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Botany and Ecology of the 'Nightcap Oak', Eidothea hardeniana
Peter H. Weston and Robert M. Kooyman
A new species of Eidothea, a genus of rainforest trees that was only named in 1995, was discovered in the Nightcap Range, near Lismore in north eastern New South Wales in September 2000. Eidothea belongs to the plant family Proteaceae, which also includes more familiar members such as the waratahs, grevilleas, banksias, macadamias and proteas.
History of the Discovery
|Investigating the characteristics of Nightcap Oak
Photo: Peter Weston
Lack of due recognition has long been a problem for Eidothea. The prickly juvenile leaves of the Nightcap species were first found in the 1950s and sent to the Queensland Herbarium in Brisbane, where they were incorrectly identified as belonging to the Corynocarpaceae, a plant family only distantly related to the Proteaceae. Over forty years later, one of us (RMK), then a forest ecologist with State Forests of New South Wales, also noticed the unusual juvenile leaves sprouting from the base of a large tree trunk but found them impossible to identify. After leaving State Forests, he was contracted by the National Parks and Wildlife Service to conduct surveys of rare or threatened plant species in Nightcap National Park, bringing him back to his mystery trees. The next time he encountered one, he noticed a patch of exposed dead wood on the trunk, which revealed the distinctive wood grain of the Proteaceae.
Kooyman collected foliage, wood and rat-gnawed fruits and sent them to the Royal Botanic Gardens Sydney for identification. The other member of our dynamic duo, Principal Research Scientist Dr Peter Weston, who specialises in the classification of the Proteaceae, was then able to confirm that the new species was an Eidothea.
We collaborated in writing a scientific paper describing and naming the new species (Weston & Kooyman 2002). The name hardeniana honours our friend and colleague Gwen J. Harden, whose career has been devoted to improving our knowledge of the flora of New South Wales (she edited the series of that name), particularly of the States rainforest plants.
What does E.hardeniana look like?
Here is a morphological description of E.hardeniana:
Andromonoecious trees 15-40 m high, with one main trunk to 70 cm diameter at breast height, but often with up to 40 smaller subsidiary shoots branching from the base. Hairs simple. Leaves narrowly elliptical to oblanceolate or lanceolate, mostly 8-15 cm long, 1.7-5 cm wide, crowded in false whorls of 3-7 (occasionally with as few as 2 or as many as17). Juvenile leaves (plants 1-1.5 m high) with spiny-toothed margins with 9-20 teeth, each bearing a spine 1-4 mm long. Adult leaves with entire margins. Leaf venation more prominent on the upper leaf surface than the lower when dried. Inflorescences lateral, in leaf axils or on bare twigs, a shortly stalked, 7-11-flowered head, with one or two central flowers, one of which may be bisexual, surrounded by a false whorl of male flowers. Flowers radially symmetrical, creamy white, lacking nectaries. Male flowers with perianth 8.0-9.6 mm long, glabrous externally; basal tubular part of perianth 2.2-3.3 mm long; staminal filaments free or almost so, thread-like, not supporting the anthers, 3.7-6.5 mm long; anthers narrow-oblong, without terminal appendages, 4.0-5.0 mm long. Bisexual flowers slightly larger than the male flowers; ovary densely covered in ascending hairs; style terete, the tip not modified as a pollen presenter; stigma bilobed. Fruits drupaceous (having a structure like a plum), broad-ovoid to broad-ellipsoidal, 3.5-4.0 cm long, 3.0-3.7 cm diameter, green maturing to dull golden yellow; pyrene (stone) broad-ovoid to broad-ellipsoidal, with a rounded base and sharply pointed tip, with several longitudinal ribs on the inside of the endocarp (woody part surrounding the seed).
This description contains some botanical gobbledygook, which we try to explain below.
- Hairs simple. This just means that the hairs are not branched, unlike, for example, Grevillea, in which many of the hairs have two arms.
- Narrowly elliptical to oblanceolate or lanceolate. Widest at or slightly above the middle.
