Scientists Dr Maurizio Rossetto and Dr Robert Kooyman next to a fallen tree in The Big Scrub, from a recent trip to Nightcap National Park to make the video below. The video production consisted of a crew of one – me! A beautiful place and hopefully an interesting story.
What is the video about?
The National Herbarium NSW of the Royal Botanic Gardens in Sydney has been doing interesting scientific research into rainforest tree distribution and rarity in Northern NSW. They have found links between rarity and the relatively recent local extinctions of large fauna such as the Cassowary. This video features scientists Dr Maurizio Rossetto and Dr Robert Kooyman. As well, it features the recently discovered and extremely rare tree Eidothea hardeniana as well as trees from the Gondwanan family Elaeocarpaceae.
I like it when I understand enough about a plant family to recognise a plant as belonging to it.
Lamiaceae is one family that I get. There are a few reasons.
Lamiaceae is also known as the ‘Mint-family’. Mint (Mentha) is a member and like mint most of Lamiaceae’s species have aromatic leaves. And what aromas! Rosemary (Rosmarinus), Thyme (Thymus), Sage (Salvia), Basil (Ocimum) and Oregano (Origanum) are all Lamiaceae plants.
Lavender (Lavandula) you ask? Yes, most definitely Lamiaceae.
But, there are more than 7000 Lamiaceae species worldwide, making it the 7th largest plant family.
One of Lamiaceae’s 44 Australian genera is the native genus Prostanthera or Mint-Bush which has an unbelievably wonderful aroma. It is a fantastic plant for gardens. Enjoy the smell as you rub up against it or crush some leaves. Prostanthera occurs widely from alpine to arid areas.
A well known native is Westringia fruticosa which is often used in landscaping, but is naturally found hanging on rocks exposed to the sea in the harshest conditions. Its common name is Coastal Rosemary but unlike Rosemary and most other Lamiaceae species, Westringia fruticosa has no aroma.
The family is quite recognisable. The plant below is growing in coastal heath in Yuraygir National Park on the NSW north coast. It looked to me like Lamiaceae, but I didn’t know the genus or species. I asked Trevor Wilson from the Botanic Gardens in Sydney who is studying the genus Prostanthera and he identified it as Chloanthes parviflora. Chloanthes is a genus of Lamiaceae.
Or in the arid zone another species from a different genus Teucrium occurs – but again the flowers look like Lamiaceae.
Lamiaceae flowers are quite distinctive. They are zygomorphic (bilaterally symmetrical) and they are labiate. Labiate means that one or more petals can form a lip (Clarke and Lee, 2002). They have 2 or 4 stamen.
Lamiaceae stems are usually square shaped. If you run your fingers along a stem of Rosemary or Westringia for example you can feel the ridges.
The leaves are usually opposite.
So when I see labiate flowers, I grab some leaves and take in the aroma. I rub the stems – feeling the square shape and think Lamiaceae!
Another significant plant family in Australia and around Sydney is Rutaceae.
So, It is one to learn. It’s fairly easily recognised, it usually features plants that have oil glands on the leaves, when they are crushed they provide an aroma. You can see the oil glands in many of the photos on this page.
Rutaceae also has beautifully arranged flowers.
It is economically important because it includes Citrus and landscaping plants like Murraya. It is also conidered important in our understanding of Gondwana but I’ll come back to that.
Flowers are key to understanding and recognising plants. They are incredible organs, highly variable between families but often within families they are pretty consistent. If you can learn to recognise one flower in a family, you can recognise others.
Rutaceae’s flowers are what is considered ‘perfect’. They contain functioning male (stamens) and female (carpels) parts. As well, in Rutaceae they are arranged in a whorl. A whorl means each part is stepped so that it doesn’t overlap the part beneath it.
The flower parts from outside to inside are
Sepals – the leaf like protective bits that cover the growing bud.
Petals – the colourful bits sit above the sepals. In Rutaceae there are just about always 4 or 5 petals. These are radially symmetrical which is known as actinomorphic.
Stamens – the male part. In Rutaceae there are either the same amount as petals or double. So if I see 4, 8, 5 or 10 stamens in flowers that are perfectly symmetrical I start thinking thinking Rutaceae. Of course, there are exceptions.
Carpels – the female part which contains the stigma which is adapted to accept only compatible pollen and is joined to the ovary by the style. The Correa alba photo above is the best for highlighting the carpel.
Once you recognise the family then you can think about relationships between genera. How, for example, are Crowea, Boronia and Phebalium related to other Gondwanan genera like the South African genus Diosma (pictured below) or Calodendrum. Calodendrum a genus which means beautiful tree contains the gorgeous Cape Chestnut.
The Melbourne Botanic Gardens are using Rainforest and Sclerophyllous Rutaceae species in Australia and New Caledonia (also Gondwanan) to uncover relationships and clues to geological histories.
And of course, it can keep you thinking about the Citrus family which is thought to have its origins in China and has been cultivated for the past 4500 years.