FRUIT DIVERSITY AND DISPERSAL IN SOLA NUM IN AUSTRALIA

The forms of fruits of the Australian species of Solanum are described and related to their dispersal agents. The succulent berry is the most common, but trample burrs, censer mechanism, capsules, hard and dry berries and a possible tumble weed have evolved. Birds are the most commonly recorded agent of dispersal but marsupials, wild dog, bats, man, wind and water are important. Introduction The genus Solanum, with about 90 species native to Australia, has evolved a range of fruits and dispersal mechanisms. The growth habits of the native species vary from annuals to small trees, the most common being herbaceous perennials or small to medium, colonial, short-lived shrubs. The fruits of Solanum are typically described as berries (pulpy indehiscent fruits with seeds embedded in the flesh) but several modifications have evolved and succulent berries, finally-dry bony fruits, trample burrs, capsules, censer mechanisms and several variations less easily classified may be found. This account has been influenced by the systematic account of dispersal by Van der Pij1 (1969) who discusses many aspects of the biology involved, and the agents responsible for dispersal and the syndromes rot plant characters ffidt May be associated with each. Classification of fruits into a single category is not always possible, particularly for succulent fruits produced close to the ground which may be taken by reptiles, birds or mammals. The types of fruits of Australian Solanum species and their likely means of dispersal are shown in Table I. Dispersal by reptiles: Saurochory The syndrome of fruit characters that Van der Pij1 associates with saurochory is that fruits may be coloured, have a smell and often borne near the ground or dropped at maturity. It is obviously not an exclusive group of characters and fruits with them are also likely to be distributed by birds and mammals. The large omnivorous skinks, e.g. Sleepy Lizard (Trachydosaurus rugosus), Blue Tongue (Tiliqua scincoides) and Spiny Skink (Egernia stokesii) are widespread across semiarid southern Australia. The first is known to be partial to cultivated strawberries and tomatoes and both Sleepy and Blue Tongue Lizards have been found in the vicinity of S.simile which has drab green (sometimes purplish), succulent, aromatic fruit which drops to the ground when ripe. Other species with similar fruits include S.opacum, S.vescum, S.cleistogamum, S.ellipticum, S.pungetium, S.prinophyllum. Species with coloured fruits that drop to the ground but which grow in mesic and/ or tropical sites are beyond the geographical range of these lizards. These species include S.discolor which has erect and prostrate growth forms and the taller S.macoorai, S.laciniatum and S.aviculare. The fruits of the last three species are known to be eaten by birds. Dispersal by birds : Ornithochory The fruit characters associated with dispersal by birds are:an attractive edible part when ripe, outer protection against premature eating and signal colours at maturity. There is less emphasis on aroma and strength of attachment, and no special placement on the plant. Neither reptiles nor birds (except Cockatoo) can usually cope with a hard rind.