Life cycle stages

Most of our woodland plants have male organs (stamens and anthers with pollen) and female organs (stigma and ovaries) in the same flower (bisexual) on the same plant (monoecious). A few species produce separate male and female flowers (unisexual) on different plants (dioecious), e.g. Asperula conferta, Clematis glycinoides, Lomandra multiflora, Lomandra filiformis. In small populations of dioecious species where there are few or even no plants of one sex, there may be inadequate pollination and failure to set seed. For example in the woodland at the Australian Botanic Garden there is only a very small population of Lomandra multiflora.

Many plant families have very distinctive flower types - the family Fabaceae has pea-shaped flowers e.g. Lotus australis, while the grass and sedge families have specialised flowers that you might hardly recognise as flowers e.g. Scleria mackaviensis.

For most native woodland species flowering is not tied to particular seasons but is dependent on adequate rainfall and may happen at any time. This is in contrast to the plants in the Sandstone woodlands of coastal Sydney which have a distinctive peak of flowering in spring (September-October).

Unlike the colourful Banksias and Waratahs of the sandstone areas, most of the woodland flowers are small and not colourful. Flower colours are predominantly white, with some pink, purple or yellow. Colour and shape relate to pollination modes.

In contrast to the native species, many of the exotic weed species that are naturalised in the woodland have conspicuous and colourful flowers e.g. *Heliotropium amplexicaule, *Verbena rigida, *Hypericum perforatum, as many of these were introduced to Australia as garden plants, and have subsequently escaped from cultivation.

While we are used to seeing the flowers of most cultivated garden ornamental plants remaining open all day, there are different daily flower opening times for some of the woodland species. The flowers of some species remain open all day and under all conditions e.g. Bursaria spinosa, Pimelea spicata, Indigofera australis. Other species have flowers that are only open when it is sunny, and even then, for only part of the day e.g. Caesia parviflora and Wahlenbergia gracilis are open in the afternoons, Hypoxis hygrometrica and Tricoryne elatior are often open in the morning. On very hot days most flowers tend to wilt e.g. Ajuga australis.

Flowers of some species may last a few days, but others are only open for a day e.g. Caesia parviflora, although the plant may produce a succession of flowers. Flower availability is likely to be important in pollination, and presumably the period and time of opening relates to the presence of pollinators. However we know very little about the native pollinators of the woodland species.

Some plants do not produce flowers. Ferns produce spores which grow into prothalli on which the next generation embryo grows. Of the four fern species in the woodland, two are confined to moist habitats but the other two Cheilanthes sieberi and Cheilanthes distans grow in the dry woodland similarly to the other ground species.

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

Unlike the other life stages of plants, which occur mainly above ground, the seed is dispersed from the parent plant with adaptions to assist it to enter the below-ground soil seedbank. The woodland at the Australian Botanic Garden has no species that have plant-stored seedbanks (bradysporous or serotinous) like many of the sclerophyllous Banksia and Hakea species in the sandstone woodlands.

The enclosed protective nature of the seed, and its limited metabolic requirements, allows species to survive in the soil seedbank, avoiding unsuitable conditions such as drought, until moisture and temperature conditions are suitable for germination. How long seeds remain in the soil seedbank depends on moisture and temperature conditions, and the capacity of the seed to remain dormant. Persistence in the soil seedbank varies for different species.

Seed longevity ranges from about a year for some annual species to more than 20 years for some Acacia species. Some seed may be kept alive for much longer periods in artificial seed storage in the Australian PlantBank at the Australian Botanic Garden Mount Annan. However, such periods are unlikely to occur in natural conditions, where moisture and temperature conditions vary and soil seed predators are present.

In most woodland species the adult stage is probably longer-lived than the seed in the soil, but populations of short-lived ephemerals such as Ranunculus sessiliflorus and Daucus glochidiatus may appear as adults for 2-4 months followed by 1-3 years in the seed bank.

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

Populations are most vulnerable to change when adult plants die, particularly if a large number of individuals die at the same time. One of our particular interests has been to try to determine the potential lifespans of individual species. Our longevity estimates range from about 2 months for shortlived ephemeral species (e.g. Ranunculus sessiliflorus, Daucus glochidiatus, *Anagallis arvensis) to several hundred years for some long-lived trees and shrubs. General indications are that eucalypts may live up to 200 years, and judging by the size of some of our Narrow-leaved Ironbarks Eucalyptus crebra and Forest Red Gums Eucalyptus tereticornis, that some of these trees could pre-date European settlement. There is also a group of species that have indeterminate life spans, that is they keep growing indefinitely, assuming that conditions remain favourable. These plants include species that reproduce by bulbs and tubers such as the lilies e.g. Tricoryne elatior or spread by rhizomes e.g. Scutellaria humilis and root suckers e.g. Clerodendrum tomentosum. There are also some woody plants, in particular Bursaria spinosa, where the leaves and stems may be killed by fire but resprout from the base again and again. In the absence of death from debilitating environmental conditions, such as severe drought or disease, these plants appear to have the ability to live indefinitely. About half of the native species are relatively short-lived perennial species, that is living less than five years, though few of the native species (about 10%) are annuals with lifespans of less than one year. Indeed very few of these are true annuals in the sense that they come up reliably every year, annually. Rather they appear episodically from soil-stored seedbanks following specifically favourable conditions such as wet periods following drought, or in particular wet years, with gaps of perhaps 5-10 years when they are not evident. In contrast to the native species most of the exotic weed species are short-lived perennial species, with nearly half as annuals. However it is the few long-term perennial species, particularly *Olea europaea subsp. cuspidata, and indefinite perennial species *Hypericum perforatum, *Heliotropium amplexicaule and *Nassella neesiana, that cause the main ongoing weed problems in the Australian Botanic Gardens woodlands. Asterisk * indicates exotic species naturalised at the Australian Botanic Garden.

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