I was convinced these were J australis: 1 m tall, culms to 3.5 mm wide, cataphylls loose to 15cm long. But then I sectioned culm to see the pith and found no cavities (my pic 2). Instead the pith is a fine sponge - my pic 3 shows a thin slice cut out of the pith showing the pores of the 'sponge' that are 0.05 to 0.1 mm diameter