Threatened Species Unit, North East Branch
New South Wales Department of Environment and Conservation, 2004
3. Species Information
- 3.1 Taxonomy and description
- 3.2 Distribution and population size
- 3.3 Land tenure
- 3.4 Habitat
- 3.5 Life history and ecology
- 3.6 Ability of species to recover
Eleven species of the genus Rapanea occur in subtropical and tropical (eastern) Australia of which four are known to occur in NSW. However, it is proposed to reclassify many of the Rapanea species into the genus Myrsine, including the four species in NSW (B. Jackes, pers. comm.).
The Ripple-leaf Muttonwood has not yet been formally described, however, a description for the species is currently in preparation (B. Jackes, pers. comm.).
The Ripple-leaf Muttonwood is a small evergreen tree or large shrub to 5 m high. The bark is grey to greyish-brown, smooth when young and often roughened by old leaf and fruit bases in larger specimens.
The leaves are elliptic in shape with edges that are entire and usually strongly undulating in the adult leaves (hence ripple leaf). The apex of the leaf is obtuse and the base wedge-shaped. Leaves are 5-14 cm long by 1.5-3 cm wide, simple and arranged alternately on the stem. The petiole (leaf stalk) is 3-5 mm, grooved and may be crimson or purple but is usually green. The midrib is raised on the upper surface of the basal third of the leaf. Clear or cream streaks are usually visible in the leaf and red-orange dots may also be visible (NPWS 1999).
Stems are generally rounded, with scattered hairs but often hairless. The terminal leaf bud is either hairless or has glandular, rusty or white coloured hairs only along its rim. The leaf bud may also have rusty coloured scales.
The flowers of the Ripple-leaf Muttonwood are small, greenish-white with prominent glands. The inflorescence is much shorter than the leaves and is inconspicuous. The flowers are unisexual with parts in multiples of five. The calyx is deeply lobed and persistent. Flowering has been observed in spring and summer.
The fruit is a blue drupe 3-4 mm in diameter and consists of a single round seed wrapped in a very thin coating of flesh. The pedicel (fruit stem) is 2-4 mm and hairless. Orange to red glands are common on young fruits, concentrated towards the apex. Several drupes, each on its own stalk, arise from a single point.
The Ripple-leaf Muttonwood can be distinguished from the more common Rapanea howittiana and R. variabilis. Features used to distinguish the species are the size of the drupe which is 3-4 mm on the Ripple-leaf Muttonwood and 4-8 mm for the other species, and the leaf margin of juvenile leaves which is entire on the Ripple-leaf Muttonwood and toothed on the other species. The leaf texture is also a distinguishing feature, the texture of Ripple-leaf Muttonwood leaves is fine as opposed to being rubbery as they are for R. howittiana or tough like those of R. variabilis (Horton 2000).
The Ripple-leaf Muttonwood occurs only within the NSW North Coast Bioregion. For functional reasons the International Union for the Conservation of Nature and Natural Resources (IUCN) expresses a population number as the number of mature individuals only. Mature individuals is defined as the number of individuals known, estimated or inferred to be capable of reproduction (IUCN 2001). However, to indicate the relative size of the Ripple-leaf Muttonwood populations, both total number of observed plants and estimated number of mature individuals are discussed in this plan. There are three extant populations of the Ripple-leaf Muttonwood which occur within the Richmond River and Clarence River catchments.
Estimating the number of individual plants is difficult as the Ripple-leaf Muttonwood occurs in clusters with many of the stems being suckers from the lateral roots of a parent plant. Each stem or group of stems observed arising from one point in the ground is considered one plant for the purposes of indicating the relative size of the populations. The number of genetically different plants is unknown but is most probably much fewer than the number of plants observed.
One population was found in 1997, located on private property containing a tributary to the Richmond River, near the locality of Tatham. This population consists of at least four plants (Horton 1999a). All of these plants are less than 2 m high. The area of occupancy of this population is 4 m2.
A second population was found in 1998, located in Boatharbour Nature Reserve, adjacent to the Bangalow Road, near the town of Lismore. This population consists of approximately 33 plants (Horton 1999a, Joseph 2000c), including four plants that are large enough to be mature, i.e. greater than 2 m high. The area of occupancy of this population is no more than 250 m2.
