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Why live on a cliff?

Livistona lorophylla on large cliff face

Unable to enjoy the view, it is worth asking why some plants prefer living on cliffs.

While not many plants occupy cliff faces (and some that do just grow everywhere), a select group of cremnophiles (cliff-dwellers) specialise in this unusual habitat.

While usually a harsh environment, often subject to intense heat, wind and water-stress; once a plant has adapted to this environment, it can be remarkably stable.

The small amount of water captured by a cliff face changes little under fluctuating rainfall patterns. Often, water is actually sourced from rainfall that filters through from plateau tops above the cliff, a quantity that is also relatively stable, given that most water flows away as surface run-off.

Another important factor is the sparse vegetation on cliff faces means fire is excluded, or at least a rare event, so scarce resources don’t need to be allocated to regenerating after a fire.

Cremnophiles are known from many different plant families. While only a small proportion of the Kimberley flora, a number of species appear to be restricted to cliff faces (see Barrett & Barrett 2011; Barrett & Henwood 2015).

Some plants, such as the unusual herb Lindernia cleistandra (Linderniaceae) pictured below, are highly specialised to their cliff-face environment. This herb grows under rock overhangs, often hanging off the roof of shallow caves. The flowers are presented prominently, but this would normally mean the seeds fall to the ground, and away from suitable habitat. This species has solved that problem by curving its fruiting peduncles back towards the rock, where they are pressed against the face as the seeds mature. Presumably water and/or ants then have a better chance of dispersing the seeds to a new rock crevice.

Other unusual species found on cliff faces in the Kimberley include Mackenzie's Wattle (Acacia mackenziei; top left), the Kimberley Cliff Boronia (Boronia cremnophila; top right), Keep River Kunzea (Kunzea sp. Keep River; bottom left) and Cliff Spinifex (Triodia cremnophila; bottom left and bottom right).

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