National recovery plan for the Nightcap Oak (Eidothea hardeniana)

Threatened Species Unit, Western
New South Wales Department of Environment and Conservation, 2004
ISBN: 0 7313 6781 2

3. Species Information

3.1 Description and Taxonomy

The Nightcap Oak is in the Proteaceae family. The Proteaceae family contains many well-known Australian genera such as Banksia, Grevillea, Macadamia and Telopea (Waratah).

Proteaceae is the fifth largest family of the Australian flora in terms of number of species (Harden et al. 2000). It is an ancient family of flowering plants that probably originated while the supercontinent of Gondwana was still intact. Gondwana began splitting up over 120 million years ago and the fragments carried a variety of lineages of the Proteaceae (White 1994). The genus Eidothea is the only relic of one of those early lineages, surviving in the rainforests of eastern Australia.

The Nightcap Oak was discovered in 2000 by consultant botanist Robert Kooyman during survey work in the Nightcap Range. The genus itself was described as recently as 1995 from a species (Eidothea zoexylocarya) discovered on Mt Bartle Frere in north Queensland (Douglas & Hyland 1995). The Mt Bartle Frere species bore a close resemblance to a fossil fruit (Xylocaryon lockii) described in 1875 by botanist Baron Ferdinand von Mueller from the Ballarat region in Victoria. The fact that representatives of the Eidothea genus have been found at localities as far apart as north Queensland, north-east NSW and Victoria illustrates that rainforest once covered vast areas of eastern Australia.

The following description was provided by Peter Weston of the Botanic Gardens Trust:

Rainforest trees 1540 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. Bark grey, compact. Branchlets glabrous. Leaves narrowly elliptical to oblanceolate or lanceolate, mostly 815 cm long, 1.75 cm wide, crowded in false whorls of mostly 37. Juvenile leaves with toothed margins with 920 teeth, each bearing a spine 14 mm long. Adult leaves with entire margins. Leaf venation more prominent on the upper leaf surface than the lower when dried. Hairs simple. Inflorescences lateral, in leaf axils or on bare twigs, a shortly stalked, 711-flowered head, with a central, bisexual or male flower or flower pair, surrounded by a false whorl of male flowers. Flowers ± actinomorphic, creamy white, lacking nectaries. Male flowers with perianth 8.09.6 mm long, glabrous externally; basal tubular part of perianth 2.23.3 mm long; staminal filaments free or almost so, thread-like, not supporting the anthers, 3.76.5 mm long; anthers narrow-oblong, without terminal appendages, 4.05.0 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, broad-ovoid to broad-ellipsoidal, 3.54.0 cm long, 3.03.7 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.

Figure 1 illustrates the adult leaves and flowering shoot of the Nightcap Oak, and Figure 2 illustrates the flower structures.

3.2 Distribution

The Nightcap Oak is known from a very limited area in the Nightcap Range on the upper north coast of NSW, north east of Lismore. The trees are scattered across a few hectares.

Figure 1. Adult leaves and flowering shoot of the Nightcap Oak. Scale bar = 2cm

3.3 Land Tenure

The Nightcap Oak occurs on DEC estate. It is not known to occur on any other land tenure. Details of locations have not been included to maintain site confidentiality.

3.4 Habitat

The Nightcap Oak grows in simple notophyll/microphyll vine forest (Webb 1959) (warm temperate rainforest) on rhyolite geology.

Vegetation

The rainforest tree Ceratopetalum apetalum (Coachwood) is a dominant or co-dominant canopy and sub-canopy species in the Nightcap Oak habitat (Kooyman 2001). Large emergent trees such as Tristaniopsis collina (Mountain Water Gum), Lophostemon confertus (Brush Box), Syncarpia glomulifera (Turpentine), Callitris macleayana (Stringybark Pine), and Araucaria cunninghamii (Hoop Pine) occasionally occur in these rainforest communities.

Three Floyd (1990) suballiances can be recognised in the Nightcap Oak habitat, namely; 33 (Ceratopetalum/Schizomeria-Argyrodendron/Sloanea), 35 (Ceratopetalum/Schizomeria-Caldcluvia) and 45 (Tristaniopsis collina-Ceratopetalum/Schizomeria) (Kooyman 2001). Forest Type mapping, a classification based on dominant canopy species, is used in most areas of state forest estate (Forestry Commission of NSW 1989). Four forest types (FT), or combinations of forest types, are recognisable in the Nightcap Oak habitat. These are FT 2 (Sloanea woollsii), FT 11 (Tristaniopsis collina/Schizomeria ovata), FT 13 (Tristaniopsis collina/Ceratopetalum apetalum) and FT 53 (Lophostemon confertus). Table 1 lists the common species in the Nightcap Oak habitat and gives a comparison between vegetation classifications.

Threatened and significant species

Seven NSW threatened plant species occur in the Nightcap Oak habitat. These are listed in Table 2.