The largest known population was found in 1999, located in Mallanganee National Park, west of the town of Casino (Horton 1999b). The population is estimated to be in excess of 370 plants, including at least twelve plants that are large enough to be mature, i.e. over 2 m high. The area of occupancy of this population is no more than 1500 m2.
The known distribution of the species has contracted significantly during the last century. Five botanical samples of the Ripple-leaf Muttonwood that were collected between 1876 and 1903 provide evidence that the species occurred in the Richmond and Tweed River catchments during this period. Two samples of Ripple-leaf Muttonwood were collected by Glen Holmes in 1986 from the Cambridge Plateau (Clarence River catchment) and Ruthven (south of Lismore), however these populations are presumed extinct (Horton 1997). The species was not found again for many years and the Ripple-leaf Muttonwood was presumed extinct until it was rediscovered on the Richmond River floodplain in 1997 (Horton 1997).
Figure 1 Locations of known populations of Ripple-leaf Muttonwood
One of the three populations of Ripple-leaf Muttonwood occurs on private property near Tatham. The forest remnant that contains the species is Zoned 7a Environmental Protection (natural vegetation and wetlands) in the Lismore Local Environmental Plan 2000.
The other two populations occur in Boatharbour Nature Reserve and Mallanganee National Park, both of which are managed by the DEC.
The Ripple-leaf Muttonwood is known to occur at two distinctly different topographical positions within the Richmond River and Clarence River catchments. The Mallanganee population occurs on an upper slope on the western side of the Richmond Range, in the east of the Clarence River catchment. The Boatharbour and Tatham populations occur on the alluvial flats of the floodplains of the Richmond River catchment.
The altitude of known occurrences of the Ripple-leaf Muttonwood ranges from 10 m to 400 m above sea level. Aspect does not appear to be a determining factor.
The Ripple-leaf Muttonwood is known to occur on:
- Focal Peak tertiary volcanics,
- Floodplains enriched with Focal Peak volcanics, and
- Floodplains enriched with either or both the Focal Peak and Mount Warning volcanics.
The soils of the habitat on the Richmond Range near Mallanganee are krasnozems and chocolate basalt loams, which are fertile, relatively stable and well drained. The Ripple-leaf Muttonwood has not been found on the nearby, less fertile soils that developed from the exposed sedimentary (sandstone, siltstone and shale) parent material.
The soils of the habitat on the floodplain are alluvial krasnozem, with a higher clay content than pure krasnozem thus contributing to the high water holding capacity (Floyd 1977).
All locations where the species is known to occur are subject to water stress, either that of extended dry periods and/or periods of inundation. In upland areas, soil saturation may result from extended periods of high rainfall while in lowland areas it may either be associated with localised heavy rain or widespread flooding.
The Ripple-leaf Muttonwood habitat on the Richmond Range experiences a subtropical climate characterised by relatively high rainfall and high temperatures from December to March, and a dry season with cold nights and mild days from June to September. The average annual rainfall between 1936 to 1982 for Urbenville, within the Focal Peak region of the Richmond range, was 1056 mm.
The Ripple-leaf Muttonwood habitat on the floodplain has a similar pattern of rainfall to that on the range but the floodplain populations may be subjected to frosts during winter.
On the Richmond Range near Mallanganee, the Ripple-leaf Muttonwood is known to occur in tall open forest dominated by Brush Box (Lophostemon confertus), Blue Gum (Eucalyptus saligna) and Tallowwood (E. microcorys) with a rainforest subcanopy (Horton 1999b; NPWS 2002). In places this forest type abuts the subtropical (Floyd 1990) dominated by White Booyong (Argyrodendron trifoliatum). The Ripple-leaf Muttonwood may also occur in this vegetation community.
Richmond River Floodplain
The native vegetation of the Richmond River floodplain is a complex mosaic of alluvial subtropical and dry rainforest (lowland floodplain rainforest), swamp sclerophyll forests and tall woodland. The
Ripple-leaf Muttonwood is currently known to grow on the margins of lowland floodplain rainforest, where a rainforest subcanopy or understorey is maintained. The Endangered Ecological Community of Lowland Rainforest on Floodplain is part of the habitat of the Ripple-leaf Muttonwood.
