Asterolasia, a rare white star twinkling near a green town

It means nothing, but all three parts of the scientific name for this plant begin and end with an 'a'. Also appealing to my predilection towards gratuitous associations, the white-flowered subspecies of the otherwise yellow-flowered species grows near the green-named town of Emerald, in the Dandenong Ranges near Melbourne.

Asterolasia is a southern Australian genus in the citrus and boronia family, Rutaceae, with about 20 species. Its flowers are delicate and five-petalled; a little star-like. [Compared with otherwise similar genera like Phebalium, the outer layer of the flower - the calyx - is reduced and inconspicuous.]

Asterolasia asteriscophora is an uncommon species, found among rocks in forests from the north of New South Wales down to the Macedon Ranges in Victoria. The species name means 'starry carrier', a reference to the radiating branching of the tiny hairs all over the plant (clearly visible on the under-surface of the folded petal resting on the leaf below, and the leaf itself).

New South Wales has the one subspecies, asteriscophora, with yellow petals. Here in Victoria we have another subspecies, albiflora, a name which gives the game away: it has white flowers, or petals.

The more widespread subspecies in Victoria (and New South Wales) is called the Lemon Starbush, while the rare Emerald variant is sometimes called the Emerald Starbush here in Victoria - a little confusingly to those not familiar with the locality and expecting a flower colour hint. The name White Starbush does get official sanction in places like the Atlas of Living Australia, but do watch out for a spurious record in the west of Victoria on that site (this 1937 record from the Grampians is presumed to be incorrectly labelled).

We've been growing the Emerald Star Bush in the Cranbourne and Melbourne Gardens for a decade or so, trying to representatives of different genetic lines apart so if we need to replant at any time we have as much variety in the subspecies as possible.

Similarly in the Victorian Conservation Seedbank where we have a few different populations represented already and hope to get almost the whole range covered in time. We think the seed will last decades, maybe centuries, at minus 20 degrees, but as with all seed we need to test from time to time to make sure it remains viable.

Last time I asked (early last year) the Seedbank held 1,100 species, about a third of the Victorian native flora of c. 3,500 species. Most collections though are of uncommon species, so we have almost two-thirds of the 1,500 or so rare and threatened species in the State.

Asterolasia asteriscophora subspecies albiflora is one of those, an endangered species in Victoria, meaning it's under real threat of extinction. These days it only grows in a handful of populations near Emerald, mostly in heavily populated or semi-rural areas. In only one reserve is it found in reasonable numbers - otherwise it hangs on, often insecurely, in roadside remnants or on private property (thankfully a few 'convenanted' properties are established, or about to be established, near to Monbulk).

While seedlings germinate after some fires (they benefit from smoke stimulation), they appear to need at least a five-year gap between burns. In addition to ill-timed fires, loss and degradation of habitat puts pressure on these remaining populations, as do invasive native and exotic species.

The Emerald Starbush was given a scientific name, Eriostemon spathulifolius, back 1913 but omitted from subsequent floras as a minor flower-colour variant of Asterolasia asteriscophora. Following a detailed study of this species across its entire range (published in Muelleria, volume 16; 2002), Brian Mole recognised the Emerald populations as distinct but at subspecies level. It not only has distinctive white petals but various other attributes such as generally smaller leaves and flowers, and somewhat differently shaped leaves.

So even apart from its tautogramic (and matching posterior-tautogramic) scientific name - Asterolasia asteriscophora subspecies albiflora - the Emerald or White Starbush is a plant worth looking after.

Images: All taken from a single potted plant in the Melbourne Gardens nursery, on 12 October 2015, just past its flowering peak. Thanks to Neville Walsh for much of the information and some editorial checking, and to Rob Dabal, Conservation Officer with the Port Phillip and Westernport District for the latest on conservation efforts near Monbulk.