Carissa spinarum L.
(Apocynaceae – the oleander family)
synonyms: Carissa ovata, Carissa brownii, Carissa diffusa, Carissa edulis, Carissa opaca
common names: Currant Bush, Conkerberry, Burrum Bush
Carissa is the Latinized form of the Indian vernacular name for this genus; spinarum is Latin for ‘of thorns’. This species, due to the diversity of its form, has more synonyms than any other plant I know! I have listed the 5 most commonly met, but there are some 40 synonyms in the Carissa genus alone, and as well the plant has been placed in at least 9 other genera! The Scottish botanist Robert Brown (1773–1858), for example, described it under 4 different names; but Linnaeus had already described it as Carissa spinarum in 1771, and all subsequent names are treated as junior synonyms. Carissa ovata is still used extensively for the name of the plant in NSW, Queensland and the Northern Territory.
Carissa spinarum is most often found in semi-arid coastal areas of the tropical regions around the Indian Ocean, on fine-textured soils such as clays and clay-loams. In more arid regions it tends to be confined to areas of higher moisture such as at the base of hills, or in areas that flood; but it has a high ecological tolerance and can live in a wide range of habitats. In Australia, for instance, it is often found in association with Eucalyptus brownii (Box), Eucalyptus populnea (Poplar Box), Acacia cambagei (Gidgee) or Acacia harpophylla (Brigalow), in coastal rainforest, gallery forest and vine thickets in regions receiving more than 900 mm of rainfall annually, as well as in softwood scrubs and open eucalyptus savannah receiving less than 700 mm. The main distribution of the plant in Australia is along the east coast from Cairns to north-eastern NSW, with a disjunct population in the Kimberley region of Western Australia.
This is a sprawling native shrub with thorny stems. It can reach 3 m high, but is more usually between 1 and 2 m tall. The plant photographed is much smaller, due to its precarious hold on life by a boulder near the side of the road to the old Arcadia jetty. The plants branch out to cover an area more-or-less equal to their height, and, given suitable conditions, form dense, low thickets.
It has opposite leathery leaves, 2–4 cm long, either narrow or oval-shaped. The flowers are small and white, tube-shaped with pointed lobes at the end, and are highly scented. Oval-shaped berries follow. These are 5–10 mm long, sometimes even larger, becoming soft and black or dark purple when mature, and each contains 1 or 2 seeds. The fruits are edible, but only when fully ripe – before then they are poisonous. The berries have a sweet flavour, and were a popular food for the indigenous peoples, particularly in central Australia. The milky sap of this plant, as well as the unripe fruit, is poisonous.
Although the plant is not a declared pest under Queensland legislation, and is sometimes seen as a useful browse plant for stock, it is capable of reducing pasture production when infestations occur over a large area. It is drought-tolerant, and not grazed as readily as pasture species, giving it an advantage in dry times or in over-grazed situations. In many places it helps to reduce soil erosion, and it offers good habitats for birds and small wild animals.
Parts of the plant are used medicinally for joint and muscle pain by the Maasai people of Kenya and Tanzania.
Photographs taken in Geoffrey Bay 2010, 2013