Plant species listed as rare by Briggs and Leigh (1996) that occur in the Nightcap Oak habitat include Acacia orites, Argophyllum nullumense, Austrobuxus swainii, Gahnia insignis, Helmholtzia glaberrima and Pararistolochia laheyana. Examples of species associated with the Nightcap Oak that also has biogeographical significance includes the rare Dorrigo Plum (Endiandra introrsa), a species found only on the Nightcap Range and in the Dorrigo region.

Figure 2. Flower structures of the Nightcap Oak showing male and female flower parts

Table 1. Common species, Floyd sub-alliances, and Forest Types in the Nightcap Oak habitat
Common species Floyd suball SFNSW FT.
Ceratopetalum apetalum, Endiandra introrsa, Sloanea woollsii, Canarium australasicum, Syzygium luehmanii, Schizomeria ovata, Caldcluvia paniculosa, Quintinia sieberi, Randia benthamiana, Triunia youngiana, Cryptocarya meissneriana, Wilkiea huegeliana, Linospadix monostachya, Blechnum cartilagineum, Adiantum formosum, Lomandra longifolia. 33 FT 2/11
Ceratopetalum apetalum, Schizomeria ovata, Caldcluvia paniculosa, Anopterus macleayanus, Endiandra introrsa, Austrobuxus swainii, Triunia youngiana, Helicia ferruginea, Linospadix monostachya, Lomandra longifolia. 35 FT 11
Tristaniopsis collina, Araucaria cunninghamii, Ceratopetalum apetalum, Endiandra introrsa, Schizomeria ovata, Canarium australasicum, Quintinia sieberi, Anopterus macleayanus, Triunia youngiana, Wilkiea huegeliana, Linospadix monostachya, Citriobatus pauciflorus, Blechnum cartilagineum, Lomandra longifolia. 45 FT 13,
FT 11/13
Lophostemon confertus, Callitris macleayana, Tristaniopsis collina, Ceratopetalum apetalum, Cinnamomum oliveri, Austrobuxus swainii, Synoum glandulosum, Schizomeria ovata, Cryptocarya meissneriana, Wilkea huegeliana, Triunia youngiana, Lomandra hystrix, Lomandra longifolia. 33 or 35 with L. confertus FT 53/11, & 53
Table 2. Threatened plant species associated with the Nightcap Oak
Species Common Name Status*
Corokia whiteana Corokia V
Elaeocarpus sp.
'Rocky Creek'
Minyon Quandong E
Endiandra hayesii Rusty Rose Walnut V
Hibbertia hexandra   E
Hicksbeachia pinnatifolia Red Bopple Nut V
Symplocos baeuerlenii Small-leaved Hazelwood V
Uromyrtus australis Peach Myrtle E

*TSC Act status - E = endangered; V = vulnerable

Physiography

The Nightcap Range forms part of the southern rim of the erosion caldera of the Mt Warning Shield Volcano. This area is dominated by Nimbin rhyolite, which overtopped the initial basalt flows from the Mt Warning volcano (Adam 1987). The yellow podzolic soils produced from rhyolite have a lower fertility than the basalt-derived soils and support vegetation with a lower species diversity than that of the basalt areas.

The elevation of the Nightcap Range varies from approximately 200 m Australian Height Datum (ahd) to just over 800 m ahd. The Nightcap Oak occurs above 300m ahd.

Climate

The Nightcap Range experiences a subtropical climate with heavy summer-autumn rainfall and a relatively dry winter. Cyclonic activity further to the north is often associated with heavy, intense rainfall events, and infrequent cyclonic winds can cause extensive local destruction.

The Nightcap Range has a very high annual rainfall with an average of over 2500 mm per annum (Graham 2001). Figures for nearby areas have a mean annual rainfall of 1358 mm (Lismore) and 1687mm (Murwillumbah) and a mean temperature range of between 19.1oC and 29.7oC (Lismore) and 19.1oC and 29.5oC (Murwillumbah) (CSIRO 1996). The climate of the Nightcap Range varies somewhat from these figures due to its higher elevation, resulting in lower temperatures and significantly higher rainfall due to the orographic effect of the range.

3.5 Life History and EcologyLife cycle

As the Nightcap Oak can grow to be a tall canopy tree, it is presumably a long-lived species. Information to date indicates that the species may flower annually from early November (it has flowered for the past three seasons since discovery), and sets fruit approximately 1518 months after flowering. Mature fruit have been collected from February to May.

Seed viability

Observations indicate that fruit of the Nightcap Oak takes over one year to develop. The fruit is difficult to detect until it ripens to yellow on the tree.

