How to use Flowers Characteristics in  the Identification of Australian  Tree Species

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Using Flowers Characteristics in Identification of Australian Tree Species

Introduction: Flowers are very useful in identification of native Australian shrubs and trees but are normally not the primary method (with exceptions) when identifying native species in their natural environment. Reasons for this are; the short term life span of flowers, being out of reach for closer inspection (i.e. flowers are held in the higher canopy), being rather inconspicuous and that species may not flower every year or commence flowering only as adult trees. An advantage of using flowers in classification is that species of the same genus will bear a very similar inflorescence. Using detailed illustrations, pictures and a comprehensive language the anatomy and arrangement of flowers (botanical; inflorescence) is explained on our web page below. Updated and extended November 2016.
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Flower Anatomy, Parts of a Flower

Flower Anatomy

Sepals: Appendages forming the base of a flower, which can be totally separated or fused together with free standing protrusions at the apex. The shape of sepals can vary from leaf-like structure resembling petals to tentacle shaped extensions as for the Tall Nightshade Solanum nobile (shown above).

Calyx: All sepals separated or fused together make up the calyx. The calyx plays an interesting part in identification, as some tree species retain it to the stage of mature fruit and beyond. The Hairy Lollybush Clerodendrum tomentosum (see page 7) retains the calyx at the base of the fruit, whereas species of the genus Syzygium (see page 10) at the top end of the fruit.

Pedicel: An individual flower stalk in a compound flower arrangement (Inflorescence).
Peduncle: The main flowering stem supporting the rachis to which individual stalks (pedicels) are attached to, or the stem of a solitary flower.
Petals: Petals are often brightly coloured or white components of a flower surrounding the ovary. All petals as a unit are called a corolla. The number of petals can vary from none to numerous. Petals have no reproductive functions.
Stamen: Stamens are the male reproductive parts of a flower. A stamen is made up of the anther (the swollen sac containing male pollen) and the filament (the stalk holding the anther).
Stigma: The stigma receives the male pollen.
Style: The style is a hollow tube supporting the stigma and connecting to the ovary.
Ovary: The ovary contains ovules (egg-cells), which after pollination produces the seed(s). A flower carpel, the female reproductive part, consists of a stigma, style and an ovary.

The botanical term of perianth refers to the calyx and the corolla as a unit, especially when they are no petals present on the flower or when the calyx can't be distinguished from the corolla.

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Unisex Flowers

Flower Carpel showing Stigma, Style and Ovary
Flower Stamen showing anther and filament

Compared to a bisexual flower (shown above) unisex flowers either feature only male reproductive organs, which are stamens consisting of filaments and anthers (picture on right) or only female reproductive organs, carpels made up of an ovary, style and stigma (left). Click images for an enlarged view. It is possible for a flower to have more than one style, which can be split and forked. The fruit produced by the female flower shown here is a capsule with 3 valves (segments), each producing a single seed.
The images show flowers of the Brush Wedding Bush (Ricinocarpos speciosus), that is monoecious, flowers of both different sexes are borne on the same plant. Whereas species with either male or female flowers on different plants are referred to as dioecious.

Flowering Times and Periods

Main reasons effecting flowering times of native Australian tree species are average temperatures and to a lesser degree other environmental conditions such as sunlight and rainfall received. On the east coast of Australia average temperatures depend on altitude and proximity to the coastline. For instance the Native Gardenia Atractocarpus benthamianus will flower in July to August at low altitude in warm location, whereas at an altitude of 900 m flowers appear in October to November. Flowering periods can be very short, only lasting for few weeks, or extend to more than 6 month as is the case with our native hibiscus species, making flowers an obvious initial identification feature.

Flower Arrangements, Types of Inflorescence

Flower spike
Flower spike illustration

A Flower Spike:

Flowers are attached without individual stalks (pedicels) to a single central axis (rachis), which is supported by the peduncle at the base.
The image to the right shows the flowering spike of the Maiden's Wattle Acacia maidenii.

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Flower Raceme
Flower Raceme illustration

A Flower Raceme:

Each flower is attached by its own stalk (pedicel) to a single central axis (rachis), which is supported by the peduncle at the base.
The flower raceme of the Grey Possumwood Quintinia verdonii is shown to the right.

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Flower Panicle illustration
Flower Panicles

A Flower Panicle:

Flowers are held on a multi-branching structure, which can be loosely shaped or form more umbrella shaped clusters as shown in the picture of the White Elderberry Sambucus gaudichaudiana to the right.

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Flower Umbel illustration
Flower Umbel

A Flower Umbel:

Individual flower stalks (pedicels) are attached to the same point on top of a common stem (peduncle).
The Lemon Myrtle Backhousia citridora features this type of inflorescence, another good example is the inflorescence of Fire Wheel Tree Stenocarpus sinuatus (see page 5).

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Flower Corymb illustration
Flower Corymb

A Flower Corymb:

A type of inflorescence where flower stalks branch off at different levels but flowers are held at a roughly even height. Species belonging to the genus Alloxylon Waratahs feature this flower arrangement. The Tree Waratah Alloxylon flammeum is shown to the right.

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Simple inflorescence Plum Myrtle Flower

Flowers on Australian shrubs and tree species can appear in terminal positions i.e. at the very end of young branches, in leaf axils along young growth, along older branches and on tree trunks (cauliflorous). Often tree species can feature a combination of positions as listed before. The picture to the right is showing solitary flower (a simple inflorescence) appearing in the leaf axils of the Plum Myrtle Pilidiostigma glabrum.

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