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Germination

Germination is the process by which the seed develops into a seedling. With adequate soil moisture, some species, will produce 100% germination immediately e.g. Brunoniella australisSolenogyne bellioides. Freshly collected seed of these species have no dormancy mechanisms. Other species have timing mechanisms that allow them to germinate at a particular time of the year that is most suitable for establishment. Dormancy mechanisms ensure that seeds do not germinate until the right conditions are met.

Dormancy mechanisms

Types of dormancy include physical dormancy where species with hard-coated seeds e.g. Convolvulus angustissimus, Dodonaea viscosa require physical breaking of the seed coat before germination (generally by fire). Seeds of the legume family Fabaceae, peas and wattles, e.g. Zornia dyctiocarpa, are also good examples.

Morphological dormancy is where the embryo needs to develop within the seed coat before the seed will germinate e.g. Bursaria spinosa.

Physiological dormancy is where the embryo is fully grown at seed maturity but specific conditions are required before germination occurs e.g. require fluctuating temperatures.

A wet period within a soil temperature range of 5-20ºC provides the final germination trigger for many species. Within this range, cooler season germinating species may be Ranunculus sessiliflorusDaucus glochidiatusCotula australis, *Stellaria media, *Anagallis arvensisTrifolium species. Warmer season species may include Dichondra repens, *Sida rhombifolia. Species germinating over a wide range of temperatures include Geranium homeanum, *Plantago lanceolata.

Many species require light for germination, particularly species that recruit into disturbed sites, e.g. Crassula sieberianaDaucus glochidiatusEinadia nutans subsp linifoliaEinadia trigonosPlectranthus parviflorusCalotis lappaceusCentipeda minimaWahlenbergia stricta.

Asterisk * indicates exotic species naturalised at the Australian Botanic Garden.

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