Description
Subterranean Cape sedge (Trianoptiles solitaria) is a small leafy annual tufted herb that grows to about 200 mm high. The leaves are grass-like, slightly fleshy, smooth, pale green. It has two kinds of spikelets and nuts (fruit/seed). The flower heads consist of a few small clusters of spikelets. These aerial spikelets have two flowers with both male and female parts; basal spikelets are hidden at the base of the stems and leaves, are larger, and have only female parts.
The nut that develops in aerial spikelets is about 2 mm long and has 3 feathery scales around it; each scale is mostly divided in the upper half into 3 lobes, the central one bristle-like. The nut in basal spikelets is larger and lacks scales.
For further information on and identification of Subterranean Cape Sedge contact the herbarium in your state or territory.
Distribution:
Subterranean cape sedge is only known from one site near Koonung Creek in a municipal reserve in North Balwyn, a suburb of Melbourne, Victoria. It is on a grassy slope that is a seepage area in winter, about 100 m from the creek, associated with a disturbed mixture of native and introduced species.
By 1999, it was estimated that there were more than 100,000 plants in an area about 200 x 50 m, with smaller outlying populations nearby. The infestation persists, but there is no evidence that it has spread into undisturbed areas or moved beyond the site.
This species could be a problem in regions of southern Australia with a Mediterranean climate (parts of Victoria, South Australia and Western Australia), extending as far north as southern New South Wales.
Habit:
(Subterranean Cape Sludge in Habitat.)
Herb
Key points:
Subterranean Cape Sedge (Trianoptiles solitaria) is a small annual sedge native to South Africa.
It is only known from one site in a reserve in a Melbourne suburb.
It has both aerial and basal spikelets and nuts with 3 feathery bristles.
This weed is a potential problem in southern Australian regions with a Mediterranean climate, as it can compete with small native species.
How it spreads:
Subterranean Cape Sedge is an annual that produces several nuts per tuft (and therefore many nuts annually in that large population), and dispersal would be by movement of nuts with soil and mud. Mowers and other vehicles are potential vectors. Nuts are likely to persist in the soil seedbank for a considerable period, as with many other sedges, but no longevity studies have been done on this species.
Where it grows:
In its native region, it grows in a mediterranean climate, in seasonally damp habitats. In its only known naturalised site in the Melbourne area, it grows on a steep slope with low herbaceous vegetation, dominated by Kikuyu Grass (Pennisetum clandestinum); a winter-moist habitat. Despite the dense grass, Subterranean Cape Sedge persists there.
Flower colour:
No flower
Distribution map:
Current distribution of Subterranean Cape Sludge
Impacts:
Subterranean Cape Sedge was placed on the Alert List for Environmental Weeds because of its ability to produce large quantities of long-lived seed (as a whole population: each plant only produces a few seeds) and ability to naturalise in Australia. Small, quick-growing annual species like this have the potential to crowd out native species in their early stages of growth.
Origin:
Subterranean Cape Sedge is native to the Cape Province of South Africa. The other two species in the genus are also found only in that Province. No species of Trianoptiles is native to Australia.
History:
Subterranean Cape Sedge was probably introduced accidentally, as nuts, but exactly how is not known. Being such an inconspicuous plant, it would not have been noticed for many years until the number of plants had built up considerably. It was first noticed in 1989 in a reserve in North Balwyn, Victoria.
