Field of Science

Botanical questions - grass trees

grass trees living tissues inside them, what is this purpose?? and how are they adapted to fire??

Here’s a recent question (10/27 via comments) submitted to the Phactor, and this is my best effort to answer what seems to be asked. Grass trees are the common name for some yucca-like plants in the genus Xanthorrhoea native to Australia. They grow slowly and can live for 200-500 years. They start out looking like a grassy/yucca-like tuft of stiff-leaves and with time they develop a trunk largely composed of compacted leaf bases, which is very resistant to fire, so they do not burn, although they develop a good black scorching, but insulate the living tissues within from the heat of brush fires. Their habitat is generally open savanna like forests or chapparel, areas subject to occasional or even seasonal burning. The trunk is hollow and the living portions within are adventitious roots that connect the live top to ground (nice picture here). Dead leaves can form a considerable mantle around the stem if the plant has not been subjected to fire. While the outer leaves of the crown get burned the dense whorl protects the growing apex within. They are a great looking plant, and so subject to landscape exploitation much like cacti in the SW USA. My CSIRO colleagues said they did not transplant easily or well. They produce a really distinctive terminal flowering stalk and tough fire-resistant fruits. Fire seems to stimulate seed dispersal and germination.

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