The species of Geastrum are known colloquially as earthstars. Each mature fruitbody consists of a puffball-like spore sac atop a star-like base. Some species are easy to identify visually, others are not. Before you started looking at microscopic details, some of the questions you'd ask when trying to identify a Geastrum are:
Does the spore sac sit directly on the base or is it held up by a stem (and if so, what is its size)?
Are the arms of the base hygroscopic (in other words, do they fold inwards in dry conditions and open out in moist conditions)?
Does soil/debris adhere tightly to the undersides of the basal arms or are they free of soil/debris (or at least where any soil/debris is easily removed by light brushing)?
What is the nature of the apical mouth, through which the spores puff out? Two examples are a (1) conical, strongly pleated mouth (as shown here, http://www.cpbr.gov.au/fungi/images-captions/geastrum-sp-ostiole-0144.html) and (2) a fibrillose mouth (http://www.cpbr.gov.au/fungi/images-captions/geastrum-sp-ostiole-0143.html).
You'd also note colour, texture and size.
Geastrum sp. is listed in the following regions:
Canberra & Southern Tablelands | Southern Highlands | South Coast | Hume | Loddon Mallee
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MapsANBG Black Mountain Bruce Ridge Bullen Range Cooma North Ridge Reserve Fadden Hills Pond Federal Golf Course Ginninderry Conservation Corridor Hughes Garran Woodland Hughes Grassy Woodland Isaacs Ridge Isaacs Ridge and Nearby Lake Ginninderra Lower Cotter Catchment Mcleods Creek Res (Gundaroo) Molonglo Gorge Molonglo River Reserve Mount Ainslie Mount Majura Mulligans Flat Namadgi National Park Pine Island to Point Hut Queanbeyan-Palerang Regional Council Red Hill Nature Reserve Red Hill to Yarralumla Creek The Pinnacle Tidbinbilla Nature Reserve Uriarra Recreation Reserve
Points of interestPoint 5438 Pollinator-friendly garden Conder1
PlacesActon, ACT Aranda, ACT Belconnen, ACT Boro, NSW Bruce, ACT Bungendore, NSW Bywong, NSW Carrick, NSW Conder, ACT Cooma, NSW Coree, ACT Cotter River, ACT Crooked Corner, NSW Deakin, ACT Downer, ACT Dunlop, ACT Fadden, ACT Florey, ACT Forde, ACT Garran, ACT Googong, NSW Greenway, ACT Gundaroo, NSW Hackett, ACT Hall, ACT Hawker, ACT Hereford Hall, NSW Higgins, ACT Hughes, ACT Isaacs, ACT Karabar, NSW Kowen, ACT Majura, ACT Molonglo Valley, ACT Ngunnawal, ACT O'Connor, ACT Paddys River, ACT Parkes, ACT Queanbeyan East, NSW Scullin, ACT Stromlo, ACT Tennent, ACT Urila, NSW Wanniassa, ACT