Of the two populations of the Ripple-leaf Muttonwood that occur on floodplain areas, one is known to occur in open swamp sclerophyll forest dominated by Prickly Paperbark (Melaleuca stypheloides) (Horton 1999a). The other population occurs in rainforest containing Whalebone tree (Streblus brunonianus) in association with Sweet Myrtle (Austromyrtus fragrantissima) (Horton 1999a). This rainforest vegetation community merges with a community characterised by Pepperberry (Cryptocarya obovata), Dendrocnide exselsa, Ficus spp. and Hoop Pine (Araucaria cunninghamii), so it is likely that this also forms part of the habitat of the Ripple-leaf Muttonwood (Floyd 1990).
A more comprehensive list of the plant species currently associated with Ripple-leaf Muttonwood can be found in Appendix 2.
The Ripple-leaf Muttonwood is found in areas with high light levels (Horton 2000). This light regime is generally associated with open forest, forest margins or forest gaps but may also be associated with a regenerating forest. Forest gaps and margins are ephemeral. Over time, a denser forest canopy may develop and prevent Ripple-leaf Muttonwood from effectively flowering, this has been observed in individuals growing under a dense canopy (Horton 1999a).
The life history and ecology of the Ripple-leaf Muttonwood is largely unknown. The following information is based on limited field surveys and opportunistic field observations by botanists and DEC staff. Knowledge of other, apparently closely related, species of Rapanea that occur in NSW and south-east Queensland is also used to suggest how the plants may reproduce and disperse.
The Ripple-leaf Muttonwood appears to rely on both seed production and suckering for reproduction. The relative contributions of suckers and seedlings to reproduction in the wild are unknown.
The Ripple-leaf Muttonwood has been observed to sucker from the lateral roots of a parent plant. At the populations at Boatharbour and Mallanganee radiating lines of younger plants have been observed clustered around a larger plant (Reid pers.comm.).
Suckering has also been observed in other species of Rapanea, i.e. Brush Muttonwood (R. howittiana) (Horton 1999a) and Variable Muttonwood (R. variablis) (Floyd pers. comm.).
Flower and fruit production
Flowering in Ripple-leaf Muttonwood has been recorded as occurring from October to December, but the species probably flowers as early as September (Jackes pers. comm.). No systematic records of flowering phenology of the Ripple-leaf Muttonwood have been collected.
Horton (1999a) has speculated that the Ripple-leaf Muttonwood requires a relatively high light regime to trigger flowering. It has been observed in Brush Muttonwood populations that plants growing on forest edges flowered and fruited, while at the same time healthy mature trees under a forest canopy were not reproducing (Horton 1999a).
The period of fruit production of the Ripple-leaf Muttonwood is not well known. Fruit have been recorded in November (Jackes pers. comm.) and there is anecdotal evidence of fruit on a plant in early January 2000.
The pollination mechanisms of the Ripple-leaf Muttonwood are not understood. The species is probably insect-pollinated as it has small flowers in an inconspicuous inflorescence and others in the same genus are insect-pollinated.
Thrips pollinate both the Brush Muttonwood and Variable Muttonwood (Williams pers. comm.). However, these two species employ divergent breeding systems, the Brush Muttonwood being highly, and probably totally, self-incompatible, while the Variable Muttonwood is highly self-compatible.
Unfertilised flowers have been observed on Brush Muttonwood (Horton 1999a), suggesting that sometimes pollination does not occur.
The seed dispersal vectors of the Ripple-leaf Muttonwood are unknown. The fruit of the locally common Brush Muttonwood and Variable Muttonwood are eaten by Rose-crowned Fruit-doves (Ptilinopus regina) and Lewins Honeyeaters (Meliphaga lewinii) (Floyd 1989). The fruit of Ripple-leaf Muttonwood is blue as in other members of the genus and it occurs in the habitat of the aforementioned bird vectors, so it may be dispersed by similar means to those of other Muttonwoods.
