Survey of threatened plant species in South East Queensland biogeographical region queensland cra/rfa steering committee survey of threatened plant species in
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3.28 plectranthus nitidus P.I. Forst.3.28.1 SummaryPlectranthus nitidus is restricted to south-eastern Queensland and north-eastern New South Wales, from the Nightcap Range north to the McPherson Range. There are two records in Queensland with one site possibly conserved in Springbrook National Park near the Mudgeeraba - Springbrook road. The other record is from the Land Warfare Centre near Canungra. There is no information on population sizes at these sites. Potential threats to the survival of the species at the Springbrook location include roadside clearing, invasion of habitat by weeds and fire. 3.28.2 Species description and identificationThe genus Plectranthus is placed in the mint family (Lamiaceae). Plectranthus is widespread throughout the tropical regions of Africa to Asia and Australia with approximately 200 species (Mabberley 1997). In Australia it comprises approximately 40 species of herbs and herbaceous shrubs. Plectranthus nitidus was formally described in 1992 from cultivated material collected from the upper reaches of Terania Creek in the Nightcap Range, New South Wales, approximately 30 km north of Lismore (Forster 1992). The botanical description of Plectranthus nitidus is as follows: Herb to 40 cm high, foliage scentless. Stems or lateral branches erect to straggling, the lower parts fleshy and up to 8 mm thick; upper parts with scattered, antrorse, 2-4-celled non-glandular trichomes up to 0.1 mm long, lacking glandular trichomes and sessile glands. Leaves discolorous; petiole 11-30 mm long; lamina lanceolate-ovate, 25-55 mm long, 15-30 mm wide, fleshy, serrate with 6-8 teeth on each margin; upper surface green, glabrous, veins impressed; lower surface purple, veins raised, with scattered, antrorse, 2-4-celled non-glandular hairs to 0.1 mm long, lacking glandular trichomes, with very scattered 8-celled sessile glands. Flowers in compact cymose clusters, arranged into terminal racemes 20-40 cm long. Clusters 6-10 flowered; pedicels 4.0-6.3 mm long. Calyx 2.5-2.7 mm long. Corolla 8-9 mm long, lilac-white; tube 3.8-4.4 mm long, abruptly curved at an angle of 25-30° 1.5-1.7 mm from base, glabrous; upper lobes subcircular, 2.2-2.5 mm long, 2.0-2.2 mm wide; lateral lobes oblong, 1.5-1.8 mm long, 0.8-1.0 mm wide; lower lobe oblong, 3.5-3.9 mm long, 2.3-3.1 mm wide. Fruiting calyx 3.6-3.8 mm long; upper lobe ovate, 1.8-2.8 mm long, 1.3-2.6 mm wide; lateral lobes lanceolate-falcate, 1.5-2.2 mm long, 0.7-0.9 mm wide; lower lobes lanceolate-falcate, 2.2-3.1 mm long, 0.6-0.8 mm wide. Seeds hemi-spherical, shiny black, 0.9-1 mm long, 0.5-0.8 mm wide, 0.3-0.4 mm thick (Forster 1992). For a more detailed description and illustrations, refer to Forster (1992). Plectranthus nitidus is related to P. apreptus from north Queensland but differs from this species in its stems, leaves and racemes lacking glandular hairs and nearly always lacking sessile glands; the axis bracts lanceolate-triangular and 3.6-3.8 mm long; and the corolla tube bent at 25-30°, 1.5-1.7 mm from the base. It is distinguishable from other species of Plectranthus in south east Queensland by its stems, branches, floral axes and the lower surface of the leaves having antrorse, non-glandular hairs. 3.28.3 Current conservation statusPlectranthus nitidus is presently listed on the schedule of the Queensland Nature Conservation 1992 as “endangered wildlife”. It is also listed on Schedule 1 Part 1 (endangered) of the Commonwealth Endangered Species Protection Act 1992. The species has not been assigned a national conservation status by ANZECC (1993). 3.28.4 Distribution and abundanceP. nitidus is restricted to south-eastern Queensland and north-eastern New South Wales where it occurs from the Nightcap Range north to the McPherson Range. It has a distribution range of approximately 60 km. P. nitidus was not surveyed during the present study. Details from Queensland Herbarium specimens of P. nitidus are listed in Appendix 1.27. There is a single record in Queensland from near the Mudgeeraba - Springbrook road. This site appears to be within Springbrook National Park but this needs to be confirmed. Recently, a second record for Queensland has been found at the Land Warfare Centre near Canungra. There is no information available on population sizes of this species in Queensland. 3.28.5 HabitatP. nitidus has been reported growing on damp rocks on cliff faces and rocky outcrops in subtropical rainforest or bordering subtropical rainforest. Recorded at 180 m above sea level. 3.28.6 Life history and ecologyThere have been no studies into the biology or autecology of Plectranthus nitidus. P. nitidus is a herb with an unknown life span. It is easily propagated by cuttings. The main method of reproduction is by sexually produced seeds. P. nitidus as with most other Plectranthus spp. produces roots from branch nodes where the branches come in contact with the soil surface. It is believed that the plants are fire-sensitive (P. Forster pers. comm.). The continued existence of this species after fire would rely on successful seedling recruitment. P. nitidus has been recorded flowering in February. The pollinators of P. nitidus are unknown. Pollinators reported for the family Lamiaceae include bees, birds, flies, wasps, butterflies and hawkmoths(Huck 1992). The most common pollinators for Plectranthus are bees and flies (Huck 1992). Fruits develop and mature soon after flowering. The fruit comprise 4 (1-seeded) nutlets which fall from the fruit after maturity. There is no information about seed viability and germination. 3.28.7 ThreatsThe site along the Mudgeeraba - Springbrook road may be subject to roadside clearing as part of road maintenance. Another potential threat to the species is habitat invasion by exotic species, particularly lantana (Lantana camara), mist flower (Ageratina riparia) and Crofton weed (Ageratina adenophora). The species is suspected to be fire-sensitive and incapable of regenerating from underground organs. The continued existence of the species in the wild after a fire would require the regeneration of the species from seed (obligate seeder). If fires were at a frequency that did not allow the production of adequate seed for future recruitment events then the population would decline and the species would be eliminated from the area. This is a potential threat at all sites. However, the habitat in which the species has been observed provides some degree of protection from frequent burning in that the rocky outcrops may buffer plants from fires. 3.28.8 Management, research and conservation measuresVery little is known about this species. Previously recorded sites should be examined to establish the population sizes and extent. Areas of likely habitat in the vicinity of the known populations should be searched for further occurrences. Observations should be made on potential threatening processes. The spread of weeds, the impact of fire and the condition of habitat on the rock faces should be monitored. Relevant management bodies should be made aware of population localities. |