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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3.30 plectranthus torrenticola P.I. Forst.

3.30.1 Summary

Plectranthus torrenticola is restricted to south east Queensland where it occurs from Kenilworth to Bli Bli. The distribution of P. torrenticola has a range of approximately 35 km and encompasses an area of occurrence of approximately 500 km². It is recorded from SF 1239 (Fty 1255), SF 918 (Fty 678) and from Kondallila National Park. There is no quantitative data on population sizes. A current threat to the Kondallila National Park population is considered to be habitat disturbance from pedestrian traffic.

3.30.2 Species description and identification

The 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 torrenticola was formally described in 1992 from material collected in State Forests, approximately 15 km north west of Nambour (Forster 1992). The botanical description of Plectranthus torrenticola is as follows:
Subshrub to 30 cm high, foliage slightly aromatic. Stems or lateral branches erect to straggling, the lower parts woody and up to 5 mm thick; upper parts with dense, retrorse, 5-8-celled non-glandular silver trichomes to 0.4 mm long, lacking glandular trichomes and sessile glands. Leaves discolorous; petiole 8-18 mm long; lamina narrow ovate, 20-60 mm long, 20-50 mm wide, fleshy, serrate with 10-16 teeth on each margin; both surfaces with sparse to dense, retrorse, 4-8-celled glandular and non-glandular hairs silver hairs, lacking sessile glands. Flowers in compact cymose clusters, arranged into terminal racemes 20-30 cm long. Clusters 10-12-flowered; pedicels 3-5 mm long. Calyx 1.8-2.1 mm long. Corolla 9.8-12.2 mm long, light -purple; tube 5.3-6.0 mm long, abruptly curved at an angle of c. 30° 2.1-2.2 mm from base, glabrous; upper lobes subcircular, 1.7-2.1 mm long, 1.9-2.2 mm wide; lateral lobes broadly-ovate, 0.9-1.1 mm long, 0.9-1.0 mm wide; lower lobe, oblong, 4.6-5.6 mm long, 2.7-4.5 mm wide. Fruiting calyx 5.4-6.0 mm long; lobes longer than or equal to tube. Seeds semi-spherical, c. 0.8 mm long, 0.8 mm wide, 0.5 mm thick, brown (Forster 1992). For a more detailed description and illustration refer to Forster (1992).
Plectranthus torrenticola is superficially similar to P. argentatus and P. omissus but differs from them by a number of characters that are set out in Table 3.30.1.
Table 3.30.1. Characters distinguishing Plectranthus torrenticola, Plectranthus argentatus and Plectranthus omissus

Character	P. torrenticola	P. argentatus	P. omissus
4-celled sessile glands	absent	present	present
flower number/cluster	10-12	6-10	14-16
corolla tube angle (°)	30	0-10	110-130
trichomes on corolla tube	absent	absent	present
corolla upper lobe size (length x width mm)	1.7-2.1 x 1.9-2.2	1.4-1.5 x 1.5-1.7	2.4-2.5 x 2.4-2.5
corolla lower lobe size (length x width mm)	4.6-5.6 x 2.7-4.5	4-4.2 x 4-4.2	4.4-4.5 x 3-3.2

3.30.3 Current conservation status

Plectranthus torrenticola is presently listed on the schedule of the Queensland Nature Conservation Act 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).

3.30.4 Distribution and abundance

P. torrenticola was not surveyed during the present study. Details from Queensland Herbarium specimens of P. torrenticola are listed in Appendix 1.29. Plectranthus torrenticola is restricted to south east Queensland where it occurs between Kenilworth and Bli Bli. A total of eight collections have been made. There are currently four known sites, including two within State Forest (SF 918 Fty 678, SF 1239 Fty 1255) and one in Kondallila Falls National Park. Another site is Dunethin Rock near Bli Bli. There is no quantitative information available on population sizes. The information on one specimen (AQ 565525) indicates that P. torrenticola was a frequent species on the rock outcrops in the vicinity of the collection site in SF 1239. The distribution of P. torrenticola has a range of approximately 35 km and encompasses an area of occurrence of approximately 500 km².

3.30.5 Habitat

P. torrenticola has been recorded growing on rocky outcrops on hillslopes or along edges of creeks in open eucalypt forest and on the margin of rainforest at altitudes of 250 to 450 m. The soils are shallow. In adjoining dry sclerophyll forest communities the common dominant trees are Eucalyptus pilularis, E. grandis, E. propinqua and Lophostemon confertus.

3.30.6 Life history and ecology

There have been no studies into the biology or autecology of Plectranthus torrenticola. P. torrenticola is a herbaceous shrub with an unknown life span. It is not known to be cultivated. The main method of reproduction is by sexually produced seeds. P. torrenticola as with most other Plectranthus 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.).

P. torrenticola has been recorded flowering between February and April. The pollinators of P. torrenticola 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 comprises 4 (1-seeded) nutlets which fall from the fruit after maturity. There is no available on seed viability and germination of this species.

3.30.7 Threats

The lack of information about present populations levels of P. torrenticola and precise habitat requirements makes it difficult to assess threats to this species. P. torrenticola is reported to be threatened by disturbance caused by visitation at Kondallila Falls National Park (Forster 1992).

3.30.8 Management, research and conservation measures

Very little is known about this species. Previously recorded sites should be examined to establish population sizes and extent. Areas of likely habitat in the vicinity of known populations should be searched for further occurrences. Observations should be made on potential threatening processes.

Locations of recorded populations should be brought to the attention of reserve managers. Attempts should be made to minimise the impact of pedestrian traffic on the population at Kondallila Falls National Park.

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