Janet Hodgkiss
Species names need not be confusing, and once you become familiar with the botanical Latin and Greek terms, you’ll often notice that they are quite descriptive. Two acacia species, Acacia aphylla and Acacia trigonophylla, at a quick glance look very similar, but their species names tell us a lot about the plant itself, so let’s have a closer look.
Credit: Janet Hodgkiss)
Both of these species names refer to a plant part – the leaf. Before we look at how these words are modified to be more descriptive, let’s get to grips with some basics.
The part-word ‘phyll’ is derived from the Greek word for leaf and is used in plant names to describe or refer to leaves or leaf-like structures. It is handy to know this as it can help tremendously with plant identification.
This part-word -phyll (pronounced ‘fill’) can have other endings such as -phylla or -phyllum (these are pronounced ‘filla’ or ‘fillim’). The pronunciation is important to distinguish it from another very similar word in the realm of biology, the word ‘phylum’ which is pronounced like ‘file-um’.
The term phylum, and its plural phyla (pronounced ‘file-uh’), is a major taxonomic rank or group in biology, sitting below kingdom and above class.
In botany, the term or rank of division has been traditionally used instead of phylum but the International Code of Nomenclature for algae, fungi and plants accepts division and phylum to be equivalent.
So, while similar in sound and looks, it’s important to get your pronunciation of -phyllum and phylum correct, especially when you’re talking to other people and using plant names, as the species names are then more likely to make sense and stick in people’s minds when they know it relates to the leaf.
Now that you know -phyll refers or relates to leaf, you’ll likely see it popping up in different words. For example, heterophyllous describes a plant with different types, shapes or sizes of leaves; chlorophyll, the green pigment found in plants is primarily found in leaves; a cladophyll is a flattened stem that looks and functions as a leaf; and a phyllode (meaning leaf-like) is a modified petiole (leaf stem) that functions like a true leaf.
Phyllodes are commonly seen in our Australian acacias, and true juvenile leaves or partially formed phyllodes bearing reduced leaves are usually seen on younger plants or seedlings.
Some acacia species do carry true leaves as mature plants and you’ll know these as being the species with the feathery, compound leaves seen in Acacia dealbata (Silver Wattle), Acacia mearnsii (Black Wattle) and Acacia baileyana (Cootamundra Wattle).
However, the ‘leaves’ we see more often on acacias are phyllodes. Phyllodes are an evolutionary survival strategy that allows plants to adapt to drought conditions and poorer soils so they thrive in arid and semi-arid parts where other plants may not survive. The leaf blade is lost and is reduced to the leaf stalk, and in some cases may be completely absent. In some species the leaf is modified into a thorn, or a thorn may sprout from a node where a leaf stalk would otherwise develop.
This brings us back to the two similar acacias mentioned earlier and what their species names mean or allude to.The species names of Acacia aphylla simply means without leaves or phyllodes. Its common name Leafless Rock Wattle is very appropriate as it clearly has no visible leaves or leaf-like structures on the plant. The shrub is simply a tangle of curved, tubular, rigid branchlets that are sharp or pointed at the end.
Credit: Janet Hodgkiss
Acacia aphylla is endemic to the area east of Perth in Western Australia and its conservation status is listed as threatened. In its natural habitat it is found growing in eucalypt woodlands in sandy, gravelly and clay soils.
Credit: Janet Hodgkiss
It grows 1–3 m tall with a spread of up to 2 m, in full or part sun, and bright yellow, globular flowerheads are produced singularly along the branchlets in late winter to spring.
Acacia trigonophylla has no visible leaves or leaf-like structures. Phyllodes in this species are continuous with the branchlets and form narrow triangular wings 1–2 mm wide. The edges of the branchlets are slightly rough to the touch.The -tri part of the species name trigonophylla refers to the three-sided appearance the phyllodes give to the branchlets. When the stem is cut, this triangular feature is very obvious.
Credit: Janet Hodgkiss
Credit: Chris Larkin
Acacia trigonophylla is endemic to Western Australia where it has a widespread and scattered distribution. It is found growing in sandy granitic or lateritic soils, in swamps, on hillsides and amongst rocky outcrops.
The lack of true leaves gives this upright, multi-branched shrub a lovely airy appearance. It grows 1–2.5 m tall and globular, yellow flowerheads appear from August to November.
This is the first in a series where we’ll take an in-depth look at leaves.
