainforests of the Wet Tropics. Genera in bold are endemic, and numbers in parentheses indicate the number of Wet Tropics species in each genus.
Family |
Genera |
Annonaceae |
Cananga (1), Desmos (2), Fitzalania (1), Goniothalamus (1), Haplostichanthus (5), Meiogyne (3), Melodorum (4), Miliusa (2), Polyalthia (4), Pseuduvaria (5), Uvaria (1), Xylopia (1)
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Aristolochiaceae |
Aristolochia (2), Pararistolochia (4) |
Atherospermataceae |
Daphnandra (1), Doryphora (1), Dryadodaphne (1) |
Austrobaileyaceae |
Austrobaileya (1) |
Cabombaceae |
Brasenia (1) |
Calycanthaceae |
Idiospermum (1) |
Ceratophyllaceae |
Ceratophyllum (1) |
Eupomatiaceae |
Eupomatia (2) |
Hernandiaceae |
Hernandia (2) |
Himantandraceae |
Galbulimima (1) |
Lauraceae |
Beilschmiedia (9), Cassytha (1), Cinnamomum (4), Cryptocarya (28), Endiandra (29), Lindera (1), Litsea (8), Neolitsea (2) |
Monimiaceae |
Austromatthaea (1), Endressia (1), Hemmantia (1), Hedycarya (1), Levieria (1), Palmeria (2), Steganthera (6), Wilkiea (10) |
Myristicaceae |
Myristica (2) |
Nymphaeaceae |
Nymphaea (2) |
Piperaceae |
Peperomia (5), Piper (9) |
Winteraceae |
Bubbia (4), Tasmannia (3) |
If you are keen to learn about Australian plants in more detail, we recommend that you browse one of the online booksellers for titles on Australian rainforest plants.
To spark your interest, here are just a few primitive flowering plants. See also the story about the Green Dinosaur.
Austrobaileya
 A primitive vine, Austrobaileya is rare and endemic to the Wet Tropics (found nowhere else). It is the only species in its family and it is confined to very wet rainforests from low to upland altitudes. Austrobaileya (Austrobaileya scandens) is a canopy liane which reaches about 15 metres (50 feet). Its leaves are an odd bluey-green colour but its flowers are the giveaway that it is one of the earlier representatives of flowering plants. Its flower parts are arranged in a spiral and the petals are a pale green colour. Flies are the only pollinator and to ensure they are attracted, the flowers smell like rotting fish! Apricot coloured fruits of an oblong shape, up to 70mm by 50mm (2.8 by 2 inches) hang from the vine and contain a packed cluster of chestnut shaped seeds.
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The Native Guava or Copper Laurel
 Many rainforest plants have a great need to ensure they are not self-pollinated and since individuals can be scattered away from each other with lots of dense foliage in between, some species have evolved complicated systems to ensure they can't be self-pollinated. The Native Guava or Copper Laurel has just such a system. Its pollinator is a beetle (which would explain why its flower smells mildly awful) but its flower blooms in two stages. On each tree, the female flower parts are exposed first in the early part of the day. Then this part of the flower closes and the male parts (stamens) are extended. This ensures that any one tree can't be self-pollinated. The Native Guava (Eupomatia laurina) is a relic, primitive species with its entire family composed of only one genus with three species.
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The Pepper Tree
The Pepper Tree (Tasmannia membranea) gets its name from the taste of its seeds rather than its bland fruit. This tree is from one of the earliest flowering plant families known - Winteraceae - making it a true relic of the rainforest. The Pepper Tree is more like a large shrub than a tree, only reaching 3 metres (10 feet) in height. It shares a characteristic with the less developed cycads - that is, the Pepper Tree has separate male and female flowers on different plants.
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Myristica
Ducula bicolor, the scientific name of the Torres Strait or Pied Imperial Pigeon means "eater of Myristica" or put more commonly, "eater of nutmeg". Myristica is a genus containing only three species in the Wet Tropics, one of which we know as the Queensland Nutmeg. The rust coloured, ovoid shaped fruit, 20mm (¾ inch) in size is the favourite food of the Pied Imperial Pigeon, hence its scientific name. Queensland Nutmeg (Myristica globulosa subsp. muelleri) could be used for the commercial production of the spice nutmeg but a similar species from the Solomons is used instead. (Myristica fragrans from the Moluccas yields the commerical spices nutmeg (seeds) and mace (arils).)This 15 metre (50 foot) tree is another example of a primitive flowering plant, and also has separate trees for male and female flowers.
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