Hovea purpurea, State Herbarium of South Australia specimen AD96413149

A Remarkable occurrence

The Plant of the Month for May, Hovea purpurea, alpine hovea or rusty pods (formerly known as H. longifolia & H. beckleri), is an attractive violet-flowered shrubby pea with a disjunct outlying occurrence in the State that is truly remarkable.

Alpine hovea has its principal occurrences in eastern NSW and north-eastern Victoria (see AVH map) but re-appears over 1000 km to west on a few of the taller peaks in the Southern Flinders Ranges, which provide a refuge of cooler and moister conditions. The largest population here occurs on the rocky slopes of Mt Remarkable in DEWNR‘s Park of the Month for May 2016: Mt Remarkable National Park.

As well as Mt Remarkable and its northerly extension, the species occurs on the upper slopes of Mt Brown, The Dutchman’s Stern and Mt Aleck (in the Elder Range). There is also a Tate herbarium collection from the Gladstone area (probably from the late 19th century) and a single collection made in 1960 from St Mary’s Peak on the rim of Wilpena Pound. It would be good to have confirmation for these locations on the southern and northern extremes of its SA range, but the absence of recent records for such a striking plant suggests that it is no longer extant there.

Hovea purpurea specimen, detail with flowers

Being restricted to such a small zone on only the highest peaks of the southern Flinders Ranges, alpine hovea in SA is likely to be highly susceptible to climate change: there is no higher zone that it can shift up to as conditions become progressively warmer and drier.

The AD herbarium specimen shown here illustrates the species’ erect habit and distinctive leathery leaves that are smooth above and rusty-velvet below. It was collected by H.M. Cooper on Mt Remarkable in 1963 and still retains much of the original flower colour 53 years on.

H.M. Cooper (1886-1970) worked as an anthropologist with the South Australian Museum and, like many people of his time, had wide-ranging interests in natural history. Cooper contributed thousands of items, mainly aboriginal stone artefacts to the Museum’s collection, but also made important collections of fish, insects, land snails and plants. The latter collections are represented by over 3680 records in the State Herbarium database.

Hovea purpurea is listed as a Rare species in SA under Schedule 9 of the National Parks and Wildlife Act. Although its range is localised, alpine hovea is a prominent plant on the upper slopes of Mt Remarkable and hard to overlook when it is flowering in early spring.

Hovea purpurea, flowers & immature fruit, Mt Remarkable National Park. Photo: SA Seed Conservation Centre.

The State Herbarium has chosen Choretrum glomeratum R. Br. (common sour bush), as Plant of the Month for April 2016. It is found across southern South Australia and in Lincoln National Park, the Department of Environment, Water and Natural Resources‘ Park of the Month.

Type specimen of Choretrum glomeratum, collected by Robert Brown (Natural History Museum, London)

Choretrum glomeratum was first collected at Memory Cove by Robert Brown, between the 22–25 of February 1802. This became the type collection of the species and was made just after Matthew Flinders’ voyage had lost a cutter and its crew. This collection was later illustrated by Ferdinand Bauer for Endlicher‘s Iconographia generum plantarum (plate 45). Acacia alcockii was also collected at the same time and was annotated by Brown as “Mimosa no. 2”, but this collection did not become a type and was later mistakenly identified as Acacia retinodes.

The botanical legacy of Flinders’ expedition is discussed in detail in this article (28MB PDF) by State Herbarium Hon. Research Associate Robyn Barker.

Choretrum glomeratum grows into a many stemmed shrub 1–2 m high. Its erect branches with winged leaf bases and small leaves up to 3 mm long have a distinct pale yellow/green colour. The small white flowers occur throughout the year but are most obvious in late summer and autumn, fruit is a round ridged fleshy drupe that would probably benefit from passage through a gut for germination.

Choretrum glomeratum, branch with flowers & fruits and close-up of flower (Photo: SA Seed Conservation Centre)

A member of Santalaceae (3.6MB Flora of South Australia PDF), the 7 species of Choretrum restricted to Australia are parasitic on the roots of other plants, much like the better known quondong (Santalum acuminatum), sandalwood (Santalum spicatum) and native cherry (Exocarpos cupressiformis).

Choretrum glomeratum and some of its close relatives are part of a fascinating interaction between Camponotus ants (see Guide to Camponotus ants of Australia published by the SA Museum) and Ogyris otanes butterflies. Chewed branch ends on the shrub indicate the presence of the butterfly’s caterpillars that live in the ant’s nest and are escorted to and from the plant by the ants. Similar associations also occur with this group of blue butterflies and ants on mistletoes. The decline of plant numbers through habitat fragmentation and inappropriate fire regimes also impacts the butterfly population.