ListingMicrantheum Statement for Micrantheum serpentinum serpentinum (western tridentbush) western tridentbush T A S M A N I A N T H R E A T E N E D F L O R A L I S T I N G S T A T E M E N T Image by Rob Wiltshire Scientific name: Micrantheum serpentinum Orchard, Aspects of Tasmanian Botany: 60 (1991) Common Name: western tridentbush (Wapstra et al. 2005) Group: vascular plant, dicotyledon, family Euphorbiaceae Status: Threatened Species Protection Act 1995 : rare Environment Protection and Biodiversity Conservation Act 1999 : Not listed Distribution: Endemic: Tasmanian endemic Tasmanian NRM Regions: Cradle Coast Figure 1 . Distribution of Micrantheum serpentinum in Plate 1 . Micrantheum serpentinum with immature fruit Tasmania, showing NRM regions (image by Richard Schahinger) 1 Threatened Species Section – Department of Primary Industries, Parks, Water & Environment Listing Statement for Micrantheum serpentinum (western tridentbush) SUMMARY: Micrantheum serpentinum is a leaves, with the male flowers usually above the straggly shrub in the Euphorbiaceae (spurge) female flowers. Flowers have perianth segments family, restricted to ultramafics (Cambrian less than 2.5 mm long, and are usually flushed serpentinite) in Tasmania’s northwest. Habitat red in parts; the male flowers have six stamens includes open low eucalypt woodland, and a vestigial ovary, and the female flowers shrubland and heathland, generally on lateritic have three styles The fruit is an oval-shaped soils, in a region with mean annual rainfalls capsule 3 to 3.3 mm long, yellow-brown in exceeding 2000 mm. The main threat to the colour with the persistent purplish-black styles species is mineral exploration and extraction. at its apex; the capsule has three locules, each The prolonged absence of fire also poses a with two ovules. Seeds are glossy, pale, creamy- threat, with localised impacts due to weed brown, oblong to suborbicular, c. 2 mm long. infestations and the construction and (description from Orchard 1991) maintenance of roads and power easements. Confusing Species IDENTIFICATION AND ECOLOGY Micrantheum hexandrum is the only other species of Micrantheum in Tasmania . It is a shrub to 3 m Micrantheum serpentinum flowers from September tall growing in riparian habitats in Tasmania’s to early November, with fruit maturing by mid- northeast: the closest recorded occurrence to January (Orchard 1991). Pollinators are M. serpentinum is near Deloraine (a separation of unknown. Dispersal of seed occurs via c. 100 km). The leaves of M. hexandrum are explosive dehiscence from its fruit, with few entirely glabrous, are generally longer and seed likely to be dispersed more than a few narrower than those of M. serpentinum , and have metres from their parent plant (aside from an acute apex . Micrantheum serpentinum is strictly those on plants close to creeklines). The monoecious, whereas for M. hexandrum some longevity of seed is unknown. plants may bear male flowers only (Orchard The species is known to be capable of 1991). colonising disturbed areas, such as roadside verges and quarries; its response to fire is unknown. Survey techniques Surveys for Micrantheum serpentinum can be undertaken at any time of year due to species’ distinctive foliage. Description Micrantheum serpentinum is a much-branched, straggly shrub to 2 m tall. Its leaves occur in groups of three at alternately arranged nodes; they range in shape from oblong, narrowly Plate 2 . Micrantheum serpentinum habit ovate to narrowly obovate, are 5 to 9 mm long (image by Paul Black) and 1.5 to 3.3 mm wide, leathery, concave, dark sub-glossy green above and paler below, DISTRIBUTION AND HABITAT glabrous aside from minute hairs on the Micrantheum serpentinum is endemic to margins near the rounded apex (which is northwestern Tasmania (Figure 1). It is usually minutely apiculate or very minutely restricted to Cambrian ultramafics (Gibson et notched). Plants are monoecious, that is, al. 1992), with three main locations: Serpentine separate male and female flowers occur on the Hill and Serpentine Ridge (both in the vicinity same plant. The yellowish to greenish coloured of Renison Bell), and the Heazlewood River flowers occur singly in the axils of the upper area between Luina and Savage River. 