- With entire margins. The margins lack spines or teeth.
- Inflorescences. These are the flower clusters.
- Flower structure. Most proteaceous flowers have four main parts: a perianth of four petal-like tepals, one to four nectaries, four stamens (the male organs that produce pollen in their anthers) and one (the female part of the flower). The pistil is usually differentiated into a basal ovary, and a narrower, longer style, which bears the stigma at its tip. Pollination involves the transfer of pollen grains from anthers to the stigma, on which they germinate, pushing pollen tubes through the inside of the style to the ovary, which then develops into a fruit. In many Proteaceae, the tip of the style just below the stigma is swollen and functions as a pollen presenter. In these plants, the anthers open while the flower is still a bud, shedding their pollen onto the pollen presenter, which presents the pollen to the pollinator. Eidothea hardeniana is very unusual in the Proteaceae in sometimes having bisexual flowers with five tepals.
- Andromonoecious. Most members of the Proteaceae (indeed most flowering plants) have only bisexual flowers flowers with both male and female organs (stamens and pistils respectively). Eidothea differs from these and resembles a few other taxa in the Proteaceae (eg. Placospermum, Sphalmium, Stirlingia) in bearing two different kinds of flowers: male flowers (having stamens, but lacking pistils) and bisexual flowers, a condition called andromonoecy.
- Fruits drupaceous. This means that the fruits has a structure like a plum, with a seed surrounded by a woody layer (the endocarp), which together constitute the stone (pyrene in botanical jargon), surrounded in turn by a thick, fleshy layer (the mesocarp) and an outer skin (the epicarp).
Flower buds (bottom)
Photos: Peter Weston
Ecology of Eidothea hardeniana
E.hardeniana is a rainforest tree, occurring in upland cool and riparian simple notophyll vine forest (to notophyll vine forest) on soils derived from acid volcanic rocks (rhyolite lithology). Dominant tree species include Ceratopetalum apetalum (Coachwood), Endiandra introrsa (Dorrigo Plum), Canarium australasicum, Schizomeria ovata (Crabapple), Austrobuxus swainii (Pink Cherry), Cinnamomum oliveri (Olivers Sassafras), sometimes with occasional emergents including Lophostemon confertus (Brush Box), Callitris macleayana (Stringybark Pine) or Tristaniopsis collina (Mountain Water Gum).
E.hardeniana flowers from mid October to mid November. The pollinators are not known, but preliminary study (P. Bernhardt, R.M. Kooyman and P.H. Weston, unpublished data) suggests they may include hover flies and beetles. The fruits take over one year to develop, reaching full size in about mid December, then changing colour from green to dull yellow over the following two to three months, falling from mid February to early March. The fruits are gathered by rats, which accumulate them in hidden piles, and which gnaw through the fruit wall to eat the seed.
E.hardeniana is listed as an endangered species on Schedule 1 of the Threatened Species Conservation Act, 1995 and is known to occur in Nightcap National Park and in the adjacent Whian Whian State Forest.
E. zoexylocarya, the only other species of Eidothea, is known only from Mt Bartle Frere, near Cairns in North Queensland. The discovery of another species in New South Wales was exciting for a number of reasons.
The Proteaceae is a very old family of flowering plants that probably originated while the ancient supercontinent Gondwana was still in one piece. Gondwana consisted of what are now the continents of Australia, Africa, South America and Antarctica, as well as smaller bits and pieces such as New Zealand, New Caledonia and Madagascar. Gondwana began splitting up over 120 million years ago and the fragments carried a diverse array of plants and animals with them, including a variety of lineages of the Proteaceae. Eidothea is the only relic of one of those early lineages that has barely survived in the rainforests of eastern Australia. Other lineages went on to diversify spectacularly, resulting in hundreds of descendant species.
