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

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Using Flowers Characteristics in the Identification of Australian Tree Species

Introduction: Flowers are essential in the classification of native Australian trees and shrubs, but are normally not the primary method (with exceptions), when identifying native species in their natural environment. Reasons for this are; the often short term life span of flowers, being out of reach for closer inspection (i.e. flowers are held in the higher canopy) and often being rather inconspicuous. Although species may not flower every year or only commence flowering 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 January 2019.
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Flower Anatomy, Parts of a Flower

Flower Anatomy
Hairy Lollybush Clerodendrum tomentosum
Flower Calyx

Sepals: Appendages forming the base of a flower, which can be totally separated or fused together with free standing protrusions (lobes) at the apex. The shape of sepals can vary from leaf-like structures 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 base of the flower. 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 (shown left) retains the calyx at the base of the fruit, whereas species of the genus Syzygium, commonly known as Lilly Pillies and Satinashes (shown right), at the top end of the fruit.

Pedicel: An individual flower stalk in a compound flower arrangement (Inflorescence).
Peduncle: The primary flower stalk supporting the rachis to which individual stalks (pedicels) are attached to, or the stalk of a solitary (simple) 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, but might attract pollinators like insects by means of shape and scent.
Stamen: Stamens are the male reproductive parts of a flower. A stamen is made up of the anther (swollen sac producing male pollen) and the filament (the stalk supporting 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 one or multiple 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. A unit of fused carpels is known as a pistil.

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. The image of the female flower shows a pistil consisting of 3 fused carpels, each with its own split style, stigmas and ovary. The fruit produced by the female flower 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, meaning that flowers of both different sexes are borne on the same plant. Whereas species that produce either male or female flowers on different plants are referred to as being dioecious.

Flowering Times and Periods

Pink Hibiscus Hibiscus splendens Flower

Main reasons effecting flowering times of native Australian tree species are average temperatures and other environmental conditions, such as amount of sunlight and rainfall received. On the east coast of Australia average temperatures depend on latitude, 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 900m 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 their distinctive flowers an obvious and practical identification feature in the field. (The native Pink Hibiscus Hibiscus splendens is shown to the right).

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:

Individual flowers are held on a multi-branching structure, supported by a common stalk (peduncle). Panicles 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 stalk (peduncle).
The Lemon Myrtle Backhousia citriodora 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 individual flower stalks branch off the rachis 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 of 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 leafless branches (ramiflorous) and on tree trunks (cauliflorous). Many tree and shrub species can feature a combination of locations in which flowers appear. The picture to the right is showing a solitary flower (a simple inflorescence) appearing in the leaf axils of the Plum Myrtle Pilidiostigma glabrum.

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