Monthly Archives: October 2011

Broadleaf Grass-tree

Xanthorrhoea arborea

“A grass tree to 4m tall, with an aerial trunk” – NPOS p.278

Another unique and distinctive plant of the Australian bush. Grass trees have a short stout trunk that is often burned black from previous bush fires terminating with a dense tuft of long grass like leaves radiating from the crown. They are very slow growing at a rate of only 1cm per year, that makes a little 30cm tall plant almost as old as me! They make up for it in life span living up to 600 years old. Every year grass trees sprout a large ( up to 2m ) woody spike from the center of their leafy crown. The top section of the spike is densely covered in small nectar rich flowers.

They were a very useful plant to Aboriginies, the nectar from the flowers can be licked off, or the entire flower head soaked in water to make a sweet drink, enjoyed fresh or slightly fermented. The flower spikes were uses as spear shafts and resin could be collected from the trunks and the leaf basses and processed to be used for tools and weapons.

I’ve always wanted a grass tree in the garden, I recently bought one from a local nursery. It’s a Xanthorrhoea johnsonii which I’ve now learned is more of a Northern NSW and Queensland species, I hope it does ok here. But not too well, don’t want it colonizing the bush and competing with the native ones!

Broadleaf Grass Tree
Broadleaf Grass Tree growing in the bush behind the house. The trunk is hidden by the leaves but it's probably 60cm tall, making this plant about 60 years old.
Grass tree leaves
Close up of the leaves of the grass tree. The grey colouring on the underside is a powdery resiny coating that can be wiped off.
Grass Tree Leaves
The dense leafy crown of the grass tree

more info:

Bird’s Nest Fern

Asplenium australasicum

“A spectacular epiphytic fern with long, tough, radiating leaves” NPOS p.306

Great! I’ve found another uncommon fern. It’s hardly fair with the Bird’s nest fern though, it stands out from most other plants in the bush with it’s bright yellow-green fronds and it’s distictive rosette habit.

This one was growing on the edge of a sandstone cliff in the bush out the back.

Bird's Nest Fern
Bird's Nest Fern growing on sandstone. Found this when I was out the back checking on the sewer leak.
Bird's Nest Fern Sori
Underside of a frond showing rows of sori

more info:

Coral Fern ( G. microphylla )

Gleichenia microphylla

“Habit and Habitat as per G. dicarpa. Uncommon”NPOS p.314

Yet another Coral Fern! Along with the Pouched Coral Fern ( Gleichenia dicarpa ) and Gleichenia rupestris the G. microphylla compleats the entire set of coral Ferns found in Sydney, acording to NPOS anyway.

G. microphylla has features of both G. rupestris and G. dicarpa. It had very fine small fronds that are a deep green colour and convex on the top like G. dicarpa. But on the undersidethey are flat or just slightly concave like G. rupestris.

I fond this specimen growing on the side of a damp sandstone cliff at the back of the house. There was some G. dicarpa growing there too. G. microphylla is meant to be uncommon in the area so I’m happy to have found it so close by.

Gleichenia microphylla
G. microphylla Coral Fern growing on a damp sandstone cliff. I came across this when I was out the back looking after the blocked sewer main. Thanks sewer!
Gleichenia microphylla
G. microphylla frond. It looks a lot like the Pouched Coral Fern from the top. but under the leaves it was flat, no pouches.
Gleichenia microphylla
Close up of the fronds.

more info:

Basalt Columns at the Mt Tomar Botanic Gardens

One of the reasons Mt Tomar supports such lush vegitation is that it’s soil derives from the basalt which caps the mountain. Basalt is a very fine grained, dark coloured rock of volcanic origin. It’s abundant in iron, magnesium, calcium and other elements and weathers to form a mineral rich soil that plants love.

I was hoping to see some of the basalt flows but the weather was pretty miserable so we didn’t spend as much time as I would have liked looking about. I did notice the garden walls just below the visitors center were made from presumably local basalt columns. A closer look at the rocks revealed olivene phenocrysts and small vesicles some of which were lined with white crystals, possibly calcite or aragonite?

The walls looked good, and it’s pretty amazing to think that a few million years ago they were part of a massive lava flow!

Columnar Basalt
Columnar Basalt retaining wall at the Mt Tomar Botanic Garden. See Will for scale.