Gardeners, like plants, can easily be grouped into categories. The farmer or survivalist who basically lives on the premise that if it can’t be eaten or used to thatch a roof, there’s little point growing it; the artist or designer who grows for beauty, form and experience; or the botanist or scientist who is often a collector or specialist and who adores pontificating on the details.
Thankfully, there’s room for all sorts in the world of gardening and we each have our roles to play. Plants are much the same, and when deliberating over the various attributes of a plant, you can expect to find that many will straddle more than one group.
All flowering plants can be divided into two main groups: the dicotyledons, which start life with two small round and indistinguishable leaves in the sprout stage; and the monocotyledons, which start with one. Although they are strictly classified by this distinction, it is not a characteristic that makes them easy to define. Instead, it is easiest to recognise monocotyledons by their long strappy leaves that have parallel veins. Think anything from pasture grass, palms, bamboo and grains to lilies, iris, flax and orchids. If the strappy leaves and veins are not a giveaway, count the flower petals, which are always divisible by three.
Although the blooming varieties, such as orchids, iris, canna and lilies, are most often listed in garden books as herbaceous perennials, the grasses, or more correctly graminoids, cause confusion and are worth further defining.
TRUE GRASS – POACEAE
True grass includes 20% of the vegetation covering the planet. This family of plants, if removed from the landscape, could quickly bring our economy to a halt. So much so that New Zealand has a specific seed bank based in Palmerston North, the Margot Forde Forage Germplasm Centre, which was set up to ensure we are future-proofed against disease outbreaks, climatic changes or other events that might affect our pastures.
Although the common greener grasses are easily identified, it’s surprising that bamboos are grasses, too. Rather than growing from a stem, the leaves (also called blades) of grasses will generally start in pairs opposite each other at the base of the stem and continue to grow this way up the jointed stems.
As with most plants, the flowers are always a good means of identification. Grass flowers are made up of spikelets, which are normally plentiful and en masse appear as soft feathery, bushy plumes. They are prolific rather than colourful, which accounts for much of their success.
Sedges have triangular stems and accordingly three leaves at one growth point or joint rather than the characteristic two of grass. This family includes Cyperus papyrus, which, as the name suggests, was used to make papyrus in Ancient Egypt. It also includes our native carexes, which are often erroneously referred to as one of New Zealand’s most popular native grasses. They are, in fact, a sedge. If you are still confused, the New Zealand Plant Protection Society has produced a wonderful handbook, An Illustrated Guide to Common Grasses, Sedges and Rushes of New Zealand.
Rushes are mainly wetland plants. Unlike those of grasses and sedges, the flowers of Juncus look more like the popular idea of a flower, although on a small and not particularly colourful scale. Rushes are inclined to be straighter and more upright than grasses and sedges, although this is not always the case and is, perhaps, dictated by their environment. For example, plants that have to cope with a constant flow of water need to have a different form from those that are exposed to wind. These three distinct groups help us to think about the differences between plants and the key ways in which we can distinguish individual species.
Although small and not always available on a plant, seeds are a great means of identification, especially as many are distinctive. The New Zealand Plant Protection Society has also produced An Illustrated Guide to Weed Seeds of New Zealand. Every seed has been photographed and the plant described. After identifying onehunga weed seeds in this guide, my son now rejoices when he finds a prickle in his foot. “A seed travelling on my foot again!” he proclaims.
Flowers are an essential way to identify a plant and its relationship to others. After all, this is how the flowering plant kingdom has been organised by humans for hundreds of years. This is where the sex happens; as with animals, plant families are defined by genetic lines. Flowers are not a foolproof method of identification, however, and with the advent of DNA testing there has been some realignment of species. When observing a flower, look at the colour and form as well as the arrangement of its components: stamen, stigma, filaments, sepal, pistil, style, ovule and petals. This may seem an overwhelming list, but once begun, the dissection of a flower can be mesmerising.
When examining leaves, don’t just look at the shape and colour. Consider also how a leaf joins the stem in relation to another leaf. Are they opposite or alternating or do they encircle the stem? Consider whether the leaf is soft and fluffy or waxy and also think about its size.
A fruit is just one of the many ways a plant distributes its seeds, allowing the offspring of a plant to move away from the parent. This is important for long-lived plants such as trees and shrubs. In a forest, the most likely impact of a tree seedling germinating on the forest floor is proximity to the parent plant. It is thought parent plants release inhibitors to encourage offspring to seed outside the reach of their canopy. Fruit have evolved to be attractive so that something will take on the job of shifting the seed. Their appearance makes them easy to identify, which helps when it comes to distinguishing one plant from another.
Observing seasonal changes in a plant is guaranteed to give a clue to its identity. Consider whether it is deciduous (loses its leaves in autumn) or evergreen. Deciduous trees give you an opportunity to examine the shape of a plant in a new way and to take extra notice of key characteristics, such as the bark. The timing of flowers can provide a clue to determining the difference between closely related plants that look similar but may flower and/or fruit at different times.
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