In the latest Fern Gazette Masohiro Kato has written a fascinating review article on rheophytic ferns. Rheophytes are plants that have evolved adaptions to living in fast flowing streams and rivers. The flows are often intermittent and torrential and it is a challenging habitat for plants to thrive.
Earlier this year I was in Sarawak, Malaysia, staying adjacent to Mount Santubong, a relatively small National Park located on the coast. On one of my walks in the rather dry forest I came across a colony of the rheophytic fern Dipteris lobbiana growing in a rocky stream bed. This is a fern I had always wanted to see but never really expected to find. It is found in Borneo, Sumatra and the Malaysian peninsula.
It is a beautiful fern but the fronds are not typically fern-like. Each frond is divided into two halves and these are then dichotomously divided into narrow lobes that spread out from from a roughly central point giving a circular outline. The structure is similar to other species of Dipteris however the narrow lobes are an adaption to the rheophytic life-form. The narrow lobes allow the fronds to flex and survive the battering of the torrent. Much more information is provided in Kato’s article.
I am intrigued how this fern gets established on the rocks. There were abundant gametophytes present that must get rooted onto the bare rock between times of spate and are then able to survive flash floods to go on and eventually produce mature sporophytes.
There were few fertile fronds and most were dead. I presume they are seasonal and produced during the dry season that allows the spores to be shed and dispersed when water levels are low for longer periods thus enabling them to germinate and establish before the wet season.
Dipteris lobbiana growing on a rock in mid-stream. Note the smaller plants colonising rocks on the far bank.
More plants growing half-submerged
Frond showing two opposite halves with bifurcating lobes.
Typical mature frond showing circular outline.
Young sporophytes growing from a mass of gametophytes
More juvenile sporophytes colonising a bare rock in the stream.