Uneaten fruit are expected to fall and germinate near the parent plant and this would contribute to the clustered distribution.
Seed germination and seedling establishment
No information is currently available on seed viability or the conditions that favour germination of the Ripple-leaf Muttonwood. The growth rate of the Ripple-leaf Muttonwood is also unknown.
Ripple-leaf Muttonwood is known from an estimated 407 plants distributed across three populations. The number of genetically distinct plants is unknown but most probably substantially less than the total observed due to suckering.
Height and flowering observations can be used to derive an estimate of the number of mature individuals of Ripple-leaf Muttonwood. However some of the mature plants may be suckers. Anecdotal evidence of flowering in 2002 indicates there is at least one sexually mature plant in the Boatharbour population and three sexually mature plants in the Mallanganee population. There are at least 16 Ripple-leaf Muttonwood plants greater than 2 m high across all the known populations. It is therefore estimated that there are 4 to 16 mature individuals in the known population of Ripple-leaf Muttonwood.
The variety of height classes observed at the Mallanganee and Boatharbour populations (Horton 1999a, Horton 1999b) suggests that recruitment is occurring at these populations and this may include seedlings as well as suckers. This indicates that these populations have the potential to persist in their habitat.
The Ripple-leaf Muttonwood appears to be subject to direct competition from the weed Lantana (Lantana camara) as both species preferred habitat include wet forest margins in areas with fertile soil. A number of Ripple-leaf Muttonwood plants have been found under dense Lantana in Mallanganee National Park. The response of the Ripple-leaf Muttonwood to release from competition with Lantana is being monitored by the DEC as part of a bush regeneration program in Mallanganee National Park.
Native plants that have been observed in Ripple-leaf Muttonwood habitat and that have the potential to compete with Ripple-leaf Muttonwood are:
- Basket Grass (Oplismenus sp.)
- Cockspur (Maclura cochinchinensis),
- Slender Grape (Cayratia clematidea) and
- Water Vine/ Native Grape (Cissus antarctica).
As discussed previously, competition with other plant species for light may affect the ability of Ripple-leaf Muttonwood plants to flower (Horton 1999a). The dynamics of other forms of competition between Ripple-leaf Muttonwood and other native plant species is not known.
The ecological relationship between the Ripple-leaf Muttonwood and predators and parasites is unknown.
The Ripple-leaf Muttonwood appears to persist on the margins of forest types that are either fire intolerant or require a relatively long time between fire events. It is unknown whether the Ripple-leaf Muttonwood would survive a fire event.
Aboriginal people have inhabited the Richmond Range for many thousands of years and are likely to have traditionally used fire to promote new growth for grazing mammals and to keep corridors open for travel (NPWS 2002). Disturbance by fire may have a role in creating habitat suitable for the establishment of the Ripple-leaf Muttonwood.
Seasonal flooding, especially on a small scale is not uncommon in the Ripple-leaf Muttonwood habitat on the Richmond River floodplain. Inundations frequently occur in late summer and/or autumn, with rare flooding in winter and spring. The soil of Ripple-leaf Muttonwood habitat near Tatham is seasonally water-logged for some weeks after moderate rain. While the Ripple-leaf Muttonwood has been found to persist under these conditions it is difficult to determine whether flooding assists or inhibits the species.
The Tatham and Mallanganee populations of Ripple-leaf Muttonwood have been subjected to intermittent grazing by cattle in the past. While the Tatham population has remained suppressed with very low numbers, the Mallanganee population has clusters of many suckers around each parent plant. This may be attributed to different grazing regimes or other factors independent of grazing.
The response of the Ripple-leaf Muttonwood to grazing by other species is not known.
Habitat clearing and fragmentation are believed to be the primary causes of past decline in the Ripple-leaf Muttonwood. Although probably never common, the
species has declined to critical levels. The likelihood of the Ripple-leaf Muttonwood successfully repotential habitat is unknown at this stage. In-situ management of known populations and ecological research into the species are likely to prevent its extinction and promote recovery of the species, however, it is unlikely that the species will ever become common in the wild.