Thursday, 9 August 2007

#25 What on Earth are Earthstars?

No, they are not strange exotic blooms, and nor are they pretty little man-made trinkets. They are fungi which pop up in gardens, on the forest floor, and even in sandy heaths.

Delicate and pretty with a shimmering spherical 'ball' surrounded by a petal-like 'skirt', I photographed this earthstar in Barrington Tops National Park - April 2006

Geastrum, commonly known as Earthstars, are characteristically similar to Puffballs, but with the noticable difference of an added outer layer.

What are fungi, anyhow?

The vast and varying array of fungi sprouting in forests, fields and gardens are the temporary reproductive organ (or fruit body) sent forth by its underground parent when climatic conditions are favourable.

Fungi do not belong to the plant kingdom as they do not depend on light as an energy source, therefore, do not photosynthesise.

The major part of a fungus is essentially invisible, consisting of microscopic threads (called hyphae), weaving their way through the substrate. The substrate could be soil, wood (living or dead), or other dead or living material. A mass of hyphae is called a mycelium. Occasionally these threads can be seen near the soil surface if a 'mushroom' is disturbed.

Almost 'flying saucer-like' in appearance, this spore-filled earthstar sac sits atop its recurved outer skin - in the rainforest of Barrington Tops National Park - April 2006

The main function of the fungus fruiting body in the many forms that we observe, is to produce spores for reproduction. These dust-like spores are held on the gills, spines or pores of the fertile surface of fungi, or in the 'sac' of puffballs and earthstars.

Depending on the structure of the fungus, spores are dispersed by air currents, rain drops or running water, or pressure produced by vegetation movement and passing animals. Some spores are ingested by animals and dispersed as they are passed through the gut. Amazingly, some fungi even project spore-filled 'packages' in a cannon-like fashion. And thus, new fungi colonies are established.

Earthstars start out as 'eggs' with a double layer of 'skin' (right). The outer layer splits to reveal the inner 'sac' (left)

It is the responsibility of the mycelium (underground threads) to provide nutrition. This is a complex process, but put simply, there are three main categories relating to feeding:

Saprotrophic fungi break down components of dead organic material. These provide a vital role in recycling the Earth's accumulation of dead vegetation and animals, returning nutrients to the soil.

Parasitic fungi obtain nutrients from living orgainisms with no benefit to the host. This not only includes living trees and other plants, but also other fungi and animals such as underground larvae of moths.

Symbiotic fungi form an association with a living organism which is of benefit to both. Fungi whose hyphae form a relationship with roots of trees and other plants are referred to as mycorrhizal.

Notice the spore-containing sac of the aging earthstar on the left is beginning to disfigure due to pressure exerted on the paper-thin skin by wind and rain. On the right is a newly-emerged earthstar that has not split its outer layer.

I have found earthstars in a wide variety of habitats ranging from moist mountain rainforest, dry woodland, grassy fields and gardens, to the nutrient-poor sand plains of south west Western Australia. All the Geastrum specimens here were photographed in the Hunter Valley.

The structure of Earthstars

The fruit body initially resembles a puffball as a spherical object sitting on the ground, usually in small loose groups or solitary. It can have a sandpaperish appearance or be coated in powdery flecks. The outer layer of the fungus will split at the top and peel downwards to form a petal-like 'skirt', giving rise to the "star" shape it is named for. In some species, the outer layer will arch to push the spore sac higher.

As the outer skin peels back, the mouth (or stoma) of the inner spore-bearing recepticle is exposed. At first, the spore mass (gleba) is firm, but quickly matures to a powder which is dispersed through the opening as rain drops or wind apply pressure to the paper thin walls.

A Geastrum species that arches to push the spore sac up - in a park garden at Wollombi in the Hunter Valley

As yet, I have not attempted to identify any of my Geastrum finds, but according to Fungimap (a project run by the Royal Botanic Gardens Melbourne), there are only about 10 species in Australia, so it might be possible for me to narrow down likely identifications, with considerable persistence.

For those interested in a more detailed account of the structure of Geastrum species, this Fungimap page provides a good description.