Why did Eidothea not flourish like those others? One possible explanation is that it was incapable of adapting to changing environments. We know that its appearance has not changed much for a long time because fossil fruits that look just like those of living Eidothea are known from rocks that are 15-20 million years old. These fossils were discovered in the 19th century in the Victorian goldfields by the State Government Botanist of the day, Baron Ferdinand von Mueller. The fruits are so unlike those of other Proteaceae that Mueller misidentified the fossils as belonging to something in the olive family. It was not until the fossils were matched with fruits from living Eidothea trees that their true identity was revealed.
That Eidothea has been found at localities as far apart as Cairns, Lismore and Ballarat, also underlines the fact that Australias rainforests are tiny remnants of ancient rainforests that covered vast areas of Australia until only a few million years ago. This makes them a particularly precious part of our natural heritage. Similar distributions are found in a whole range of other plants and animals that are now restricted to small rainforest pockets along Australias eastern margin from Tasmania to North Queensland.
Perhaps the most important implication of the discovery of E.hardeniana is that New South Wales is still a fantastically exciting place to do botanical research. It is a large rainforest tree, growing to over 40 meters in height. It lives in a well-botanised area some of Australias most experienced rainforest ecologists have scoured the Nightcap Range over the last 50 years. It grows in a relatively accessible place - you can drive a family sedan to within 100 metres of a couple of the trees. It is a highly significant evolutionary relict. Isnt it amazing that such a plant could evade detection until now? If the Nightcap Oak could hide so effectively, how many smaller, or less distinctive, but nonetheless important plant species are still lurking in our wild places, awaiting discovery?
Is Eidothea hardeniana as significant a discovery as the Wollemi Pine?
This is a frequently asked question, the short answer to which is no.
The main reason for saying this is that another species of Eidothea was already known from North Queensland when E.hardeniana was discovered. The botanical significance of the two genera is comparable but only one living species of Wollemia is known (Wollemia nobilis). Below are some useful points with which to compare the two genera.
Number of species:
Distribution of living species:
Wollemia: Wollemi National Park, central tablelands, NSW
Eidothea: Mt Bartle Frere and Mt Pieter Botte, NE Queensland (E.zoexylocarya), Nightcap Range, NE NSW (E.hardeniana)
Wollemia: Agathis (kauri pines), Araucaria (Norfolk Pine, Hoop Pine, Bunya Pine, Monkey Puzzle, etc.) (see Gilmore & Hill 1997)
Eidothea: 24 genera in Proteaceae subfamily Proteoideae, including Protea, Leucadendron, Leucaspermum, and most other South African Proteaceae, Isopogon (Australian drumsticks), Adenanthos (Australian jugflowers), Petrophile (Australian conesticks), Conospermum (Australian smoke-bushes) (see Hoot & Douglas 1998)
Estimated age of lineage (based on a combination of fossil evidence, the known evolutionary relationships of the two genera, biogeography and known timing of continental drift):
Wollemia: 90-200 million years
Eidothea: 90-130 million years
Oldest known fossil:
Wollemia: 90 million years (fossil pollen of dubious identity)
Eidothea: 15-20 million years (fossils of the very distinctive fruits from Western Victoria)
Number of known adult individuals in the wild:
Wollemia nobilis: 41
Eidothea hardeniana: 93
Eidothea zoexylocarya: unknown, but probably hundreds, possibly thousands
Gilmore, S., and Hill, K.D. (1997) Relationships of the Wollemi Pine (Wollemia nobilis) and a molecular phylogeny of the Araucariaceae. Telopea 7: 177-302.
Hoot, S.B., and Douglas, A.W. (1998) Phylogeny of the Proteaceae based on atpB and atpB-rbcL intergenic spacer region sequences. Australian Systematic Botany 11: 301-320.
Weston, P.H. & Kooyman, R.M. (2002) Systematics of Eidothea (Proteaceae), with the description of a new species, E. hardeniana, from the Nightcap Range, north-eastern New South Wales. Telopea 9: 821-832.
Peter Weston: Royal Botanic Gardens Sydney, Mrs Macquaries Road, Sydney 2000
Robert Kooyman: Earth Process Ecological Services, 220 Dingo Lane, Myocum, 2482
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Australian Plants online - December 2003
Association of Societies for Growing Australian Plants