Thursday, July 19, 2012

The Early Orchids are Out

Blunt Greenhood
Pterostylis curta

These little chaps are just beginning to flower in the Goomburra National Park.

There are several different local species of greenhood. This one can be identified by the rather short “horns”, (actually the tips of two of its sepals).  “Curta” means short. However, the best identifying characteristic is the labellum, which has a sideways twist.

The labellum is a little petal, different from the other green ones, which pokes out of the flower’s “mouth”  like a tongue.

You may notice, as you examine a flower closely, that the labellum suddenly flicks back inside.

What it’s doing is showing you its quick reflexes. If there had been a potential pollinator  on that labellum, the orchid would have flicked its little visitor back against its style. After holding it prisoner for 30-90 minutes,  the labellum would have relaxed as it began to reset. The little gnat would then struggle up towards the light coming in the orchid’s translucent hood. As it did this, using the tiny hairs on the labellum as footholds, a little bundle of pollen would have stick to its back, ready to pollinate the next greenhood that it found itself struggling out of!
The insect pollinators are thought to be all males, and may be attracted into the flower by a “perfume” resembling female gnats’ pheremones.
The labellum usually takes 2-3 hours to reset, but is faster on warm days, and can take all day if it’s cold.
Greenhoods are deciduous orchids. This means that for more than half the year they consist of nothing but an underground tuber. In winter they use up the food stored there, to grow a little rosette of leaves. In a poor year this might be all they can manage, and there is no flower. Food manufactured in the leaf (by photosynthesis) is then used to grow a new tuber to help the plant survive the next year. In a good year (with plenty of sunlight and water for photosynthesis), colony-forming greenhood species like this one also grow several new tubers, each one becoming a new plant.

Just at present, the colonies are showing some flowers and plenty of buds, so it’s a good time to look for them. Their favourite situation is on well-drained slopes and cuttings, with a south-easterly aspect.

Thursday, July 12, 2012

Scrub Sandalwood

Santalum obtusifolium
This little-appreciated bush tucker plant grows in the Ravensbourne area, on red soil. Its summer fruits are delicious. Just 1cm diameter, they are dark red, and juicy, with a single seed in the middle.
I had a good crop on my little plant this year. I am kicking myself that I didn’t photograph them. There’s a picture on Wikipedia, if you’re curious.

This sandalwood is a shrub, usually growing to about 1m high. It can grow in full sun, but also likes a situation with dappled shade.
It likes its soil well-drained, and it’s a good idea not to let it get too dry in its first season.

Here’s a young specimen at Peacehaven Botanic Park.
Note the grass growing at the base. Like all sandalwoods, this species is a partially parasitic plant. It is able to draw nutrients from the roots of plants around it, usually native grasses. It’s a good idea to plant some suitable grass with each sandalwood seedling.

Thursday, July 5, 2012

Frosty Bursaria

Bursaria incana
The delightful thing about living in this climate is that winter has hardly time to get started before we see our first signs of spring.
The early orchids are out already, and the wonga vines are flowering gloriously .

This lovely bursaria, growing wild near the Bunya Mountains,  had a glowing halo of flowers last week.

 Native bees are said to love these flowers, but it was so cold when we came across this plant that few insects had ventured out.


Here’s a specimen growing at Peacehaven Botanic Park. At five years old it’s already a handsome small tree, with a dense green canopy.

“Incana” is latin for frost, and the name is a reference to the white-backed leaves of this plant. They  distinguish it from its later-flowering cousin, the sweet bursaria, Bursara spinosa (See article April 2009) . Despite its name, it might be killed by frosts in its early years, though it tolerates them once it has gained a bit of height.
Some people call this tree “prickly pine” which seems a bit unfair. The suggestion of prickliness puts some people off growing it, yet the plant outgrows its juvenile prickly stage in just a few years.
This is a very desirable garden plant, attracting birds and butterflies. It can be left to grow into its natural shape, making a good windbreak, but is also amenable to pruning so can be trimmed up for a small shade tree, or kept low, as a hedge.