Yup Mulefat is somewhat hollow and very light in weight as compared to "arrow weed". Mulefat also tends to grow in Riparian areas and need alotta moisture. A good tip is smell the shaft or plant, it stinks like Horse piss. Funny because the bush in my Apache language is called just that "plant that smells of horse piss". Arrow weed is super dense (arid plant) likes to grow in sandy soils. I'll find them in huge stands. Bark is white/light grey and smooth.