Water and seeds

Fruits, Nuts, Seeds and other things
By Spencer Shaw
Rain, rain and more rain please!Well that’s what we where all saying just a month or so back and gee its good to have the old ‘gravity challenged’ H2O doing its stuff again.While on the subject of water have you ever pondered its ability to spread seed? Many stream and riverside plants use not only wildlife or wind but also flowing water to disperse their seed. Waterways have many advantages as agents of seed dispersal, the most obvious of course being that they are permanently moist! However we can also add relatively high levels of available nutrients to assist seedling growth, regular disturbance of floods creating ideal germination conditions i.e. River sheoak Casuarina cunnighamiana, leaching of chemicals that inhibit germination i.e. Water Gum Waterhousea floribunda and weathering of hard seed cases i.e. Blue quandong Elaeocarpus grandis. Last but not least we can add the ability of waterways to carry seed far from the parent tree to assist the colonization of new areas ‘to boldly go where no seed has gone before’.Creek Lillypilly-Syzygium smithii  (syn. Acmena) – fine leaf, is a classic example of plant that produces many more seed when close to water and the closer the better. Even on the same plant branches overhanging water are often dripping with fruit while those over dry land carry few. This can provide the seed collector with an uncomfortable challenge as the seed are produced in the depths of winter and standing up to your unmentionables in the chilly waters of the Obi on a winter’s morning makes even the deepest of baritones utter notes that could shatter glass! This form of Syzygium Smithii is very common in our wider, sunnier, and rocky stretches of rivers. It is amazingly flood resistant due to its small multi branched form and clings to the riverbank with roots of steel, while other plants are torn and washed away. And after the severe floods of summer have left the river banks scoured and bare, the Lillypilly seedlings spread by the river in winter and established during spring resprout from rocky crevices to make their mark in the riparian zone.Weeping Lillypilly -Syzygium floribunda takes over from the creek lillypilly downstream on the Blackall Range at altitudes of about 250 metres and below. An unusual feature of this tree is that it is one of the few native trees in our area that forms monocultures, although regular flooding make this habitat extremely hostile and only riverbank specialists like the Waterhousea can survive these extreme conditions. Riverbanks dominated Waterhousea can be extremely stable environments, their deep roots anchor them and their surface roots form a mat over the riverbank which in shallow streams can even cover the stream bed, the ultimate in erosion control. These guardians of our riverbanks are often bruised and battered and their trunks thick with suckers and regrowth and yet they require the river for their very survival. The fruit of Waterhousea need to fall into the river and require the flowing water of the river to leach chemicals out of the fruit that prevent germination. One way of simulating these conditions for the home propagator I’ve heard is to suspend a mesh bag of fruit in a toilet cistern and the regular change of water in the cistern leaches the chemicals away. I imagine however that those who prefer their porcelain to retain its pearly gleam shouldn’t try this.Giant water gum-Syzygium francisii is another member of the lillypilly group that thrives along our watercourses. It has developed a fruit that like styrofoam is as much air as solid matter. These fruit can float for at least a day and be carried far away from the parent tree by a flowing steam or river. The lucky ones may eventually be washed up on to the riverbank and given a chance to grow. This floatability of Syg. francisii can make them very easy to collect by the opportunistic seed collector with a small net, all you need to do is scoop the floating fruit from the waters surface. This can be a rather civilized occupation on a hot summer’s day, unlike the situation with the Acmena smithii. Next time you’re strolling along the riverbank give some thought to how the vegetation has helped to shape the river and how the plants themselves have in turn have been shaped by the river.