Calystegia affinis – critically endangered species listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the twining plant Calystegia affinis Endl. as a CRITICALLY ENDANGERED SPECIES in Part 1 of Schedule 1A of the Act, and as a consequence, to omit reference to Calystegia affinis Endl. from Part 1 of Schedule 1 (Endangered Species) of the Act. Listing of Critically Endangered species is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. Calystegia affinis (family Convolvulaceae) is described by Green P.S. (1994) as: “Vine, climbing or creeping. Leaves with petiole 5-12 cm long; lamina sagittate with a broad sinus and short triangular lobe each side near base, 4-9 cm long, 3.5-7 cm broad, attenuate onto petiole, acute to slightly acuminate, mucronulate. Flower solitary; pedicel 4-13 cm long; bracts broadly ovate to suborbicular, 1.2-1.5 cm long, cordate. Sepals ovate, 5 mm long, mucronulate. Corolla shortly funnel-shaped, 2.5-3.5 cm long, scarcely lobed, pink with 5 creamy longitudinal bands. Fruit unknown.”

2. Calystegia affinis is endemic to Lord Howe Island in NSW and Norfolk Island. Green (1994) suggests the Lord Howe Island population may be a separate subspecies as the flower is larger and the leaves broader than the Norfolk Island population.  C. affinis is listed nationally as Critically Endangered under the  Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (TSSC 2003).

3. Calystegia affinis was thought to be extinct on Lord Howe Island by Pickard (1983). He noted that it had only been collected twice (before 1875 and in 1936). In 1985, P.S. Green re-located the species at one site. More recent surveys targeting this species (Hutton 2001, 2005; S. Bower in  litt. Oct 2011) have found that  C. affinis is known only from fewer than 10 localities on Lord Howe Island, one of which (Old Settlement) is adjacent to the settlement area in the north of the island, while the others are in the southern mountains. All known sites occur within the Permanent Park Preserve on Lord Howe Island.

4. Calystegia affinis is likely to be a clonal species (Hutton et al. 2008), like a number of other  Calystegia spp. (Ushimaru & Kikuzawa 1999). Successful fruit production has not been recorded from the Old Settlement site, although developing fruits have occasionally been seen. These are thought to have been eaten by rats or birds prior to maturation (I. Hutton pers. comm. Oct 2011). S. Bower (in  litt. Oct 2011) suggests populations in the southern mountains of Lord Howe Island appear to respond opportunistically to disturbance and persist through soil seed banks and regrowth from underground root and stem structures. Fruit production and seedling recruitment have been observed in the field at three of the southern sites (S. Bower in  litt. Oct 2011). All plants in the southern mountains have white flowers rather than the pink flowers which are known from the  C. affinis site located at Old Settlement in the island’s north.

5. The geographic distribution of Calystegia affinis is estimated to be very highly restricted. The extent of occurrence, based on a minimum convex polygon enclosing all mapped occurrences of the species, the method of assessment recommended by IUCN (2010), is estimated to be 16 km2 . The area of occupancy is also estimated to be 16 km2 , based on a 2 x 2 km grid cells, the scale recommended for assessing area of occupancy by IUCN (2010).

6. It is difficult to estimate the number of individual plants of Calystegia affinis as it is likely to be clonal. Each location is thought to contain one to a few mature individuals, with a total population of between 25 and 40 plants on Lord Howe Island (S. Bower in  litt. Oct 2011). Hence, the total number of mature individuals is estimated to be extremely low.

7. The main threats to the species are competition and invasion of habitat by introduced weeds, particularly Pennisetum clandestinum (Kikuyu),  Stenotaphrum secundatum (Buffalo grass) and  Ageratina adenophora (Crofton weed) (DECC 2007; Hutton  et al. 2008; S Bower  in litt. Oct 2011). The Old Settlement site is overgrown by Kikuyu and Buffalo grass. Some control attempts have been made to minimise the impacts of these exotic grasses (Hutton  et al. 2008), but ongoing management of weed threats is required. Crofton weed is a problem at the sites in the southern mountains, with some individuals overgrown by this weed. “Crofton readily outcompetes native plant regeneration in these localities. However, Calystegia appears to be able to persist by its scrambling and adventitious habit. Climbers up to 4m tall were recorded, scrambling up into adjacent vegetation” (S. Bower  in litt, Oct 2011). Other weeds occurring at known sites include  Vicia sativa,  Duchesnia indica,  Verbena bonariensis,  Paspalum sp.,  Gnaphalium sp. (Hutton 2001, 2005; Hutton  et al. 2008; DECC 2007). “Invasion of native plant communities by exotic perennial grasses” and “Loss and degradation of native plant and animal habitat by invasion of escaped garden plants, including aquatic plants” are listed as Key Threatening Processes under the  Threatened Species Conservation Act 1995.  C. affinis is also threatened by demographic and environmental stochasticity due to its small population size.

8. Calystegia affinis Endl. is eligible to be listed as a Critically Endangered species as, in the opinion of the Scientific Committee, it is facing an extremely high risk of extinction in New South Wales in the immediate future as determined in accordance with the following criteria as prescribed by the  Threatened Species Conservation Regulation 2010:

Clause 7 Restricted geographic distribution and other conditions

The geographic distribution of the species is estimated or inferred to be:

(a) very highly restricted,

and

(d) a projected or continuing decline is observed, estimated or inferred in either of the key indicators:

(a) an index of abundance appropriate to the taxon, or
(b) the geographic distribution, habitat quality or diversity, or genetic diversity of the species.

Clause 8 Low numbers of mature individuals of species and other conditions

The estimated total number of mature individuals of the species is:

(a) very low,

and

(d) a projected or continuing decline is observed, estimated or inferred in either of the key indicators:

(a) an index of abundance appropriate to the taxon, or
(b) the geographic distribution, habitat quality or diversity, or genetic diversity of the species.

Clause 9 Low number of mature individuals of species

The total number of mature individuals of the species is observed, estimated or inferred to be:

(a) extremely low.

Associate Professor Michelle Leishman
Chairperson
Scientific Committee

Gazetted 16/11/12

References:

DECC (2007) Lord Howe Island Biodiversity Management Plan. Department of Environment and Climate Change 2007. Sydney.

Green PS (1994) Flora of Australia Vol. 49 Oceanic Islands 1. (Australian Government Printing Service: Canberra).

Hutton I (2001) Surveys of rare plants on Lord Howe Island - June 2001. Report to NSW Scientific Committee.

Hutton I (2005) Rare plants survey 2- Lord Howe Island. Report to Department of Environment and Conservation NSW.

Hutton I, Coenraads R, Auld TD, Denham AJ, Ooi MKJ, Brown D (2008) Herbicide impacts on exotic grasses and a population of the critically endangered herb Calystegia affinis (Convolvulaceae) on Lord Howe Island.  Cunninghamia 10, 539-545.

IUCN Standards and Petitions Subcommittee (2010) ‘Guidelines for Using the IUCN Red List Categories and Criteria Version 8.1.’ Prepared by the Standards and Petitions Subcommittee in March 2010.

Pickard J (1983) Rare or threatened vascular plants of Lord Howe Island. Biological Conservation 27, 125-139.

TSSC (2003) Threatened Species Scientific Committee, Commonwealth Listing Advice for Norfolk Island Flora - 11 Critically Endangered Species.

Ushimaru A, Kikuzawa K (1999) Variation of breeding system, floral rewards, and reproductive success in clonal Calystegia species (Convolvulaceae).  American Journal of Botany 86, 436–446.