A mature Earthstar and 'egg' - Barrington Tops NP

You're likely to encounter Earthstars at any time of year, but predominately in autumn and early winter, and often following rain. I found several Geastrum in mulched public gardens as the ground started to dry out after the June 2007 Hunter Valley floods. Delightful little things, arn't they?


Esperance Blog said...

Very interesting and educational Gaye, I have a species around me growing in sandy soil, usually near the upper margins of ephemeral swamps. Mine are quite small varying in size from a five cent to a fifty cent piece. Have you seen any larger ones?

yewenyi said...

Thanks for the explanation, we found some in the Blue Moutains, and until I read this I thought they were puff balls.

my photo

Gaye from the Hunter said...

hello Jack,

most that I have seen locally have been between about 3.5mm and 4mm, perhaps some recent finds have been a little bigger still. It's quite interesting that some mature earthstars don't appear to be attached to the ground.


Gaye from the Hunter said...

hi yewenyi,

I'm pleased that you have found my blog. If you are particularly interested in fungi, I have a fungi blog that you will find following the link to my profile.

Your Blue Mountains picture of the earthstar is lovely - a nice specimen.


Denis Wilson said...

Hi Gaye

Nice photos. In my former garden, in Canberra we had hundreds of these earth stars, in deep leaf litter under Cedar trees (Cedrus atlantica). My favourite "stomach Fungus" is the Lattice Fungus, the first time I accidentally sliced the top off one, while weeding, the inner "ball-like structure" popped out and the "ball" rolled across the ground towards me - I thought it was some kind of animal. Scary - for the uninitiated.

You have excellent photos. I have never seen the uplifted, pointy type in photo 2. The last photo is also excellent. Good explanations.


Gaye from the Hunter said...

hello Denis,

I am thinking that the "lattice fungus" that you mention might be Astraeus hygrometricus that now has the common name of Barometer Earthstar. The pointed 'skirt' has a tessellated surface. But perhaps I am thinking of the wrong one completely.

There are different families amongst the Earthstars, so I am presuming there are distinct characteristics that separate them, but as yet I have no idea as to what they are. One day I may investigate this further, but it's too technical for me to get my head around at the moment.

They are indeed odd looking things, especially for the uninitiated, as you say. Unfortunately, I have never seen one in my garden.

Thank you for your comments Denis.


Roger B. said...

Hi Gaye,

Thanks for leaving a comment on my blog.

I really enjoyed reading your post about earthstars. I've seen a few here in the UK, but I've never had an opportunity to photograph them.

By the way, one or two species of fungi from Australia and New Zealand have turned up in the UK recently. They probably hitched a ride with tree ferns and other imported plants.


Roger B.

Gaye from the Hunter said...

hi Roger,

I was pleased to find your blog. It is always interesting to take note of observations and experiences of others who are genuinely interested in and concerned for the environment in which they live. Although the nature you share is half a world away from my backyard, it is part of the *big picture*, and therefore is of interest to me.

I had no idea that Australia exported tree ferns. I am hoping these would be propagated plants, and not plants that have been harvested from the wild. Do you know any more about this?


David Young said...

Nice photos of the Earthstars Gaye.
The one on the top of the post is very well captured, showing a very high degree of textural definition and the colours are so soft.
Your site is a pleasure as always.

Gaye from the Hunter said...

hi David,

thank you.

That is my favourite too. It was dark in the rainforest and I used an exposure of 2.5 seconds with f20 and ISO 100 (even though lighting is bad, I use ISO 100 - it's just a habit I am reluctant to break from my days of transparency film). The long exposure helps to create the soft colours, sometimes too much so, but it suited this one. It really was a beautiful specimen.


Roger B. said...

There's some info about tree fern imports on a UK government website:

Gaye from the Hunter said...

Roger, I've read the link you provided, along with connected links, and it appears that exported tree ferns are propagated plants. This is good. And there is some interesting reading there as well.

Thank you for seeking that site for me - much appreciated.


Anonymous said...

i think ur your pics are pretty fasinating i think the contrast is great i enjoy looking at fungus it brings out my true insides thank you for the wounderfull information it helped me understand stuff

john curry

Gaye from the Hunter said...

hello John,

it's great to know that others are enjoying fungi out in the field or in the backyard. I'm glad that my pictures and information were of some use.

Thank you for leaving a comment.