The Wattles

Genus: Acacia
Family: Mimosaceae

This time of year (late winter into early spring) is a great time to have eyes and a nose.  One of the main reasons for this, is because it is the flowering time for many Acacias.  For those poor souls who have not been acquainted with, or have not paid much attention to this group of flowering plants, they often look like this (a bright, bright mass of yellow):

A bright mass of sweet smelling yellow

There are many species of Acacia flowering around Melbourne at the moment, and with only a little effort they are relatively straightforward to identify.  For a successful ID of Acacias you need to know something about their foliage and flowers.  A copy of ‘Native trees and shrubs of south-eastern Australia’ by Leon Costerman is also highly recommended.  This comes in a big comprehensive book covering common trees and shrubs of NSW, Vic and SA, but also a very handy smaller field guide ‘Trees of Victoria and adjoining areas’ (‘Mini Costermans’).

Underneath a bipinnate leaf. Note pinnae and pinnules.

Acacias have two broad types of foliage :

Bipinnate leaves  are ‘feathery’ and divided into pinnae. The pinnae further divided into pinnules.  All acacias have bipinnate leaves to start with.
In some species bipinnate leaves are replaced as the plant grows older by leaf like bodies called phyllodes.  Some species have broad, flat phyllodes whilst others can have spiny, needlelike or very slender phyllodes.

For ID in the field, the type of foliage (bipinnate or phyllode) is a good spotting characteristic.  After this, other foliage characteristics such as the number and placement of phyllode veins or the position and number of glands are significant characters for identification.

Different types of phyllodes

Look closely and you might see the individual flowers that make up this globular inflorescence. You can see the number of closed flower buds on the inflorescence on the right.

Individual flowers of Acacia species are tiny.  These tiny flowers are aggregated together to form an inflorescence and Acacias also have two broad inflorescence types: globular or cylindrical.

This division of inflorescence structure is also an important grouping characteristic for ID in the field.  Most Acacia species flower from late winter to early spring.  Time of flowering can be useful to distinguish between some species.

Single globular inflorescence, cylindrical spike and a raceme of globular flower heads.

An Acacia seed pod, a typical pea pod

Finally the fruiting pods are important features.  Size, shape and surface texture are important.

In mini Costermans (which you should put in your pocket before leaving the house, always) the first major groupings occur between :

– Wattles with bipinnate leaves and globular flower heads (go to page 132)
– Wattles with phyllodes and cylindrical inflorescences (go to page 135)
– Wattles with phyllodes and globular flower heads (go to page 138)

Once you have identified one of these broad groups, you can move to another section of the field guide and start looking in more detail at spotting characters such as placement of glands or veins, distribution and flowering times.  Clear drawings with detailed inserts of relevant features such as leaf glands are super helpful and make Acacia ID relatively straightforward.  So give it a go, it is surprisingly satisfying.

For example:

Acacia oxycedrus, photographed July in The Grampians

Acacia oxycedrus (photo left)

Foliage: Stiff green flat phyllodes 2-4 cm long, slightly curved, tapering to a very sharp point, 3-4 raised veins.
Flowers: (Jul-Oct) Yellow, crowded on axis in cylindrical spikes to 3 cm long.

Acacia longifolia (photo below)

Foliage: Flat  green phyllodes, spreading to erect on stiff branches, 2 (-4) main veins, gland near base.
Flowers: (Jul-Oct) Yellow, in spikes.

Acacia longifolia, photographed August at Seaford

 

 

Acacia verticillata (photo below)

Foliage: Green phyllodes mostly in whorls of about 6, often needle-like (or flattened) with sharp point, 8 – 25 mm x 1-2 (-5) cm long.
Flowers: (Jul – Oct) Bright yellow, in soft ovoid or cylindrical spikes 1 – 2 cm long.

Acacia verticillata, photographed in October near Bendigo

Refs

Costermans, L (1994) ‘Native trees and shrubs of south-eastern Australia’.  5th Ed. New Holland Publishers, Australia.

Costermans, L (2006) ‘Trees of Victoria and adjoining areas’.  6th Ed. Costermans Publishing, Australia.

(‘Mini Costermans’ = buy this).

All photos by Me!  For more Acacia love see http://www.flickr.com/photos/cracoo/sets/72157627391145521/with/7970371684/

A baby Acacia displaying both bipinnate leaves and phyllodes

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