Part of the Evolution of Australian Biota Module Biology in Focus, Preliminary Course

Planet Earth and Its Environment A 5000-million year Journey

Part of the Evolution of Australian Biota ModuleBiology in Focus, Preliminary CourseGlenda Childrawi and Stephanie Hollis

Evolution of Australian BiotaTopic 10: Reproductive Adaptations in Plants: Seed Dispersal and Asexual ReproductionSeed DispersalAfter successful pollination and fertilisation of the flower, the seed develops. It is an advantage for a plant to spread or disperse its seeds over a wide distance. This prevents overcrowding and increases the chances of survival in situations of environmental change such as fire or disease.openwalls.com

Seed DispersalSeeds are dispersed by wind or animals such as insects, birds and mammals are designed to disperse in many ways. Australian native plants have evolved a variety of adaptations to aid in the effect and successful dispersal of their seeds. en.wikipedia.org

WindSome seeds are aerodynamically designed to be blown long distances by the wind. For example, Flindersia, leptospermums, melaleucas, native daises and casuarinas.tame.ifas.ufl.edu

AnimalOther seeds have structures, such as hooks or barbs, which cling or stick to the fur or feathers of animals. This is so they can be carried long distances before they fall to the ground. Examples include: Pisonia (birdlime tree) and Pittosporumsuperstock.com

davesgarden.comAnimalOther seeds are enclosed in bright coloured fleshy fruits. Red is a very conspicuous colour to birds, so any fruit or berries containing seeds are highly likely to be dispersed by birds (lilypillys). Smaller birds are also interested in purple berries such as tree violet (Hymenanthera dentate)southgippsland.wordpress.com

AnimalSeeds can pass through the digestive system of mammals or birds which unknowingly transport the seeds to new locations so that they germinate on the spot upon which they were defecated.burrard-lucas.com

AnimalSome seeds must pass through the gut of an animal to be able to germinate. For example the nitre bush (Nitraria billardieri) depends on emus to eat and spread their seeds. Another example is the mistletoe, it has sticky seeds which are deposited on trees by mistletoe birds.birdway.com.au

AnimalTo bribe ants, wattle (Acacia) seeds have some lipids attached to their outside. The seeds (like Lomandra and Grevillae) are carried by the ants to their nests where they consume the lipids but leave the hard seeds underground, safe from fire. Wattles can then flourish and grow after the hottest of bushfires.myrmecos.net

FireEucalypts, banksia and many other Australian plants store they seeds until fire destroys the branch or the entire plant. This allows the capsules to open, releasing the seeds for dispersal, usually by the wind.wombatwal.redbubble.com

FireThis provides a significant advantage to the seeds as the fire clears land areas and invites re-colonisation by new plants. The fastest dispersing and germinating plants can colonise more area of land.karencheng.com.au

FireNot all banksias and eucalypts store their seeds waiting for fire. Banksia integrifolia and Eucalyptus melanoxylon release their seeds once it is ripe. This is seen as a primitive feature compared with other species that are actually more suited to their environment and have more effective colonising mechanisms.northsydney.nsw.gov.au

WaterSome seeds rely on water dispersal, such as the water gum (Syzygium francisii) and the mangrove (Avicennia marina). Seeds may float small or large distances from the parent plant along rivers and estuaries or across seas.ecology.hku.hk

ExplosionFinally, some seeds are violently propelled from the base of fruit in an explosive discharge. Seeds are ejected from the pod at high speeds caused by the drying and contraction of the pod. Some seeds such as the Acacia cultriformis can be thrown up to 2 metres by this method.Hand out copy of Table 3.8 (Prelim Bio in Focus Text)dmt-nexus.me

Asexual ReproductionAsexual reproduction is the making of a new individual without the use of sex cells or gametes. Only one parent is required for the mitotic cell divisions to occur. sbi3uplantsjan2012.wikispaces.com

Asexual ReproductionSome types of asexual reproduction are:Binary fusionBudding (Hydra and coral)Spore formation (moss, fungi and ferns)Vegetation propagation (plant cuttings like roses)Regeneration (starfish and earthworms)Parthenogensis (Binoes gecko)treatyrepublic.netAsexual ReproductionPlants that reproduce asexually clone new individuals from portions of the root, stem, leaves or ovules of adult individuals. The asexually produced individuals are genetically identical to the parent. elateafrica.org

Vegetation ReproductionNew plant individuals are simply closed from parts of adults, such as runners, rhizomes and suckers. Runners are long, thin stems that grow along the surface of the soil. treatyrepublic.net

Vegetation ReproductionIn the cultivated strawberry, for example, leaves, flowers and roots are produced at every other node on the runner. Just beyond each second node, the tip of the node turns up and thickens, producing new roots and a new shoot that continues the runner.

gardenpool.orgVegetation ReproductionAnother example is spinifex grass which has long stems that grow horizontally along the surface of the soil. At each node, leaves and roots are produced that can be subdivided into new plants.treatyrepublic.net

Vegetation ReproductionRhizomes are underground horizontal stems that invade areas near the parent plant with each node being able to give rise to a new flowering shoot. Corms, bulbs and root tubers are stems specialised for storage and reproduction. The eyes or seed pieces of the potato give rise to the new plant. Rhizomes are characteristic of ginger, ferns such as bracken fern and many grasses.history-punk.com

Vegetation ReproductionThe roots of some plants produce suckers or sprouts, which give rise to new plants. Trees and shrubs that sucker, such as reeds, wattles and blackberries can spread quickly into a vacant patch of habitat after disturbance. flickr.com

BuddingBudding is one of the more unusual forms of asexual reproduction seen in plants. Budding involves the development of a new individual as an outgrowth of the parent plant. For example, Kalanchoe produces buds along leaf margins, which can break off and form new plants.

treatyrepublic.net

ApomixisIn certain plants, such as kangaroo grass, lemon and orange trees and dandelions, the embryos in the seeds may be produced asexually from the parent plant. The seeds produced in this way give rise to individuals that are genetically identical to their parents. anbg.gov.au

ApomixisBy reproducing asexually this way these plants also gain the advantage of seed dispersal, an adaptation usually associated only with sexual reproduction, as well as the rapid multiplication of plants.tki-health-om.blogspot.com

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