2 Threatened Species Section – Department of Primary Industries, Parks, Water & Environment Listing Statement for Micrantheum serpentinum (western tridentbush) The species grows in shrubby open low POPULATION PARAMETERS eucalypt woodland dominated by Eucalyptus Micrantheum serpentinum is known in Tasmania nitida or Eucalyptus nebulosa (Gray 2008), from three subpopulations, as represented by shrubland or heathland, typically on rocky occurrences in three disjunct ultramafic regions: hillsides (Orchard 1991), but may also occur on Serpentine Hill, Serpentine Ridge and more poorly-drained sites (North et al. 1998). Heazlewood River (Table 1). The species has Associated species may include Acacia mucronata, been described as being ‘locally abundant’ and Allocasuarina zephyrea, Banksia marginata, Bauera ‘widespread’ within its ultramafic habitat rubioides, Gahnia grandis, Gymnoschoenus (Orchard 1991, North et al. 1998), though there sphaerocepahlus, Hakea epiglottis, Lepidosperma are few quantitative estimates for either plant elatius, Leptospermum glaucescens, Leptospermum numbers or area of occupancy. scoparium, Pultenaea juniperina, Sprengelia incarnata, Spyridium gunnii and Westringia rubiaefolia , with The area of ultramafics in the three regions has the EPBC-listed Epacris glabella present at all been estimated at 250 ha, 2700 ha and 3200 ha, three locations. Lateritic soils are associated respectively (Gibson et al. 1992). Perhaps half with the ultramafics at each location (Gibson et to two-thirds of this area represents potential al. 1992). habitat for Micrantheum serpentinum in the form The elevation range of known sites is 110 to of eucalypt woodland, scrub or heath — the 480 m above sea level, and the mean annual greater proportion of this area has yet to be rainfall is in excess of 2000 mm. The species’ surveyed in detail. recorded occurrences have a linear range of 47 km and extent of occurrence c. 230 km 2; reliable estimates of the area of occupancy are not available. Table 1. Populations of Micrantheum serpentinum in Tasmania Subpopulation Tenure NRM 1:25 000 Year last Area Number of region mapsheet (first) seen occupied mature (ha) plants 1 Serpentine Hill State Forest Cradle Coast Dundas 2012 10–15 10,000+ (1976) 2 Serpentine Ridge State Forest & Cradle Coast Rosebery 2012 unknown 10,000s? Meredith Range Parsons (1988) Regional Reserve 3a Heazlewood River Savage River Cradle Coast Waratah 1988 unknown unknown (Bronzite Hill) Regional Reserve (1988) 3b Heazlewood River State Forest Cradle Coast Waratah 1990 unknown unknown (Burgess Hill) (1990) 3c Heazlewood River State Forest & Cradle Coast Donaldson 2010 unknown unknown (Roaring Magg Savage River Savage River (1990) Creek – Gabbro Regional Reserve Hill – Brassey Hill) 3d Heazlewood River Heazlewood Cradle Coast Savage River 1995 unknown unknown (Duffs Hill – Conservation Area (1989) Heazlewood Hill) 3e Heazlewood River State Forest or Cradle Coast Savage River 1990s? roadside unknown (south-central) Savage River occurrence Regional Reserve 3f Heazlewood River State Forest or Cradle Coast Savage River 1990 roadside unknown (southwest) Savage River (1990) occurrence Regional Reserve Note: Species first collected in the Heazlewood River area in 1930 by H.F. Comber (Tasmanian Herbarium: HO 6315) 3 Threatened Species Section – Department of Primary Industries, Parks, Water & Environment Listing Statement for Micrantheum serpentinum (western tridentbush) New records for Micrantheum serpentinum since • 90% of mature individuals occur in 15 or its listing on the TSP Act in 1995 have mostly fewer subpopulations or locations and no been a result of surveys associated with mineral more than 5 of these occur in an area that is exploration. Surveys in the Serpentine Ridge free from sudden processes capable of area since 2007 have shown the species to be causing largely irreversible loss of more-or-less continuous over a distance of at individuals or habitat. least 6 km; c. 3000 plants were recorded in an area of about 0.4 in the far south, but other THREATS, LIMITING FACTORS AND records are generally qualitative in nature. Plant MANAGEMENT ISSUES numbers were estimated for part of the Serpentine Hill subpopulation in 2004, with a Mineral exploration and/or extraction: conservative estimate of 10,000 plants in 10 to Micrantheum serpentinum occurs exclusively on 15 ha area (data held by the Threatened Species ultramafic geology, substrates well known for Section). Anecdotal reports suggest comparable their mineral-prospectivity (Gibson et al. 1992). densities for at least parts of the Serpentine Areas supporting the species are in Ridge subpopulation, indicating a total consequence at risk from mineral exploration population in the tens of thousands, though in and extraction. Some known sites have already the absence of supporting data such a figure been affected by such activities, and others remains purely speculative. remain at risk directly (e.g. exploration roads, tailings dams, open-cut mines) or indirectly (e.g. It is considered likely that targeted surveys of introduction of weeds and disease, changes in potential habitat in the three main ultramafic hydrology). regions will result in ‘infilling’, while surveys of Regional Reserves are available for mineral