For seed of the Nightcap Oak to germinate, the woody endocarp must be removed or at least partially removed to allow water to penetrate to the seed. Exposed seeds from freshly matured fruit take up to six months to germinate at about 25oC in glasshouse conditions (Offord and Azzopardi 2002). No germination has been recorded from fruit collected from the ground, which may indicate a short life of seeds, possibly one to three years (Offord pers. comm.). It is presumed that seedlings arise from fruit in which the endocarp is broken down naturally within a relatively short space of time following maturity. Seed biology of this species requires further examination.

Population structure

Comprehensive surveys by Kooyman (2001) indicate that the species has a small population size of approximately 100 mature individuals. Maturity is based on size class and is arbitrarily measured as individuals with a diameter at breast height over bark (dbhob) greater than 10 cm. Of the mature individuals, 20 (12% of whole population) have a dbhob greater than 50 cm. Kooyman (2001) recorded 84 individuals (47% of whole population) with a dbhob of less than 1.5 cm (immature).

Predators and parasites

Known seed predators of the Nightcap Oak include small mammals, probably the Bush Rat Rattus fuscipes and possibly a Melomys (based on residual tooth marks on inner pericarp remains). These mammals eat the seeds by carefully removing the very bitter outer flesh before chewing through the hard layer to gain access to the edible core of the drupe. Seed predation appears to occur after the fruits have fallen to the ground. It appears that a significant proportion of the seeds are damaged and eaten, although seedlings are present at a number of sites, suggesting that adequate recruitment is occurring despite predation. It is possible that R. fuscipes may assist with dispersal by caching fruit.

In north Queensland, Eidothea zoexylocaryon seeds are eaten by small mammals, (probably Giant White-tailed Rats Uromys caudimaculatus), with hollowed fruit of various sizes often found on the ground around the tree (Harden et al. 2000). These rats eat the nuts while the fruits are still on the trees.

Leaf suckers such as pit-galling psyllids, and leaf miners have a minor impact on the leaves of the Nightcap Oak. This minor impact does not rule out the possibility of periodic irruptions.

Pollinators

In Australia, field observations indicate that members of the Proteaceae are visited by a wide range of pollinators including birds, mammals, and insects (Maynard 1995). The flowers of the Nightcap Oak lack nectar glands and pollen is the only edible reward for visiting insects. This finding narrows the range of prospective pollinators (Bernhardt 1996).

Preliminary field investigations conducted in November 2001 and 2003 (Weston, Kooyman and Bernhardt, unpublished data) found that the most abundant pollen feeders on flowers of the Nightcap Oak were various species of beetles, both diurnal (primarily Diphucephala:Scarabidae and an unidentified genus of Chrysomelidae) and nocturnal (unidentified genus of Alleculinae:Tenebrionidae and an unidentified genus of Chrysomelidae). Less common pollen feeders were nocturnal katydids (Zaprochilus:Orthoptera) and diurnal hover flies (Melangyna:Syrphidae). Some of these species have already been found to carry small quantities of Nightcap Oak pollen, and the others are presently the subject of active investigation.

The morphology, colour and scent of inflorescences and flowers of the Nightcap Oak is consistent with insect pollination, a prediction that is tentatively confirmed by the observations described above. However, available data are too meagre to draw conclusions as to whether any of the observed visitors are effective pollinators, or that those observed to date are the predominant insect visitors. Another potentially limiting factor is whether the breeding system of the Nightcap Oak is self-compatible (accepts its own pollen to form healthy seeds) or self-incompatible (must be cross-pollinated with another tree to form healthy seeds). Self-incompatible species are more vulnerable to inbreeding depression than are self-compatible species (Frankham et al. 2002). Preliminary genetic data (Rossetto, unpublished data; section 5.4) strongly suggest that the Nightcap Oak is predominantly outcrossing (section 5.4). However, observations of the behaviour of insect visitors (Weston, Kooyman and Bernhardt, unpublished data) suggest that most pollen transfers between anthers and stigmas occur on the same inflorescence. This suggests that Nightcap Oak is likely to be self-incompatible.

Studying the reproductive biology of large rainforest trees like Eidothea is difficult because the flowers of wild plants are relatively inaccessible. Only one tree of the Nightcap Oak has reproductively mature shoots that can be reached from ground level and this tree has been the sole subject of all pollinator observations so far. The canopies of other trees could be reached using various techniques, however such techniques may injure individual trees. The breeding system could be characterised with crossing experiments conducted on cultivated plants propagated from reproductively mature shoots gathered from the canopies of adult trees. It is possible to strike cuttings from reproductively mature shoots but it is not known how long it takes for such cuttings to flower and set fruit.

Disturbance

There is no information available on the response of the Nightcap Oak to disturbance. As the species occurs in mature phase rainforest it is likely to be adversely impacted by changes that alter or impact upon this habitat type.

3.6 Ability of Species to Recover

It is not known whether the Nightcap Oak has declined in recent times. It is not known whether the current population size is adequate to maintain the species in the long term. As the Nightcap Oak is a long-lived tree, changes in the habitat may take some time to show an impact on the species as a whole.